nwHiiTj ifiliuuijifiiii i i i j ( 1 1 1 1 1 1 1 1 1 < i ( i ) .Jinn.,,.. . llliHliill II 111 U«!l!!Ht{|| hi ill! | ll . . ti H(i|(ih(|iih:iii iHiiiiiiiiiiimi'i'i'iriiiiiiiiiiiiii 11 1 i 1 i I II I ll I ll l i ' I i ; ■ : ' ; •' i ' ' I ■ i i H 1 1 1 1 1 MJUBgnWffr ■BBHMhBHHU niu iiuSiiiiifiliitml iiliuii mi iiiiiiiiiiiiiiiiiiiiiiHJijiiiiijji i i : 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ii 1 1 1 1 lllinilllHHII'iillil'C'", 1 1 ' 1 1 ! i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 II : I : ' " !! H1H IIIIHHH'HIl: »uiiilli>f!H'i unmiiii iiiiii ii iinHinmimuHiiiuiuii ll|l!IIM-:l|l u{HifiiluiUU { iMi"uiiu mil ii iiiiiiiiiiiiiniiiiiiiniiiniHinii)iniijiiiii llllllil lllllll 1 1 1 111 1 1 1 1 III : llll HIHHIIIHJII lillllll i i i j 1 1 1 i i i ii i i i I i 1 1 1 1 1 1 1 1 1 1 1 ) 1 1 1 1 1 1 1 1 1 1 j n 1 1 H n 1 1 1 ii 1 1 1 n! nil iiif iiiiiHiniiiiHiiiiiiii iiimiiHiim inii iniiiiii in ni iiini itiimiii iHifiiiiiinjiim fi '""mmimmimmiiHimniiiiiiHiHiHiiiiiiHuii uim imiiiiiiitniiiiHinmiiiHiiinin'ni'Hiit'imiHiijU! IHIHII, iiiiiiiiiiiiiiiiiiiiiiiiiiiiilii iii'iiiii niiiiiiliiii' iiimmiiimiiiiiiimiiiiiiiiiiiiili'iiiiniii'inHiii. fllllllllillll fitlillllUU IIIIIUH ^ parts in 100. Bearing this difference in mind all confusion will be avoided. CRITICAL POINTS The heating or cooling of steel does not proceed uniformly as there seems to be a lagging or retardation at certain temperatures. These are called critical points or critical temperatures and are caused by physical changes in the steel whereby heat is liberated 1553 1535 1515 1 ' / 4 C 3/ 1475 1155 "5 H35 h bo p 1195 L 1 \ i lc 2 " 1375 Ac[S , 1355 1335 1315 1295 1275 \ \ \ 1235 1215 1195 J \ Heating Curve Cooling Curve Fig. 9. — Critical point diagram. on cooling and is likewise absorbed in heating. According to Howe the changes occur at a lower temperature on cooling than on heating, unless the rates are infinitely slow. This is because of molecular inertia or lag. There are three principal critical points which are now usually designated as A h A 2 and A 3 , the first being the lowest. For the sake of distinguishing the different points, the heating or points of rising temperature, are designated asAc h Ac 2 and Ac 3 , STEEL MAKING 11 and the cooling points as Ar\, Ar% and Ar-s. While cooling through the lowest point there is a sufficient liberation of heat to show a glow in the dark and to actually raise the temperature to a slight degree. This is shown in Fig. 9, where the heating and cooling curves are marked so that decalescent and recalescent points can be seen. CLASSIFICATIONS OF STEEL Steel makers have no uniform classification for the various kinds of steel or steels used for different purposes. The following list shows the names used by some of the well-known makers: Air-hardening steel. Alloy steel Automobile steel Awl steel Axe and hatchet steel Band knife steel Band saw steel Butcher saw steel Chisel steel Chrome-nickel steel Chrome-vanadium steel Circular saw plates Coal augur steel Coal mining pick or cutter steel Coal wedge steel Cone steel Crucible cast steel Crucible machinery steel Cutlery steel Drawing die steel (Wortle) Drill rod steel Facing and welding steel Fork steel Gin saw steel Granite wedge steel Gun barrel steel Hack saw steel High-speed tool steel Hot-rolled sheet steel Lathe spindle steel Lawn mower knife steel Machine knife steel Magnet steel Mining drill steel Nail die shapes Nickel-chrome steel Paper knife steel Patent, bush or hammer steel Pick steel Pivot steel Plane bit steel Quarry steel Razor steel Roll turning steel Saw steel Scythe steel Shear knife steel Silico-manganese steel Spindle steel Spring steel Tool holder steel Vanadium tool steel Vanadium-chrome steel Wortle steel CHAPTER JI COMPOSITION AND PROPERTIES OF STEELS This deals with the compositions of steels used for the manu- facture of the various parts of intricate special machinery, especially airplane engines, requiring materials possessing unusually high tensile strength and shock-resisting qualities. A study of the many steel alloys in common use will enable the manufacturer to select from among their number a few brands embodying the particular qualities essential to his product, and by concentrating his attention upon them he may reduce the element of uncertainty and consequent hazard that must neces- sarily follow a wider range of selection. Most branches of the engineering trades are at one time or another faced with the necessity of reducing the weight of some piece of mechanism. This applies particularly to the manufac- ture of automobiles and airplanes and forms probably the chief reason for a thorough study of the nature and properties of the materials employed in the construction of such mechanisms. It is essential that the designer should have a full knowledge of the strength and durability of all the materials to be used, and it is important that those materials should be of a specified com- position and that the treatment should be checked by suitable tests in order that the results in actual practice shall correspond with the data on which the designer worked. Until about 1914, knowledge of the composition of aircraft steels and experience in their treatment was very limited; today there are so many brands of alloy steels requiring different treat- ment that great care must be exercised. As the hardening and tempering process is liable to error owing to the number of brands available, users are advised to choose as few types of steel as possible to cover their requirements. The treatment of the selected ones then quickly becomes familiar and the possibility of error is reduced. A range of about 10 steels will cover practically all require- ments. We give herewith the composition and properties of a range which may be chosen to advantage. 12 COMPOSITION AND PROPERTIES OF STEELS 13 As variation in heat treatment is required with different steels in order to obtain the best results it is necessary to consider the mechanical properties along with the chemical composition. It is possible, however, particularly in the case of nickel-chrome steels, to obtain widely varying results with varied heat treatment. The following table has been compiled from actual tests made with a particular make of nickel-chrome oil-hardening steel and illustrates this point very well: R.A. O.H. T. Time T.S. Per cent B.N, 825 650 30 59 57 269 S25 600 30 64 48 286 S25 550 30 69 42 321 825 500 30 75 43 332 825 450 30 85 42 375 825 450 20 87 49 364 825 400 30 96 38 41S 825 350 30 104 33 430 S25 ■ 200 15 121 38 512 825 not tempered 123 34 477 825 not tempered 126 21 512 800 not tempered 127 27 477 O.H. = Temperature in degrees Centigrade at which sample was hard- ened in oil. T. = Temperature in degrees Centigrade at which sample was temp- ered. Time = Time in minutes for tempering. T.S. = Tensile strength in tons per square inch given by test piece. R.A. = Reduction of area registered during above test. B.N. = Brinell hardness number. The material which gave the above tests when treated in the manner indicated forms the basis of a most interesting met- allurgical study and is of exceptional value in aircraft work. It will be noticed that various degrees of hardness can be obtained, and this factor is of special utility in the manufacture of articles where distortion is a disadvantage and at the same time difficult to avoid. The articles are first rough-machined and then heat-treated to a Brinell hardness of 250 to 321. At this hardness the articles can be machined and we then have no distortion in the finished goods as there is no subsequent heat treatment. It will thus be seen that it is possible to obtain widely varying results from one brand of steel, and it might also be said that it is possible to obtain 14 THE WORKING OF STEEL similar results from two steels of widely different chemical composition. It is advisable that the steel manufacturer should cooperate to a greater extent with the steel user to obtain a better understand- ing of the work which the finished article has to perform. Items subjected to different stresses require different materials and treatment, and in the case of resistance to wear it is well to bear in mind that a steel containing low proportions of nickel and chromium will resist wear better than a steel containing a high proportion of nickel and no chromium. It has become generally recognized that it is not only necessary to utilize materials of a sufficiently high yield point but the materials must also be of a nature suitable for resisting wear if the articles are subjected to abrasion and able to withstand shock if the articles are subjected to vibration. The advisability of putting samples of the materials through tests which bear some resemblance to the stresses which will be met in actual use is obvious, and in connection with airplane-engine manufacture this question has been given considerable attention. Perhaps the first decision to be reached in the manufacture of parts which are highly stressed is in relation to the composition of the materials employed. It will be understood that if the material should be of incorrect proportions satisfactory results can hardly be expected. It is expensive to introduce nickel, chromium, manganese and vanadium into mild steel, and unless the alloy thus produced is carefully watched its value may be destroyed as the result of incorrect proportions of carbon, sulphur and phosphorus. A full chemical analysis from time to time is necessary to preserve equality of product. In addition to the expense of manufacture, alloy steels require more careful treatment and a scientifically arranged system of checking temperatures is necessary if the results are to be relied upon. As the employment of these steels is necessary when we require an ultimate strength reaching to 130 tons per square inch the expense of materials and testing apparatus must be met. DIFFERENCE IN TREATMENT The alloys differ widely, and the treatment of these various alloy steels must be modified to suit each particular composition. When nickel is added to plain carbon steel the skin of the hard- COMPOSITION AND PROPERTIES OF STEELS 15 ened material is harder and the depth to which the quenching effect penetrates is greater. Chromium and tungsten added to plain carbon steel enable a more highly finished surface to be obtained when machining, and a finer grain is produced in the metal, but these elements do not appear to materially influence the hardness or the depth of case of the hardened material. Chrome-vanadium steels do not appear to have given quite as successful results as nickel-chrome steels, but for certain purposes they are preferable. Nickel is perhaps the most valuable element to the met- allurgist, and b}? - simply normalizing a bar of nickel steel to the same tensile strength as a sample of medium-carbon steel a comparison of the results readily establishes the superiority of the alloy steel. Increased elasticity is obtained and the impact- test figures are considerably improved, so that in cases where elasticitjr and shock-resisting qualities are required nickel steel is preferable, providing the carbon content is not excessive in proportion to the nickel. If the carbon content is not within the limits that will be specified later, the probability is that the article would fracture under a lighter load than would plain carbon steel. Bearing in mind the influence of these alloys when introduced into steel we can proceed to inquire into the composition of the materials, and it must be noted that it is necessary to maintain the proportions of the elements within certain limits in relation to each other. CARBON STEEL The use of plain carbon steel in aircraft work is quite restricted, as we generally require material able to withstand higher stresses; but it can be used for certain parts which are not subjected to great shock or wear, such as tachometer gear. It is then possible to use steel suitable for automatic machinery, and material of the following specification will be found to give satisfactory results : Per cent Carbon, not greater than 0. 25 Manganese, not greater than 0.85 Silicon, not greater than 0.20 Phosphorus, not greater than. 0.06 Sulphur, not greater than 0. 06 Should it be required to use a slightly higher tensile steel the following proportions will be found satisfactory, but machining 16 THE WORKING OF STEEL is more difficult and the tools will require more frequent attention: Per cent Carbon, not greater than . . 0.40 Manganese, not greater than 1 .00 Silicon, not greater than . 20 Phosphorus, not greater than 0.06 Sulphur, not greater than . 06 Neither of the above steels are suitable for case-hardening, but as they can be obtained in bright drawn bars the advantages of their use in all possible instances are obvious. Although case- hardening nickel steel has in many cases taken the place of case- hardening mild steel the latter is still used to a great extent in the manufacture of valve tappets, engine-timing gears, camshafts, gudgeon pins, etc. Parts made from this material present a good resistance to wear, and two qualities, low and medium car- bon, may be used with advantage. The low carbon will give a minimum of 23 tons breakiDg strength when normalized at 900 to 920°C. and the composition as follows: Per cent Carbon 0.10 Silicon 0.18 Manganese 0.60 Sulphur 0. 04 Phosphorus . 04 When this material is normalized as above, the physical tests should be as follows: Breaking strength 23 to 28 tons per square inch Yield ratio Not less than 50 per cent Elongation Not less than 30 per cent Reduction of area Not less than 50 per cent Brinell hardness 92 to 112 This material, if well made, will be found to case-harden well and uniformly, but it is frequently necessary to employ a similar steel with slightly improved breaking strength, although there is a tendency for the elongation to diminish. Another quality of case-hardening mild steel can be specified as follows: Per cent Carbon 0.15 Silicon 0.18 Manganese 0.75 Sulphur 0. 06 Phosphorus. . 06 COMPOSITION AND PROPERTIES OF STEELS 1 7 It will be noticed that higher proportions of sulphur and manganese are permissible in this instance. When the above material is normalized at 890 to 920°C. the following tests should be obtained: Tensile breaking strength 25 to 33 tons per square inch Yield ratio Not less than 50 per cent Elongation Not less than 25 per cent Reduction in area Not less than 50 per cent Brinell hardness 103 to 143 The normalizing temperatures given are within 50°C. above the critical temperature in each case. The carburizing should take place at 900°C, the length of time depending upon the depth of case required, and the articles should then be allowed to cool down in the compound. In order to refine the structure of the case the articles should be heated to about 870°C, and either allowed to cool in the air or be quenched in water. Finally they should be reheated to 780°C, and quenched in water to harden the case. With certain makes of steel not conforming correctly to the above specifications it may be necessary to depart very slightly from the above temperatures, but the most suitable conditions can readily be ascertained by trial and a little advice from the steel maker. There are many instances where it is necessary to have some knowledge of the properties of the core of case-hardened articles, and this can be obtained by putting test pieces through the same heat treatment and at the same time as the parts being manu- factured, and turning off the case to the depth to which the carbon has penetrated. It will generally be found that by the refining influence of the heat treatment the yield point and the breaking strength are improved and that the elongation and reduction of area are reduced. In some recent tests in connection with the last-named material the tests on the material as rolled and after the hardening treatment were: As rolled After treatment Breaking strength 31 tons 36 tons Yield point 21 tons 25 tons Elongation 28 per cent 23 per cent Reduction of area 58 per cent 51 per cent These figures are of value, as it must be realized that we cannot rely on the case to withstand shocks and our calculations must 18 THE WORKING OF STEEL consider the extent to which the material may be loaded, based on the strength of the core only. Should circumstances arise where it is necessary to employ material of higher ultimate strength and better surf ace- wearing qualities than the case-hardening carbon steels detailed above, use can be made of case-hardening nickel steels, and here it is necessary to exercise greater care in manufacture and heat treatment. LOW-NICKEL STEEL A good low-nickel alloy steel can be made up as follows: Per cent Carbon 0.13 Silicon 0.25 Manganese . 45 Sulphur 0.04 Phosphorus . 04 Nickel - 2.00 The phosphorus content must be carefully checked, for if excessive it will cause cold shortness, and attempts to straighten parts which may become distorted in hardening will result in fracture. Excess of sulphur produces hot shortness. This material when normalized at 850 to 900°C. should give the following results: Tensile breaking strength 25 to 35 tons per square inch Yield ratio Not less than 55 per cent Elongation Not less than 30 per cent Reduction of area Not less than 55 per cent Brinell hardness 103 to 153 A step higher in tensile breaking strength and yield ratio can be obtained with an alloy steel containing a larger proportion of nickel and the elongation will remain about the same. A chemical analysis of such a steel should show the results given below, and the necessity for maintaining a low proportion of the injurious elements renders the manufacture of this steel somewhat difficult and consequently expensive: Per cent Carbon 0.15 Silicon 0.18 Sulphur 0.04 Phosphorus . 04 Manganese 0.35 Nickel 5.00 The case-hardening nickel steels given above are suitable for articles where a good, hard wearing surface is necessary, but COMPOSITION AND PROPERTIES OF STEELS 19 when quenching to harden the case it is necessary to reheat to a somewhat lower temperature than is the case with carbon steels. When it is decided which brand of material to use it is advisable to carry out a series of tests to ascertain the most suitable temperature. Occasionally it is necessary to manufacture articles where good wearing qualities are required, but the parts are so thin that a hard case would be disastrous as there would be no core left. In such instances an alloy steel containing about 3 per cent nickel, 0.30 per cent carbon and about 0.70 per cent manganese will be found of great value as it is thus possible to obtain 45 tons per square inch ultimate stress and a Brinell hardness of about 200. The materials which have probably been of greatest value to the automobile manufacturer engaged on airplane-engine work are probably the alloy steels containing nickel and chromium in their composition. These alloys can be so constructed that they can first be hardened and then tempered to give almost any degree of hardness between 250 and 500 Brinell, and it is not a difficult matter to bring the hardness to about 320 Brinell. Up to this figure the material can be machined and the parts will stand a great deal of shock and wear, but should the hardness be greater the probability is that the further machining would be impossible. It must not be concluded from the above remarks that the Brinell-hardness numeral can be taken as a general guide to the machining properties of materials, but in comparing two samples of the same steel it can be taken as a rough indication. When comparing different alloys it is quite possible that one steel can easily be cut by another which registers lower on Brinell test. The addition of nickel in excess of 1.5 per cent increases the toughness and difficulty in machining. A high-tensile nickel-chrome steel, suitable for tempering to various degrees of hardness can be built up as follows: Per cent Carbon 0.20 to 0.30 Silicon Not over . 30 Manganese . 35 to . 60 Sulphur Not over 0. 04 Phosphorus Not over 0. 04 Nickel 2 . 75 to 3 . 50 Chromium . 45 to . 75 20 THE WORKING OF STEEL If the above material be heated up to 820°C, quenched in whale oil and then tempered at 600°C. the test results should be approximately: Tensile breaking strength. : Not less than 45 tons per square inch Yield ratio Not less than 75 per cent Elongation Not less than 15 per cent Reduction of area. ... Not less than 50 per cent Brinell-hardness number 179 •- 50 cO 4.0 <4- 36 Q ra f h-r » .B Qr 01 Pi' l - E ^_ 1 150 200 250 300 350 400 45C Brinell Hardness Mumber Fig. 10.— Relation of Brinell hardness to tensile strength. When using this material for a high-tensile strain and a hardness of about 320 Brinell, as previously suggested, it is an advantage to rough out the parts before heat-treating so that very little metal is left for removing in the hard state. In connection with hardness and ultimate strength we often find attempts made to establish a law in which the two qualities COMPOSITION AND PROPERTIES OF STEELS 21 are related. It is not correct to look upon the Brinell-hardness test as a measure of tensile strength when comparing materials of different composition, but when comparing the same brand of material treated to different degrees of hardness there is reasonably close connection between that hardness and the ultimate strength of the material in the same state. Some elaborate tests were made to ascertain this relation in the case of an alloy steel containing a moderate proportion of nickel and chromium, and by plotting the results of a Brinell test and tensile test on various heat-treated samples the chart shown in Fig. 10 was prepared. For that particular quality of material it was found possible to ascertain the tensile strength with a reasonable degree of accuracy after simply measuring the diameter of the impression left by a 10-mm. ball under a pressure of 3,000 kg. on the Brinell machine. It is simply necessary to locate on axis OA the position indicating the impression diameter in millimeters, and from that point travel horizontally to the curve in graph D, then vertically across axis OB to the curve in graph E and by traveling horizontally to axis OC we obtain the approximate tensile strength. SOME OF THE NAMES USED Steel makers and metallurgists use names which are not so familiar to steel users. Among these and most commonly used are "ferrite," "cementite" and "pearlite." Ferrite, according to Howe, is now employed to designate that part of iron or steel containing no carbide (or only a trace) in solid solution. Cemen- tite is the mixture of iron and carbon in the proportion of 93.4 per cent iron and 6.6 per cent carbon. It is also known as a carbide of iron and has the symbol of Fe 3 C, which means that it is composed of 3 atoms of iron and 1 atom of carbon. Pearlite contains approximately 0.9 per cent of carbon and is found in inter-stratified layers or in bands of cementite and ferrite. It is considered as a separate constituent of steel and is called pearlite on account of its having the appearance of mother of pearl when examined under a microscope. Steel of this mixture forms a special class and is known as "eutectic" steel while steels containing less than this proportion of carbon (0.9 per cent) are called " hypo-eutectic steels." These steels however contain certain known amounts of pearlite and of free or excess ferrite. 22 THE WORKING OF STEEL Steels are divided according to their carbon content into three classes: hypo-eutectoid, below 0.89 per cent carbon; eutectoid, at 0.89 per cent; and hyper-eutectoid above 0.89 per cent. The hypo-eutectic class will cover most of the airplane steels. The medium-carbon steel is a good illustration. This material is generally in an annealed condition to start with, or a mixture of ferrite and pearlite. As heat is applied and the steel passes the A 3 point, the constituents go into a solid solution consisting of iron carbide, cementite or a double carbide of iron and the special element (Cr, Va) in gamma iron. If this is quenched in salt water or other abrupt medium, it is called austenite, but if quenched in oil, probably martensite, which is a more stable form resulting from the austenite giving way along its cleavage planes. On heating or drawing marten- site, there is a slight precipitation of ferrite or beta iron. This mixture consisting of beta iron and a solid solution of carbide in gamma iron is called troosite which becomes sorbite on further drawing or on a further precipitation of beta iron. At the Ac% point the beta iron is converted into alpha iron and on the drawing being continued the gamma solution approaches the eutectic until at the Ac x point it is converted into pearlite. The mixture now consists of ferrite and pearlite. Annealing. — The object of annealing is to relieve strains and to soften the structure or make it normal. It consists in raising the steel to a temperature above the Ac% point and holding it a sufficient time to get a complete solid solution. Then allowing it to cool slowly in the furnace in order that all transformation .may be completed — austenite, martensite, troosite, sorbite and ending with a mixture of ferrite and pearlite. This is a furnace or soft anneal. Most annealing or better "normalizing" is done by merely heating past the Ac% point and then cooling in air. This gives a mixture of ferrite and sorbite instead of ferrite and pearlite as results in furnace cooling. If a fine structure is wanted coincidentally in a good soft material, quench at above the Acz point and draw at just below the Ac x point. Quenching. — -Materials are quenched in order to get maximum hardness and grain refinement. It consists in heating the steel past its Ac% point and quenching in oil or water. This retains it in its austenitic and martensitic condition which is very hard and fine. COMPOSITION AND PROPERTIES OF STEELS 23 Drawing. — Drawing consists in heating to some point below Aci and cooling in air or oil. This is a softening or toughening process in which ferrite is liberated varying with the increase of draw. Practically all of these steels on being drawn are sorbitic. Grain Size. — Care should be exercised in not passing the upper critical too far, as the grain size grows accordingly and there is danger of overheating. Overheating. — This causes a very coarse structure but it can be restored by merely heating to a little above the critical (upper) point and quenching. Overheating should not be confounded with burning. Burning. — Burnt steel is brittle and its fracture is coarse and shiny. -Material that has been burnt is of no value in this work. Test Specimens. — All specimens that are heat-treated for test purposes are carefully machined to the required shape and size, then treated in electric or oil furnaces. Much attention should be paid to the machining of specimens, as an extra deep cut will spoil the test. This often occurs near the shoulder. The data from a poor specimen are of no value. CHAPTER III ALLOYS AND THEIR EFFECT UPON STEEL In view of the fact that alloy steels are coming into a great deal of prominence, it would be well for the users of these steels to fully appreciate the effects of the alloys upon the various grades of steel. We have endeavored to summarize the effect of these alloys so that the users can appreciate their effect, without having to study a metallurgical treatise and then, perhaps, not get the crux of the matter. NICKEL Nickel may be considered as the toughest among the non-rare alloys now used in steel manufacture. Originally nickel was added to give increased strength and toughness over that obtained with the ordinary rolled structural steel and little attempt was made to utilize its great possibilities so far as heat treatment was concerned. The difficulties experienced have been a tendency towards laminated structure during manufacture and great liability to seam, both arising from a non-homogeneous melting. When extra care is exercised in the manufacture, particularly in the melting and rolling, many of these difficulties can be overcome. The electric steel furnace, of modern construction, is a very important step forward in the melting of nickel steel; neither the crucible process nor basic or acid open hearth furnaces give such good results. It is also necessary that small ingots be made so as to cut out piping. Great care must be exercised in reheating the billet for rolling so that the steel is correctly soaked. The rolling must not be forced; too big reduction per pass should not be indulged in, as this sets up a tendency towards seams. Nickel steel has remarkably good mechanical qualities when suitably heat-treated, and it is preeminently adapted for case- hardening. It is not difficult to machine low-nickel steel, consequently it is in great favor where easy machining properties are of importance. 24 ALLOYS AND THEIR EFFECT UPON STEEL 25 Nickel influences the strength and ductility of steel by being dissolved directly in the iron or ferrite; in this respect differing from chromium, tungsten and vanadium. The addition of each 1 per cent nickel up to 5 per cent will cause an approximate increase of from 4,000 to 6,000 lb. per square inch in the tensile strength and elastic limit over the corresponding steel and without any decrease in ductility. The static strength of nickel steel is affected to some degree by the percentage of carbon; for instance, steel with 0.25 per cent carbon and 3.5 per cent nickel has a tensile strength, in its normal state, equal to a straight carbon steel of 0.5 per cent with a proportionately greater elastic limit and retaining all the advantages of the ductility of the lower carbon. To bring out the full qualities of nickel it must be heat-treated, otherwise there is no object in using nickel as an alloy with carbon steel as the additional cost is not justified by increased strength. Nickel has a peculiar effect upon the critical ranges of steel, the critical range being lowered by the percentage of nickel; in this respect it is similiar to carbon only more marked. Generally speaking, nickel steel requires a lower heat-treating temperature than chrome steel or tungsten steel, being very similar to manga- nese in this respect. Nickel can be alloyed with steel in various percentages, each percentage having a very definite effect on the microstructure. For instance, a steel with 0.2 per cent carbon and 2 per cent nickel has a pearlitic structure but the grain is much finer than if the straight carbon were used. With the same carbon content and say 5 per cent nickel, the structure would still be pearlitic, but much finer and denser, therefore capable of withstanding shock, and having greater dynamic strength. With about 0.2 per cent carbon and 8 per cent nickel, the steel is nearing the stage between pearlite and martensite, and the structure is extremely fine, the Ferrite and pearlite having a tendency to orientiate, as seen in a purely martensite structure. Steel with 0.2 per cent carbon and 15 per cent nickel is entirely martensite. Higher percentages of nickel change the martensite structure to austenite, the steel then being non-magnetic. The higher percentages, that is 30 to 35 per cent nickel, are used for valve seats, valve heads, and valve stems, as the alloy is a poor conductor of heat and is particularly free from any tendency towards corrosion or pitting from the action of waste gases of the internal-combustion engine. 4 26 THE WORKING OF STEEL To obtain the full effect of nickel as an alloy, it is essential that the correct percentage of carbon be used. High nickel and low carbon will not be more efficient than lower nickel and higher carbon, but the cost will be much greater. Generally speaking, heat-treated nickel alloy steels are about two to three times stronger than the same steel annealed. This point is very im- portant as many instances have been found where nickel steel is incorrectly used, being employed when in the annealed or normal state. CHROMIUM Chromium when alloyed with steel, has the characteristic function of opposing the disintegration and reconstruction of cementite. This is demonstrated by the changes in the critical ranges of this alloy steel taking place slowly; in other words, it has a tendency to raise the Ac range (decalescent points) and lower the Ar range (recalescent points). Chromium steels are therefore capable of great hardness, due to the rapid cooling being able to retard the decomposition of the austenite. The great hardness of chromium steels is also due to the forma- tion of double carbides of chromium and iron. This condition is not removed when the steel is slightly tempered or drawn. This additional hardness is also obtained without causing undue brittleness such as would be obtained by any increase of carbon. The degree of hardness of the lower-chrome steels is dependent upon the carbon content, as chromium alone will not harden iron. The toughness so noticeable in this steel is the result of the fineness of structure; in this instance, the action is similar to that of nickel, and the tensile strength and elastic limit is therefore increased without any loss of ductility. We then have the desirable condition of tough hardness, making chrome steels extremely valuable for all purposes requiring great resistance to wear, and in higher-chrome contents resistance to corrosion. All chromium-alloy steels offer great resistance to corrosion and erosion. In view of this, it is surprising that chromium steels are not more largely used for structural steel work and for all purposes where the steel has to withstand the corroding action of air and liquids. Bridges, ships, steel building, etc., would offer greater resistance to deterioration through rust if the chromium- alloy steels were employed. Prolonged heating and high temperatures have a very bad effect upon chromium steels. In this respect they differ from ALLOYS AND THEIR EFFECT UPON STEEL 27 nickel steels, which are not so affected by prolonged heating, but chromium steels will" stand higher temperatures than nickel steels when the period is short. Chromium steels, due to their admirable property of increased hardness, without the loss of ductility, make very excellent chisels and impact tools of all types, although for die blocks they do not give such good results as can be obtained from other alloy combinations. For ball bearing steels, where intense hardness with great toughness and ready recovery from temporary deflection is re- quired, chromium as an alloy offers the best solution. Two per cent chromium steels, due to their very hard tough surface, are largely used for armor-piercing projectiles, cold rolls, crushers, drawing dies, etc. The normal structure of chromium steels, with a very low car- bon content is roughly pearlitic up to 7 per cent, and martensitic from 8 to 20 per cent; therefore, the greatest application is in the pearlitic zone or the lower percentages. NICKEL-CHROMIUM A combination of the characteristics of nickel and the char- acteristics of chromium, as described, should obviously give a very excellent steel as the nickel particularly affects the ferrite of the steel and the chromium the carbon. From this combina- tion, we are able to get a very strong ferrite matrix and a very hard tough cementite. The strength of a strictly pearlitic steel over a pure iron is due to the pearlitic being a layer arrangement of cementite running parallel to that of a pure iron layer in each individual grain. The ferrite i.e., the iron is increased in strength by the resistance offered by the cementite which is of the staple iron carbon combination or carbide known as Fe3c. The cemen- tite, although adding to the tensile strength, is very brittle and the strength of the pearlite is the combination of the ferrite and cementite. In the event of the cementite being strengthened, as in the case of strictly chromium steels, an increased tensile strength is readily obtained without loss of ductility .and if the ferrite is strengthened then the tensile strength and ductility of the metal is still further improved. Nickel-chromium alloy represents one of the best combinations available at the present time. The nickel intensifies the physical characteristics of the chromium and the chromium has a similar effect on the nickel. 23 the Working of sVeeL For case-hardening, nickel-chromium steels seem to give very excellent results. The carbon is very rapidly taken up in this combination, and for that reason is rather preferable to the straight nickel steel. With the mutually intensifying action of chromium and nickel there is a most suitable ratio or these two alio; s, nd it has been found that roughly 2^ parts of nickel to about 1 part of chro- mium gives the best results. Therefore, we have the standard types of 3.5 per cent nickel with 1.5 per cent chromium to 1.5 per cent nickel with 0.6 per cent chromium and the various intermediary types. This ratio, however, does not give the whole story of nickel-chromium combinations, and many surprising results have been obtained with these alloys when other percen- tage combinations have been employed. VANADIUM Vanadium has a very marked effect upon alloy steels rich in chromium, carbon, or manganese. Vanadium itself, when combined with steel very low in carbon, is not so noticeably beneficial as the same carbon steel higher in manganese, but if a small quantity of chromium is added, then the vanadium has a very marked dynamic effect. Therefore, it would seem that vanadium has the effect of intensifying the action of chromium and manganese, or that vanadium is intensified by the action of chromium or manganese. Vanadium has the peculiar property of readily combining with ferrite, also the carbon forming carbides and is to be found in solid solution in the ferrite. The ductility of carbon-vanadium steels is therefore increased, likewise the ductility of chrome- vanadium steels. The full effect of vanadium is not felt unless the temperatures, to which the steel is heated for hardening, are raised considerably. It is therefore necessary that a certain amount of soaking takes place, so as to get the necessary equalization. This is true of all cementitic compounds, of which vanadium is one. Chrome-vanadium steels also have a tendency for greater depth of hardening and anti-fatigue properties than can be obtained from straight chromium steels. It would appear that the intensification of the chrome and manganese in the alloy steel accounts for this peculiar phenomenon. Vanadium is also a very excellent scavenger for either remov- ALLOYS AND THEIR EFFECT UPON STEEL 29 ing the harmful gases, or causing them to enter into solution with the metal in such a way as to largely obviate their harmful effects. Chrome-vanadium steels have been claimed, by many steel manufacturers and users, to be preferable to nickel-chrome steels. While not wishing to pass judgment on this, it should be borne in mind that the chrome-vanadium steel, which is tested, is generally compared with a very low nickel-chromium alloy steel (the price factor entering into the situation) , but equally good results can be obtained by nickel-chromium steels of suitable analysis. Where price is the leading factor, there are many cases where a stronger steel can be obtained from the chrome and vanadium than the nickel-chrome. It will be safe to say that each of these two systems of alloys have their own particular fields and chrome-vanadium steel should not be regarded as the sole solu- tion for all problems, neither should nickel-chromium. MANGANESE Manganese adds considerably to the tensile strength of steel, but this is dependent on the carbon content. High carbon ma- terially adds to the brittleness, whereas low-carbon, pearlitic- manganese steels are very tough and ductile and are not at all brittle, providing the heat-treating is correct. Manganese steel is very susceptible to high temperatures and prolonged heating. Low-carbon pearlitic-manganese steel is a very efficient steel, but its efficiency is entirety dependent on the temperature to which it is heated for hardening, or the temperature used for annealing. Low-carbon pearlitic-manganese steel made in the electric furnace seems to be more efficient than the same chemical analysis steel made by either the open hearth or crucible process. No reason has as yet been assigned for this peculiar phenomenon, but it is believed that the removal of the harmful gases, particu- larly oxygen and nitrogen, is responsible. Manganese when added to steel has the effect of lowering the critical range ; 1 per cent manganese will lower the upper critical point 60°F. The action of manganese is very similar to that of nickel in this respect, only twice as powerful. As an instance, 1 per cent nickel would have the effect of lowering the upper critical range from 25 to 30°F. Low-carbon pearlitic-manganese steel, heat-treated, will give dynamic strength which cannot be equalled by low-priced and 30 THE WORKING OF STEEL necessarily low-content nickel steels. In many instances, it is preferable to use high-grade manganese steel, rather than low- content nickel steel. High-manganese steels or austenite manganese steels are used for a variety of purposes where great resistance to abrasion is required, the percentage of manganese being from 11 to 14 per cent, and carbon 1 to 1.5 per cent. This steel is practically valueless unless heat-treated; that is, heated to about yellow red and quenched in ice water. The structure is then austenite and the air-cooled structure of this steel is martensite. Therefore this steel has to be heated and very rapidly cooled to obtain the ductile austenite structure. Manganese between 2 and 7 per cent is a very brittle material when the carbon is about 1 per cent or higher and is, therefore, quite valueless. Below 2 per cent manganese steel low in carbon is very ductile and tough steel. The high-content manganese steels are known as the "Had- field manganese steels," having been developed by Sir Robert Hadfield. Small additions of chrome up to 1 per cent increase the elastic limit of low-carbon pearlitic-manganese steels without affecting the steel in its resistance to shock, but materially decrease the percentage of elongation. Vanadium added to low-carbon pearlitic manganese steel has a very marked effect, increasing greatly the dynamic strength and changing slightly the susceptibility of this steel to heat treatments, giving a greater margin for the hardening tempera- ture. Manganese steel with added vanadium is most efficient when heat-treated. TUNGSTEN Tungsten, as an alloy in steel, has been known and used for a long time. The celebrated and ancient damascus steel being a form of tungsten-alloy steel. Tungsten and its effects, however, did not become generally realized until Robert Mushet experi- mented and developed his famous mushet steel and the many improvement made since that date go to prove how little Mushet himself understood the peculiar effects of tungsten as an alloy. Tungsten acts on steel in a similar manner to carbon, that is, it increases its hardness, but is much less effective than carbon in this respect. If the percentage of tungsten and manganese is ALLOYS AND THEIR EFFECT UPON STEEL 31 high, the steel can be hardened by cooling in the air. This effect is directly opposite to that of carbon. It was this com- bination that Mushet used in his well-known steel. The principal use of tungsten is in high-speed tool steel, but here a high percentage of manganese is distinctly detrimental, making the steel liable to fire crack, very brittle, and weak in the body, less easily forged and annealed. Manganese should be kept low and a high percentage of chromium steel used instead. The tungsten-chromium steels, when hardened, retain their hardness, even when heated to a dark cherry red by the friction of the cutting or the heat arising from the chips. This charac- teristic led to the term "red hardness" being applied to this class of steel, and it is this property that is responsible for the increase of cutting speeds in the tungsten-chrome alloy, that is high-speed steel. Tungsten when added to steel up to 6 per cent does not have the property of red hardness any more than carbon tool steel, providing the manganese or chromium is low. Tungsten has a rapidly increasing cutting efficiency up to 13 per cent, thereafter falling until 14 per cent, then increasingly efficient until 18 per cent or more is used. If chromium is alloyed with tungsten, then a very definite red- hard effect is noticed with a great increase of cutting efficiency. The maximum red-hard cutting efficiency of the tungsten, chrome steel seems to be a definite chemical analysis ratio. But there are various mechanical and other reasons why this ratio is not used for high-speed steel, as high-chromium content steel is very easily spoiled by the high heats necessary in its heat treatment. Very little is known of the actual function of tungsten, al- though a vast amount of experimental work has been done. It is possible that when the effect of tungsten with iron carbon alloys is better known, a greater improvement can be expected from these steels. Tungsten has been tried and is still used by some steel manufacturers for making punches, chisels, and other impact tools. It has also been used for springs, and has given very good results, although other less expensive alloys give equally good results, and are in some instances, better. Tungsten is largely used in permanent magnets. In this, its action is not well understood. In fact, the reason why steel becomes a permanent magnet is not at all understood. Theories have been evolved, but all are open to serious questioning. The 32 THE WORKING OF STEEL principal effect of tungsten, as conceded by leading authorities, is that it distinctly retards separation of the iron-carbon solution, removing the lowest recalescent point down to atmospheric temperature. A peculiar property of tungsten, when used in the iron-carbon alloys, is that if a temperature of 1,750°F. is not exceeded, it does not interfere with the carbide change, nor affect the tempera- tures of the recalescent points. But when the hardening tem- perature is raised above 1,850°F., a most remarkable effect is conveyed upon the falling transformation points, prevent- ing their formation entirely, down to about the atmospheric temperature. The lowering of the carbide change, which is produced by heating tungsten steels to over 1,850°F., is the real cause of the red-hard properties of these alloys, is not understood, and there is no direct evidence to show what actually happens at these high temperatures. There is every reason to believe that when the tungstide Fe2W is present, it gradually goes into solution as the tempera- ture is raised above 1,550°F., the amount of compound present being higher as the tungsten is increased. When completely in solution, the temperature of the carbide change (recalescent point) is lowered on cooling. It is quite an open question, how- ever, whether this lowering is entirely due to the Fe2W in solution, or whether some other chemical change also occurs. At a temperature above 1,850°F., there may be chemical reactions between the iron and tungsten carbide, which give a new compound, resulting in the disappearance of the critical point of the falling temperature 1,300°F., and the appearance of another point at a lower temperature. Other combinations, in which there should be no free tungstide of iron, give the same lowering of the carbide change after heating to high tempera- tures; therefore, the subject is still surrounded with a fair amount of uncertainty. MOLYBDENUM Molybdenum possesses the same characteristics as tungsten, but on account of its scarcity, is not used a great deal for com- mercial purposes. It is about twice as heavy and twice as effective as tungsten, and is supposed to harden at a little less temperature, but from tests made, nothing has been published showing its advantage over tungsten. ALLOYS AND THEIk EFFECT UPON STEEL 33 SILICON Silicon prevents, to a large extent, defects such as air bubbles or blow holes forming pockets while steel is melting, as it mixes with the gases and oxide. When present in 1 per cent or more, it adds a great resiliency to steel, and in combination with either chrome, vanadium, or manganese, with a predominant carbon contents for element selected, it makes a splendid spring, and is used largely for its ability to absorb shocks. PHOSPHORUS Phosphorus is one of the impurities in steel, and it has been the object of steel makers for years to eliminate it. On cheap grades of steel, not subject to any abnormal strain or stress, 0.1 per cent phosphorus is not objectionable, and will help machine ability by acting as a lubricant. High phosphorus has a tendency to make steel "cold short," i.e., low forging heats are apt to make checks or to start seams, and is also subject to cracking or opening up under sudden quenching. SULPHUR Sulphur is another impurity and high sulphur is even a greater detriment to steel than phosphorus. High sulphur up to 0.09 per cent helps machining properties, but has a tendency to make the steel "hot short," i.e., subject to opening up cracks and seams at forging or rolling heats. Unless used in combination with manganese on commercial steel, sulphur should never exceed 0.06 per cent and phosphorus over 0.08 per cent. Steel used for tool purposes should have as low phosphorus and sulphur contents as possible, not over 0.02 per cent, which can readily be made in both crucible and electric furnaces. We can sum up the various factors something as follows for ready reference. The ingredient Its effect Iron The basis of steel Carbon The determinative Sulphur A strength sapper Phosphorus The weak link Oxygen A strength destroyer Manganese For strength Nickel For strength and toughness Tungsten Hardener and heat resister Chromium For resisting shocks 3 34 THE WORKING OF STEEL The ingredient Its effect Vanadium Purifier and fatigue resister Silicon Impurity and hardener Titanium ■ Removes nitrogen and oxygen Molybdenum Hardener and heat resister Aluminum Kills or deoxidizes steel PROPERTIES OF ALLOY STEELS The following table shows the percentages of carbon, manga- nese, nickel, chromium and vanadium in typical steel alloys for engineering purposes. It also gives the elastic limit, tensile strength, elongation and reduction of area of the various alloys, all being given the same heat treatment with a drawing tem- perature of 1,100°F. (600°C). The specimens were one inch rounds, machined after heat treatment. Tungsten is not shown in the table because it is seldom used in engineering construction steels and then usually in combination with chromium. Tungsten is used principally for the magnets of magnetos, to some extent in the manufacture of hacksaws, and for special tool steels. Table 1. — Properties of Alloy Steels a! O o Manganese, per cent 2 a a ° C o o u 3 a B 4» .3 s 03 g a - .5 1 £ ' o S3 "^3 a Tensile strength, lb. per sq. in. ■H a j: J.s 3 IN "o a ^ 03 0.27 0.55 49,000 80,000 30 65 0.27 0.47 0.26 66,000 98,000 25 52 0.36 0.42 58,000 90,000 27 '60 ,0 . 34 0.87 0.13 82,500 103,000 22 57 0.45 0.50 65,000 96,000 22 52 0.43 0.60 0.32 96,000 122,000 21 52 0.47 0.90 0.15 102,000 127,500 23 58 0.30 0.60 3.40 75,000 105,000 25 67 0.33 0.63 3.60 0.25 118,000 142,000 17 57 0.30 0.49 3.60 L.70 119,000 149,500 21 60 0.25 0.47 3.47 1.60 0.15 139,000 170,000 18 53 0.25 0.50 2.00 LOO 102,000 124,000 25 70 [0.38 0.30 2.08 1.16 120,000 134,000 20 57 0.42 0.22 2.14 L.27 0.26 145,000 161,500 16 53 0.36 0.61 1.46 ( ).64 117,600 132,500 16 58 0.36 0.50 1.30 ( ).75 0.16 140,000 157,500 17 54 0.30 0.50 ( ).80 90,000 105,000 20 50 0.23 0.58 ( ).82 0.17 106,000 124,000 21 66 0.26 0.48 ( ).92 0.20 112,000 137,000 20 61 0.35 0.64 L.03 0.22 132,500 149,500 16 54 0.50 0.92 .02 0.20 170,000 186,000 15 45 ALLOYS AND THEIR EFFECT UPON STEEL 35 NON-SHRINKING, OIL-HARDENING STEELS Certain steels have a very low rate of expansion and con- traction in hardening and are very desirable for test plugs, gages, punches and dies, for milling cutters, taps, reamers, hard steel bushings and similar work. It is recommended that for forging these steels it be heated slowly and uniformly to a bright red, but not in a direct flame or blast. Harden at a dull red heat, about 1,300°F. A clean coal or coke fire, or a good muffle-gas furnace will give best results. Fish oil is good for quenching although in some cases warm water will give excellent results. The steel should be kept moving in the bath until perfectly cold. Heated and cooled in this way the steel is very tough, takes a good cutting edge and has very little expansion or contraction which makes it desirable for long taps where the accuracy of lead is important. The composition of these steels is as follows: Per cent Manganese 1 . 40 to 1 . 60 Carbon . 80 to . 90 Vanadium 0.20 to 0.25 £ g c S g Ft. Lb. Per Sq. In. Cliarpy Test BrineH So. Average \ie!d Point, Average Ultimate Strength, Lb. Per Sq. In. Thousands Fig. 11. — Effect of copper in steel. EFFECT OF A SMALL AMOUNT OF COPPER IN MEDIUM-CARBON STEEL This shows the result of tests by C. R. Hay ward and A. B. Johnston on two types of steel: one containing 0.30 per 36 THE WORKING OF STEEL cent carbon, 0.012 per cent phosphorus, and 0.860 per cent copper, and the other 0.365 per cent carbon, 0.053 per cent phosphorus, and 0.030 per cent copper. The accompanying chart in Fig. 11 shows that high-copper steel has decided supe- riority in tensile strength, yield point and ultimate strength, while the ductility is practically the same. Hardness tests by both methods show high-copper steel to be harder than low-copper, and the Charpy shock tests show high-copper steel also superior to low-copper. The tests confirm those made by Stead, showing that the behavior of copper steel resembles that of nickel steel. The high-copper steels show finer grain than the low-copper. The quenched and drawn specimens of high-copper steel were found to be slightly more martensitic. HIGH-CHROMIUM OR RUST-PROOF STEEL High-chromium, or what is called stainless steel containing from 11 to 14 per cent chromium, was originally developed for cutlery purposes, but has in the past few years been used to a considerable extent for exhaust valves in airplane engines because of its resistance to scaling at high temperatures. Percentage Carbon 0.20 to 0.40 Manganese, not to exceed . 50 Phosphorus, not to exceed ■. 0. 035 Sulphur, not to exceed 0. 035 Chromium 11.50 to 14.00 Silicon, not to exceed 0. 30 The steel should be heated slowly and forged at a temperature above 1,750°F. preferably between 1,800 and 2,200°F. If forged at temperatures between 1,650 and 1,750°F. there is considerable danger of rupturing the steel because of its hardness at red heat. Owing to the air-hardening property of the steel, the drop- forgings should be trimmed while hot. Thin forgings should be reheated to redness before trimming, as otherwise they are liable to crack. The forgings will be hard if they are allowed to cool in air. This hardness varies over a range of from 250 to 500 Brinell, depending on the original forging temperature. Annealing can be done by heating to temperatures ranging from 1,290 to 1,380°F. and cooling in air or quenching in water or oil. After this treatment the forgings will have a hardness of ALLOYS AND THEIR EFFECT UPON STEEL 37 about 200 Brinell and a tensile strength of 100,000 to 112,000 lb. per square inch. If softer forgings are desired they can be heated to a temperature of from 1,560 to 1,G50°F. and cooled very slowly. Although softer the forgings will not machine as smoothly as when annealed at the lower temperature. Hardening. — The forgings can be hardened by cooling in still air or quenching in oil or water from a temperature between 1,650 and 1,750°F. The physical properties do not vary greatly when the carbon is within the range of composition given, or when the steel is hardened and tempered in air, oil, or water. When used for valves the following specification of physical properties have been used: Yield point, pounds per square inch 70,000 Tensile strength, pounds per square inch 90,000 Elongation in 2 in., per cent 18 Reduction of area, per cent 50 The usual heat treatment is to quench in oil from 1,650°F. and temper or draw at 1,100 to 1,200°F. One valve manufac- turer stated that valves of this steel are hardened by heating the previously annealed valves to 1,650°F. and cooling in still air. This treatment gives a scleroscope hardness of about 50. In addition to use in valves this steel should prove very satis- factory for shafting for water-pumps and other automobile parts subject to objectionable corrosion. Table 2. — Comparison op Physical Properties for High-chromium Steels of Different Carbon Content C 0.20 C 0.27 Mn 0.45 Mn 0.50 Cr 12.56 Cr 12.2-1 C 0.50 Cr 14.84 Quenched in oil from degrees Fah- renheit 1,600 Tempered at degrees Fahrenheit. . . 1,160 Yield point, pounds per square inch . 78,300 Tensile strength, pounds per square inch 104,600 Elongation in 2 in., per cent 25.0 Reduction of area, per cent 52.5 1,600 1,650 1,080 1,100 75,000 91,616 104,250 123,648 23.5 14.5 51.4 33.5 38 THE WORKING OF STEEL Table 3. — Comparison of Physical Properties between Air, Oil and Water-hardened Steel Having Chemical Analysis in Percentage op Carbon 0.24 Manganese 0.30 Phosphorus 0. 035 Sulphur . 035 Chromium 12.85 Silicon 0.20 Hardening medium Hardened from, degrees Fahrenheit Tempered at, degrees Fahrenheit Elastic limit, lb. per sq. in. Tensile strength, lb. per sq. in. Elonga- tion in 2 in. per cent Reduc- tion of area, per cent Air 1,650 ■ 930 1,100 1,300 1,380 1,470 158,815 99,680 70,785 66,080 70,785 192,415 120,065 101,250 98,335 96,990 13.0 21.0 26.0 28.0 27.0 40.5 59.2 64.6 63.6 64.7 Oil 1,650 930 1,100 1,300 i 1,380 163,070 88,255 77,950 88,255 202,720 116,480 105,505 98,785 8.0 20.0 25.5 27.0 18.2 56.9 63.8 66.3 Water. . . . 1,650 930 1,100 1,300 . 1,380 158,815 90,270 66,080 67,200 202,050 120,735 102,590 97,890 12.0 22.0 25.8 27.0 34.2 59.8 64.8 65.2 This steel can be drawn into wire, rolled into sheets and strips and drawn into seamless tubes. Corrosion. — This steel like any other steel when distorted by cold working is more sensitive to corrosion and will rust. Rough cut surfaces will rust. Surfaces finished with a fine cut are less liable to rust. Ground and polished surfaces are . practically immune to rust. When chromium content is increased to 16 to 18 per cent and silcon is added, from 2 to 4 per cent, thus steel becomes rust proof in its raw state, as soon as the outside surface is removed. It does not need to be heat-treated in any way. These composi- tions are both patented. ALLOYS AND THEIR EFFECT UPON STEEL 39 S. A. E. STANDARD STEELS The following steel specifications are considered standard by the Society of Automotive Engineers and represents automobile practice in this country. These tables give the S. A. E. number, the composition of the steel and the heat treatment. These are referred to by letter — , the heat treatments being given in detail on pages 134 to 137 in Chapter 8. It should be noted that the percentage of the different ingredients desired, is the mean, or halfway between the minimum and maximum. Table 4.— -Carbon Steels S. A. E. Specification no. Carbon Manganese (minimum and (minimum and Phosphorus (maximum) Sulphur (maximum) Heat treatment maximum) maximum) 1,010 0.05 to 0. 15 0.30 to 0.60 0.045 0.05 Quench at 1,500 1,020 0.15 to 0.25 . 30 to . 60 0.045 0.05 A or B 1,025 0.20 to 0.30 0.50 to 0.80 0.045 0.05 H 1,035 . 30 to . 40 0.50 to 0.80 0.045 0.05 H, D or E 1,045 0.40 to 0.50 0.50 to 0.80 0.045 0.05 H, D or E 1,095 . 90 to 1 . 05 0.25 to 0.50 0.040 0.05 F Table 5. — Screw Stock S. A. E. Specification no. Carbon Manganese Phosphorus (maximum) Sulphur 1,114 0.08 to 0.20 0.30 to 0.80 0.12 0.06 to0.12 Table 6. — NlCKEI j Steels S. A. E. Specifica- tion no. Carbon Manganese Phos- Sul- Nickel (minimum and maximum) (minimum and maximum) phorus (maxi- mum) phur (maxi- mum) (minimum and maximum) Heat treatment 2,315 0.10 to 0.20 0.50 to 0.80 0.04 0.045 3.25 to 3.75 G, H or K 2,320 0.15 to 0.25 0.50 to 0.80 0.04 0.045 3.25 to 3.75 G, H or K 2,330 0.25 to 0.35 0.50 to 0.80 0.04 0.045 3 . 25 to 3 . 75 H or K 2,335 0.30 to 0.40 0.50 to 0.80 0.04 0.045 3 . 25 to 3 . 75 H or K 2,340 0.35 to 0.45 0.50 to 0.80 0.04 0.045 3 . 25 to 3 . 75 H or K 2,345 0.40 to 0.50 0.50 to 0.80 0.04 0.045 3.25 to 3.75 H or K 40 THE WORKING OF STEEL Q tq H WKP o c o X Q Q 6 x x Q Q X X x d o q o o o o © rH rH rH tH o o © tH rH rH o o o -*^ HJ -M o o O o o -r> o o o o O ; O iO iO io io m © OS o o © c. © — o © © © © JO •o PJ 10 PJ IO PI O O O ,-1 rH i-i H H H CO © IO © IO © iO a IO a IO © a a a a © a a iO PJ 10 PJ IO IN iO IO iO t- t~ t- rH rH rH rH rH IN iO l> IN IO PI IO IO iO N.P).tN co co co -S E -5 £ a S 2 co oo oo o o o 10 IO CO © © © co co co © © o 10 PJ. © cc IO co a IO IO PI IO co ■c 10 10 a © © © © © © s © c o o o +S1 o o o +s o IO © iO IN © co IO co IO IO PJ 10 CO IO -f o o o o O iO PJ PI .— I i— 1 © CO IO CO o © ■* PJ rH PJ © © CO Tfl PJ PJ © ■0 Ol co co co co CO CO co co CO 10 10 CO CO © iO CO © Ol co a CO CO © CO CO CO CO CO CO CO X X 'A ALLOYS AND THEIR EFFECT UPON STEEL 41 Table 8. — Chromium Steels S. A. E. Specifica- tion no. Carbon Manganese Phos- Sul- Chromium (minimum and maximum) (minimum and maximum) phorus (maxi- mum) phur (maxi- mum) (minimum and maximum) Heat treatment 5,120 0.15 to 0.25 * 0.04 0.045 0.65 to 0.85 B 5,140 0.35 to 0.45 * 0.04 0.045 . 65 to . 85 H or D 5,165 . 60 to . 70 * 0.04 0.045 . 65 to . S5 H or D 5,195 . 90 to 1 . 05 0.20 to 0.45 0.03 0.03 0.90 to 1.10 M, P or R 51,120 1 . 10 to 1 . 30 0.20 to 0.45 0.03 0.03 . 90 to 1 . 10 M, P or R 5,295 . 90 to 1 . 05 . 20 to . 45 0.03 0.03 1.10 to 1.30 M, P or R 52,120 1 . 10 to 1 . 30 0.20 to 0.45 0.03 0.03 1 . 10 to 1 . 30 M, P or R - Two types of steel are available in this class, one with manganese 0.25 to 0.50 per cent (0.35 per cent desired), and silicon not over 0.20 per cent; the other with manganese 0.60 to 0.S0 per cent (0.70 per cent desired), and silicon 0.15 to 0.50 per cent. Table 9. — Chromium-vanadium Steels S. A. E. Carbon Manganese Phos- Sul- 1 Chromium Vana- Specifica- (minimum (minimum phorus phur (minimum dium treat- and and (maxi- (maxi- and (mini- tion no. ment maximum) maximum) mum) mum) maximum) mum) 6,120 0.15 to0.25 0.50 to 0.80 0.04 0.04 0.80 to 1.10 0.15 S 6,125 0.20 to 0.30 0.50 to 0.80 0.04 0.04 0.80 to 1.10 0.15 S or T 6,130 0.25 to 0.35 0.50 to 0.80 0.04 0.04 0.80 to 1.10 0.15 T or U 6435 0.30 to 0.40 . 50 to . 80 0.04 0.04 0.80 to 1.10 0.15 T or U 6,140 0.35 to 0.45 0.50 to 0.80 0.04 0.04 . 80 to 1 . 10 0.15 T or U 6,145 0.40 to 0.50 0.50 to 0.80 0.04 0.04 0.80 to 1.10 0.15 U 6,150 . 45 to . 55 0.50 to 0.80 0.04 0.04 0.80 to 1.10 0.15 U 6,195 0.90 to 1.05 0.20 to 0.45 0.03 0.03 0.80 to 1.10 0.15 u Table 10.— SlLICO- MANGANESE STEELS S. A. E. Specifica- tion no. Carbon (minimum and maximum) Manganese (minimum and maximum) Phos- phorus (maxi- mum) Sul- phur (maxi- mum) Silicon (minimum and maximum) Heat treat- ment 9,250 9,260 0.45 to 0.55 0.55 to 0.'65 0.60 to 0.80 0.045* 0.50 to 0.70 ! 0.045* 0.045 0.045 1.80 to 2.10 1 . 50 to 1 . 80 V V * Steel made by the acid process may contain maximum 0.05 phosphorus. 42 THE WORKING OF STEEL LIBERTY MOTOR CONNECTING RODS The requirements for materials for the Liberty motor connect- ing rods are so severe that the methods of securing the desired qualities will be of value in other lines. The original specifica- tions called for chrome-nickel but the losses due to the difficulty of handling caused the Lincoln Motor Company to suggest the substitution of chrome-vanadium steel, and thus was accepted by the Signal Corps. The rods were accordingly made from chronium-vanadium steel, containing carbon, 0.30 to 0.40 per cent; manganese, 0.50 to 0.80 per cent; phosphorus, not over 0.04 per cent; sulphur, not over 0.04 per cent; chromium, 0.80 to 1.10 per cent; vanadium, not less than 0.15 per cent. This steel is ordinarily known in the trade as 0.35 carbon steel, S. A. E., specification 6,135, which provides a first rate quality steel for structural parts that are to be heat-treated. The fatigue resist- ing or endurance qualities of this material are excellent. It has a tensile strength of 150,000 lb. minimum per square inch; elastic limit, 115,000 lb. minimum per square inch; elongation, 45 per cent minimum in 2 in.; and minimum reduction in area, 45 per cent. The original production system as outlined for the manu- facturers had called for a heat treatment in the rough-forged state for the connecting rods, and then semi-machining the rod forgings before giving them the final treatment. The Lincoln Motor Company insisted from the first that the proper method would be a complete heat treatment of the forging in the rough state, and machining the rod after the heat treatment. After a number of trial lots, the Signal Corps acceded to the request and production was immediately increased and quality benefited by the change. This method was later included in a revised specification issued to all producers. The original system was one that required a great deal of labor per unit output. The Lincoln organization developed a method of handling connecting rods whereby five workmen ac- complished the same result that would have required about 30 or 32 by the original method. Even after revising the specifica- tion so as to allow complete heat treatments in the rough-forged state, the ordinary methods employed in heat-treating would have required 12 to 15 men. With the fixtures employed, five men could handle 1,300 connecting rods, half of which are plain and half, forked, in a working period of little over 7 hr. ALLOYS AND THEIR EFFECT UPON STEEL 43 t'^ i;- "fm. - • -" mmtHf"- " s;»'^ MIII |!*'S fljBL. A ^fmlm lifli : .. ] Fig. 12. — Rack for holding rods. Fig. 13. — Sliding rods into tank. 44 THE WORKING OF STEEL The increase in production was gained by devising fixtures which enabled fewer men to handle a greater quantity of parts with less effort and in less time. In heat-treating the forgings were laid on a rack or loop A, Fig. 12, made of 1^-in. double extra-heavy pipe, bent up with parallel sides about 9 in. apart, one end being bent straight across and the other end being bent upward so as to afford an easy grasp for the hook. Fifteen rods were laid on each loop, there being four loops of rods charged into a furnace with a hearth area of 36 by 66 in. The rods were charged at a temperature of approximately 900°F. They were heated for refining over a period of 3 hr. to 1,625°F., soaked 15 min, at this degree of heat and quenched in soluble quenching oil. In pulling the heat to quench the rods, the furnace door was raised and the operator pulls one of the loops A, Fig. 13 forward to the shelf of the furnace, supporting the straight end of the loop by means of the porter bar B. They swung the loop of rods around from the furnace shelf and set the straight end of the loop on the edgr of the quenching tank, then raise the curved end C, by means of their hook D so that all the rods on the loop slide into the oil bath. Before the rods cooled entirely, the baskets in the quenching tank were raised and the oil allowed to partly drain off the forg- ings, and they were stacked on curved-end loops or racks and charged into the furnace for the second or hardening heat. The temperature of the furnace was raised in 1}^ hr. to 1,550°F., the rods soaked for 15 min. at this degree of heat and quenched in the same manner as above. They were again drained while yet warm, placed on loops and charged into the furnace for the third or tempering heat. The temperature of the furnace was brought to 1,100°F. in 1 hr., and the rods soaked at this degree of heat for 1 hr. They were then removed from the furnace the same as for quenching, but were dumped onto steel platforms instead of into the quenching oil, and allowed to cool on these steel platforms down to the room temperature. PICKLING THE FORGINGS The forgings were then pickled in a hot solution of either niter cake or sulphuric acid and water at a temperature of 170°F., and using a solution of about 25 per cent. The solution was ALLOYS AND THEIR EFFECT UPON STEEL 45 maintained at a constant point by taking hydrometer readings two or three times a day maintaining a reading of about 1,175. Sixty forked or one hundred single rods were placed in wooden racks and immersed in a lead-lined vat 30 by 30 by 5 ft. long. The rack was lowered or lifted by means of an air hoist and the rods were allowed to stay in solution from y% to 1 hr. depending on the amount of scale. The rods were then swung and lowered in the rack into running vat of running hot water until all trace of the acid was removed. The rod was finally subjected to Brinell test. This shows whether or not the rod has been heat-treated to the proper hardness. If the rods did not read between 241 and 277, they were re-treated until the proper hardness is obtained. CHAPTER IV APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY 1 The success of the Liberty engine program was an engineering- achievement in which the science of metallurgy played an important part. The reasons for the use of certain materials and certain treatments for each part are given with recommen- dations for their application to the problems of automotive industry. The most important items to be taken into consideration in the selection of material for parts of this type are uniformity and machineability. It has been demonstrated many times that the ordinary grades of bessemer screw stock are unsatis- factory for aviation purposes, due to the presence of excessive amounts of unevenly distributed phosphorus and sulphide segregations. For this reason, material finished by the basic open hearth process was selected, in accordance with the following specifications: Carbon, 0.150 to 0.250 per cent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.045 maximum per cent; sulphur, 0.060 to 0.090 per cent. This material in the cold-drawn condition will show: Elastic limit, 50,000; lb. per square inch, elongation in 2 in., 10 per cent reduction of area, 35 per cent. This material gave as uniform physical properties as S. A. E. No. 1020 steel and at the same time was sufficiently free cutting to produce a smooth thread and enable the screw-machine manufacturers to produce, to the same thread limits, approxi- mately 75 per cent as many parts as from bessemer screw stock. There are but seven carbon-steel carbonized parts on the Liberty engine. The most important are the camshaft, the camshaft rocker lever roller and the tappet. The material used for parts of this type was S. A. E. No. 1,020 steel, which is of the following chemical analysis: Carbon 0.150 to 0.250 per cent; manganese, 0.300 to 0.600 per cent; phosphorus, 0.045 maximum per cent; sulphur, 0.050 maximum per cent. 1 Paper presented at the summer meeting of the S. A. E. at Ottawa Beach in June, 1919. 46 APPLICATION OF LIBERTY ENGINE MATERIALS 47 The heat treatment consisted in carbonizing at a temperature of from 1,650 to 1,700°F. for a sufficient length of time to secure the proper depth of case and cool slowly or quench; then reheat to a temperature of 1,380 to 1,430°F. to refine the grain of the case, and quench in water. The only thing that should limit the rate of cooling from the carbonizing heat is distortion. Camshaft rocker lever rollers and tappets, as well as gear pins, were quenched directly from the carbonizing heat in water and then case-refined and rehardened by quenching in water from a temperature of from 1,380 to 1,430°F. The advantage of direct quenching lies in the production of fiber. The rapid cooling causes the strength of the amorphous intercrystalline material to be greater than that of the crystals themselves, which produces the same practical results as are obtained by increasing the amount of amorphous intercrystalline material by refining the grain of the core by a 1,625 to 1,650°F. quench in oil. The existence of this condition causes the shock-resisting properties of the part to be increased greatly. Another advantage obtained from rapid cooling from the carbonizing heat is the retaining of the majority of the excess cementite in solution which produces a less brittle case and by so doing reduces the liability of grinding checks and chipping of the case in actual service. In the case of the camshaft, it is not possible to quench directly from the carbonizing heat because of distortion and therefore excessive breakage during straightening operations. All Liberty camshafts were cooled slowly from carbonizing heat and hardened by a single reheating to a temperature of from 1,380 to 1,430°F. and quenching in water. Considerable trouble has always been experienced in obtaining uniform hardness on finished camshafts. This is caused by insufficient water circulation in the quenching tank, which allows the formation of steam pockets to take place, or by decarbon- ization of the case during heating by the use of an overoxidizing flame. Another cause, which is very often overlooked, is due to the case being ground off one side of cam more than the other and is caused by the roughing master cam.' being slightly different from the finishing master cam. Great care should be taken to see that this condition does not occur, especially when the depth of case is between }^2 and %4 in. 48 THE WORKING OF STEEL CARBON-STEEL FORGINGS Low-stressed carbon-steel forgings include such parts as carbureter control levels, etc. The important criterion for parts of this type is ease of fabrication and freedom from over- heated and burned forgings. The material used for such parts was S. A. E. No. 1,030 steel, which is of the following chemical composition: Carbon, 0.250 to 0.350 percent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.045 maximum per cent; sulphur, 0.050 maximum per cent. To obtain good machineability, all forgings produced from this steel were heated to a temperature of from 1,575 to 1,625°F. to refine the grain of the steel thoroughly and quenched in water and then tempered to obtain proper machineability by heating to a temperature of from 1,000 to 1,100°F. and cooled slowly or quenched. Forgings subjected to this heat treatment are free from hard spots and will show a Brinell hardness of 177 to 217, which is proper for all ordinary machining operations. Great care should be taken not to use steel for parts of this type containing less than 0.25 per cent carbon, because the lower the carbon the greater the liability of hard spots, and the more difficult it becomes to eliminate them. The only satisfactory method so far in commercial use for the elimination of hard spots is to give forgings a very severe quench from a high temperature followed by a proper tempering heat to secure good machineability as outlined above. The important carbon-steel forgings consisted of the cylinders, the propeller-hubs, the propeller-hub flange, etc. The material used for parts of this type was S. A. E. No. 1,045 steel, which is of the following chemical composition : Carbon, 0.400 to 0.500 per cent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.045 maximum per cent; sulphur, 0.050 maximum per cent. All forgings made from this material must show, after heat treatment, the following minimum physical properties: Elastic limit, 70,000; lb. per square inch, elongation in 2 in., 18 per cent, reduction of area, 45; per cent, Brinell hardness, 217 to 255. To obtain these physical properties, the forgings were quenched in water from a temperature of 1,500 to 1,550°F., followed by tempering to meet proper Brinell requirements by heating to a temperature of 1,150 to 1,200°F. and cooled slowly or APPLICATION OF LIBERTY ENGINE MATERIALS 49 quenched. No trouble of any kind was ever experienced with parts of this type. The principal carbon-steel pressed parts used on the Liberty engine were the water jackets and the exhaust manifolds. The material used for parts of this type was S. A. E. No. 1,010 steel, which is of the following chemical composition: Carbon, 0.050 to 0.150 per cent; manganese, 0.300 to 0.600 per cent; phosphorus, 0.045 maximum per cent; sulphur, 0.045 maximum per cent. No trouble was experienced in the production of any parts from this material with the exception of the water jacket. Due to the particular design of the Liberty cylinder assembly, many failures occurred in the early days, due to the top of the jacket cracking from fatigue. It was found that these fatigue failures were caused primarily from the use of jackets which showed small scratches or die marks at this joint and secondarily bj' improper annealing of the jackets themselves between the different forming operations. By a careful inspection for die marks and by giving the jackets 1,400°F. annealing before the last forming operation, it was possible to completely eliminate the trouble encountered. HIGHLY STRESSED PARTS The highly stressed parts on the Libert}' engine consisted of the connecting-rod bolt, the main-bearing bolt, the propeller- hub key, etc. The material used for parts of this type was selected at the option of the manufacturer from standard S. A. E. steels, the composition of which are given in Table 11. Table 11.— Composition of S. A. E. Steels Nos. 2,330, 3,135 and 6,130 Steel No 2,330 3,135 6,130 Carbon, minimum 0.250 0.300 0.250 Carbon, maximum . 350 . 400 . 450 Manganese, minimum 0.500 0.500 0.500 Manganese, maximum . 800 . 800 . 800 Phosphorus, maximum 0.045 0.040 0.040 Sulphur, maximum . 045 . 045 0. 045 Nickel, minimum 3 . 250 1 . 000 Nickel, maximum 3 . 750 1 . 500 Chromium, minimum . 450 . 800 Chromium, maximum . 750 1 . 100 Vanadium, minimum 0. 150 4 50 THE WORKING OF STEEL All highly stressed parts on the Liberty engine must show, after heat treatment, the following minimum physical properties : Elastic limit, 100,000; lbs. per square inch, elongation in 2 in., 16 per cent; reduction of area, 45 per cent; scleroscope hardness, 40 to 50. The heat treatment employed to obtain these physical proper- ties consisted in quenching from a temperature of 1,525 to 1,575°F., in oil, followed by tempering at a temperature of from 925 to 975°F. Due to the extremely fine limits used on all threaded parts for the Liberty engine, a large percentage of rejection was due to warpage and scaling of parts. To eliminate this objection, many of the Liberty engine builders adopted the use of heat- treated and cold-drawn alloy steel for their highly stressed parts. On all sizes up to and including % in. in diameter, the physical properties were secured by merely normalizing the hot-rolled bars by heating to a temperature of from 1,525 to 1,575°F., and cooling in air, followed by the usual cold-drawing reductions. For parts requiring stock over % in. in diameter, the physical properties desired were obtained by quenching and tempering the hot-rolled bars before cold-drawing. It is the opinion that the use of heat-treated and. cold-drawn bars is very good practice, provided proper inspection is made to guarantee the uniformity of heat treatment and, therefore, the uniformity of the physical properties of the finished parts. The question has been asked many times by different manu- facturers, as to which alloy steel offers the best machineability when heat-treated to a given Brinell hardness. The general consensus of opinion among the screw-machine manufacturers is that S. A. E. No. 6,130 steel gives the best machineability and that S. A. E. No. 2,330 steel would receive second choice of the three specified. In the finishing of highly stressed parts for aviation engines, extreme care must be taken to see that all tool marks are elimi- nated, unless they are parallel to the axis of strain, and that proper radii are maintained at all changes of section. This is of the utmost importance to give proper fatigue resistance to the part in question. GEARS The material used^for all gears on the Liberty engine was selected at the option of the manufacturer from the following APPLICATION OF LIBERTY ENGINE MATERIALS 51 standard S. A. E. steels, the composition of which are given in Table 12. Table 12.- — Composition of Steels Nos. X-3,340 and 6,140 Steel No X-3,340 6,140 Carbon, minimum 0.350 0.350 Carbon, maximum 0.450 0.450 Manganese, minimum 0.450 0.500 Manganese, maximum . 750 . 800 Phosphorus, maximum . 040 . 040 Sulphur, maximum 0.045 0.045 Nickel, minimum 2 . 750 Nickel, maximum 3 . 250 Phosphorus, maximum . 700 . 800 Phosphorus, maximum . 950 1 . 100 Vanadium, minimum 0. 150 All gears were heat-treated to a scleroscope hardness of from 55 to 65. The heat treatment used to secure this hardness consisted in quenching the forgings from a temperature of 1,550 to 1,600°F. in oil and annealing for good machineability at a temperature of from 1,300 to 1,350°F. Forgings treated in this manner showed a Brinell hardness of from 177 to 217. RATE OF COOLING At the option of the manufacturer, the above treatment of gear forgings could be substituted by normalizing the forgings at a temperature of from 1,550 to 1,600°F. The most important criterion for proper normalizing consisted in allowing the forgings to cool through the critical temperature of the steel, at a rate not to exceed 50°F. per hour. For the two standard steels used, this consisted in cooling from the normalizing temperature down to a temperature of 1,100°F., at the rate indicated. Forg- ings normalized in this manner will show a Brinell hardness of from 177 to 217. The question has been repeatedly asked as to which treatment will produce the higher quality finished part. In answer to this i will state that on simple forgings of com- paratively small section, the normalizing treatment will produce a finished part which is of equal quality to that of the quenched and annealed forgings. However, in the case of complex forg- ings, or those of large section, more uniform physical properties of the finished part will be obtained by quenching and annealing the forgings in the place of normalizing. 52 THE WORKING OF STEEL The heat treatment of the finished gears consisted of quenching in oil from a temperature of from 1,420 to 1,440°F. for the No. X-3,340 steel, or from a temperature of from 1,500 to 1,540°F. for No. 6,140 steel, followed by tempering in saltpeter or in an electric furnace at a temperature of from 650 to 700°F. The question has been asked by many engineers, why is the comparatively low scleroscope hardness specified for gears? The reason for this is that at best the life of an aviation engine is short, as compared with that of an automobile, truck or tractor, and that shock resistance is of vital importance. A sclerescope hardness of from 55 to 65 will give sufficient resistance to wear to prevent replacements during the life of an aviation engine, while at the same time this hardness produces approxi- mately 50 per cent greater shock-resisting properties to the gear. In the case of the automobile, truck or tractor, resistance to wear is the main criterion and for that reason the higher hardness is specified. Great care should be taken in the design of an aviation engine gear to eliminate sharp corners at the bottom of teeth as well as in keyways. Any change of section in any stressed part of an aviation engine must have a radius of at least 3^2 in- to give proper shock and fatigue resistance. This fact has been demonstrated many times during the Liberty engine program. CONNECTING RODS The material used for all connecting rods on the Liberty engine was selected at the option of the manufacturer from one of two standard S. A. E. steels, the composition of which are given in Table 13. Table 13. — Composition of Steels Nos. X-3,335 and 6,135 Steel No X-3,335 6,135 Carbon, minimum 0.300 0.300 Carbon, maximum 0.400 0.400 Manganese, minimum 0.450 0.500 Manganese, maximum . 750 . 800 Phosphorus, maximum 0.040 0.040 Sulphur, maximum . 045 . 045 Nickel, minimum 2 . 750 Nickel, maximum 3 . 250 Chromium, minimum 0. 700 0. 800 Chromium, maximum 0. 950 1 . 100 Vanadium, minimum. 0. 150 APPLICATION OF LIBERTY ENGINE MATERIALS 53 All connecting rods were heat-treated to show the following minimum physical properties; Elastic limit, 105,000 lb. per square inch: elongation in 2 in., 17.5; per cent, reduction of area 50.0; per cent., Brinell hardness, 241 to 277. The heat treatment used to secure these physical properties consisted in normalizing the forgings at a temperature of from 1,550 to 1,600°F., followed by cooling in the furnace or in air. The forgings were then quenched in oil from a temperature of from 1,420 to 1,440°F. for the No. X-3,335 steel, or from a tem- perature of from 1,500 to 1,525°F. for No. 6,135 steel, followed by tempering at a temperature of from 1,075 to 1,150°F. At the option of the manufacturer, the normalizing treatment could be substituted by quenching the forgings from a temperature of from 1,550 to 1,600°F., in oil, and annealing for the best machine- ability at a temperature of from 1,300 to 1,350°F. The double quench, however, did not prove satisfactory on No. X-3,335 steel, due to the fact that it was necessary to remove forgings from the quenching bath while still at a temperature of from 300 to 500 °F. to eliminate any possibility of cracking. In view of the fact that this practice is difficult to carry out in the average heat-treating plant, considerable trouble was experienced. The most important criterion in the production of aviation engine connecting rods is the elimination of burned or severely overheated forgings. Due to the particular design of the forked rod, considerable trouble was experienced in this respect because of the necessitjr of reheating the forgings before they are com- pletely forged. As a means of elimination of burned forgings, test lugs were forged on the channel section as well as on the top end of fork. After the finish heat treatment, these test lugs were nicked and broken and the fracture of the steel carefully ex- amined. This precaution made it possible to eliminate burned forgings as the test lugs were placed on sections which would be most likely to become burned. There is a great difference of opinion among engineers as to what physical properties an aviation engine connecting rod should have. Many of the most prominent engineers contend that a connecting rod should be as stiff as possible. To produce rods in this manner in any quantity, it is necessary for the final heat treatment to be made on the semi-machined rod. This practice would make it necessary for a larger percentage of the semi- machined rods to be cold-straightened after the finish heat 54 THE WORKING OF STEEL treatment. The cold-straightening operation on a part having important functions to perform as a connecting rod is extremely dangerous. In view of the fact that a connecting rod functions as a strut, it is considered that this part should be only stiff enough to prevent any whipping action during the running of the engine. The greater the fatigue-resisting property that one can put into the rod after this stiffness is reached, the longer the life of the rod will be. This is the reason for the Brinell limits mentioned being specified. In connection with the connecting rod, emphasis must be laid on the importance of proper radii at all changes of section. The connecting rods for the first few Liberty engines were machined with sharp corners at the point where the connecting- rod bolt-head fits on assembly. On the first long endurance test of a Liberty engine equipped with rods of this type, failure resulted from fatigue starting at this point. It is interesting to note that every rod on the engine which did not completely fail at this point had started to crack. The adoption of a ;H$2-in. radius at this point completely eliminated fatigue failures on Liberty rods. CRANKSHAFT The crankshaft was the most highly stressed part of the entire Liberty engine, and, therefore, every metallurgical pre- caution was taken to guarantee the quality of this part. The material used for the greater portion of the Liberty crankshafts produced was nickel-chromium steel of the following chemical composition: Carbon, 0.350 to 0.450 per cent; manganese, 0.300 to 0.600 per cent; phosphorus, 0.040 maximum per cent; sulphur, 0.045 maximum per cent; nickel, 1.750 to 2.250 per cent; chromium, 0.700 to 0.900 per cent. Each crankshaft was heat-treated to show the following minimum physical properties: Elastic limit, 116,000 lb. per square inch; elongation in 2 in., 16 per cent, reduction of area, 50 per cent, Izod impact, 34 ft. -lb.; Brinell hardness, 266 to 321. For every increase of 4,000 lb. per square inch in the elastic limit above 116,000 lb. per square inch, the minimum Izod impact required was reduced 1 ft.-lb. The heat treatment used to produce these physical properties consisted in normalizing the forgings at a temperature of from 1,550 to 1,600°F., followed by quenching in water at a temper- APPLICATION OF LIBERTY ENGINE MATERIALS 55 ature of from 1,475 to 1,525°F. and tempering at a temperature of from 1,000 to 1,100°F. It is absolutely necessary that the crankshafts be removed from the quenching tank before being- allowed to cool below a temperature of 500°F., and immediately placed in the tempering furnace to eliminate the possibility of quenching cracks. A prolongation of not less than the diameter of the forging bearing was forged on one end of each crankshaft. This was removed from the shaft after the finish heat treatment, and physical tests were made on test specimens which were cut from it at a point half way between the center and the surface. One tensile test and one impact test were made on each crank- shaft, and the results obtained were recorded against the serial number of the shaft in question. This serial number was carried through all machining operations and stamped on the cheek of the finished shaft. In addition to the above tensile and impact tests, at least two Brinell hardness determinations were made on each shaft. All straightening operations on the Liberty crankshaft which were performed below a temperature of 500°F. were followed by retempering at a temperature of approximately 200°F. below the original tempering temperature. Another illustration of the importance of proper radii at all changes of section is given in the case of the Liberty crankshaft. The presence of tool marks or under cuts must be completely eliminated from an aviation engine crankshaft to secure proper service. During the duration of the Liberty program, four crankshafts failed from fatigue, failures starting from sharp corners at bottom of propeller-hub keyway. Two of the shafts that failed showed torsional spirals running more than completely around the shaft. As soon as this difficulty was removed no further trouble was experienced. One of the most important difficulties encountered in connec- tion with the production of Liberty crankshafts was hair-line seams. The question of hair-line seams has been discussed to greater length by engineers and metallurgists during the war than any other single question. Hair-line seams are caused by small non-metallic inclusions in the steel. There is every reason to believe that these inclusions are in the greater majority of cases manganese sulphide. There is a great difference of opinion as to the exact effect of hair-line seams on the service of an aviation 56 THE WORKING OF STEEL engine crankshaft. It is the opinion of many that hair-line seams do not in any way affect the endurance of a crankshaft in service, provided they are parallel to the grain of the steel and do not occur on a fillet. Of the 20,000 Liberty engines produced, fully 50 per cent of the crankshafts used contain hair-line seams but not at the locations mentioned. There has never been a failure of a Liberty crankshaft which could in any way be traced to hair-line seams. It was found that hair-line seams occur generally on high nickel-chromium steels. One of the main reasons why the com- paratively mild analysis nickel-chromium steel was used was due to the very few hair-line seams present in it. It was also deter- mined that the hair lines will in general be found near the surface of the forgings. For that reason, as much finish as possible was allowed for machining. A number of tests have been made on forging bars to determine the depths at which hair-line seams are found, and many cases came up in which hair-line seams were found % in. from the surface of the bar. This means that in case a crankshaft does not show hair-line seams on the ground surface this is no indication that it is free from such a defect. One important peculiarity of nickel-chromium steel was brought out from the results obtained on impact tests. This peculiarity is known as "blue brittleness. " Just what the effect of this is on the service of a finished part depends entirely upon the design of the particular part in question. There have been no failures of any nickel-chromium steel parts in the automotive industry which could in any way be traced to this phenomena. Whether or not nickel-chromium-steel forgings will show "blue brittleness" depends entirely upon the temperature at which they are tempered and their rate of cooling from this temperature. The danger range for tempering nickel-chromium steels is be- tween a temperature of from 400 to 1,100°F. From the data so far gathered on this phenomena, it is necessary that the nickel- chromium steel to show "blue brittleness" be made by the acid process. There has never come to my attention a single instance in which basic open hearth steel has shown this phenomena. Just why the acid open hearth steel should be sensitive to "blue brittleness" is not known. All that is necessary to eliminate the presence of "blue brittle- ness" is to quench all nickel-chromium-steel forgings in water from their tempering temperature. The last 20,000 Liberty crankshafts that were made were quenched in this manner. APPLICATION OF LIBERTY ENGINE MATERIALS 57 PISTON PIN The piston pin on an aviation engine must possess maximum resistance to wear and to fatigue. For this reason, the piston pin is considered, from a metallurgical standpoint, the most important part on the engine to produce in quantities and still possess the above characteristics. The material used for the Liberty engine piston pin was S. A. E. No. 2315 steel, which is of the following chemical composition: Carbon, 0.100 to 0.200 per cent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.040 maximum per cent; sulphur, 0.045 maximum per cent; nickel, 3.250 to 3.750 per cent. Each finished piston pin, after heat treatment, must show a minimum scleroscope hardness of the case of 70, a scleroscope hardness of the core of from 35 to 55 and a minimum crushing strength when supported as a beam and the load applied at the center of 35,000 lb. The heat treatment used to obtain the above physical properties consisted in carburizing at a temperature not to exceed 1,675°F., for a sufficient length of time to secure a case of from 0.02 to 0.04 in. deep. The pins are then allowed to cool slowly from the carbonizing heat, after which the hole is finish- machined and the pin cut to length. The finish heat treatment of the piston pin consisted in quenching in oil from a temperature of from 1,525 to 1,575°F. to refine the grain of core properly and then quenching in oil at a temperature of from 1,340 to 1,380°F. to refine and harden the grain of the case properly, as well as to secure proper hardness of core. After this quenching, all piston pins are tempered in oil at a temperature of from 375 to 400 °F. A 100 per cent inspection for scleroscope hardness of the case and the core was made, and no failures were ever recorded when the above material and heat treatment was used. APPLICATION TO THE AUTOMOTIVE INDUSTRY The information given on the various parts of the Liberty engine applies with equal force to the corresponding parts in the construction of an automobile, truck or tractor. We recommend as first choice for carbon-steel screw-machine parts material produced by the basic open hearth process and having the follow- ing chemical composition; Carbon, 0.150 to 0.250 per cent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.045 maxi- mum per cent; sulphur, 0.075 to 0.150 per cent. 58 THE WORKING OF STEEL This material is very uniform and is nearly as free cutting as bessemer screw stock. It is sufficiently uniform to be used for unimportant carburized parts, as well as for non-heat-treated screw-machine parts. A number of the large automobile manu- facturers are now specifying this material in preference to the regular bessemer grades. As second choice for carbon-steel screw-machine parts we recom- mend ordinary bessemer screw stock, purchased in accordance with S. A. E. specification No. 1114. The advantage of using No. 1114 steel lies in the fact that the majority of warehouses carry standard sizes of this material in stock at all times. The disad- vantage of using this material is due to its lack of uniformity. The important criterion for transmission gears is resistance to wear. To secure proper resistance to wear a Brinell hardness of from 512 to 560 must be obtained. The material selected to obtain this hardness should be one which can be made most nearly uniform, will undergo forging operations the easiest, will be the hardest to overheat or burn, will machine best and will respond to a good commercial range of heat treatment. It is a well-known fact that the element chromium, when in the form of chromium carbide in alloy steel, offers the greatest resistance to wear of any combination yet developed. It is also a well-known fact that the element nickel in steel gives excellent shock-resisting properties as well as resistance to wear but not nearly as great a resistance to wear as chromium. It has been standard practice for a number of years for many manufacturers to use a high nickel-chromium steel for transmission gears. A typical nickel-chromium gear specification is as follows : Carbon, 0.470 to 0.520 per cent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.040 maximum per cent; sulphur, 0.045 maximum per cent; chromium, 0.700 to 0.950 per cent- There is no question but that a gear made from material of such an analysis will give excellent service. However, it is possi- ble to obtain the same quality of service and at the same time appreciably reduce the cost of the finished part. The gear steel specified is of the air-hardening type. It is extremely sensitive to secondary pipe, as well as seams, and is extremely diffiuclt to forge and very easy to overheat. The heat-treatment range is very wide, but the danger from quenching cracks is very great. In regard to the machineability, this material is the hardest to machine of any alloy steel known. APPLICATION OF LIBERTY ENGINE MATERIALS 59 COMPOSITION OF TRANSMISSION-GEAR STEEL If the nickel content of this steel is eliminated, and the per- centage of chromium raised slightly, an ideal transmission-gear material is obtained. This would, therefore, be of the following composition: Carbon, 0.470 to 0.520 per cent; manganese, 0.500 to 0.800 per cent; phosphorus, 0.040 maximum per cent; sulphur, 0.045 maximum per cent; chromium, 0.800 to 1.100 per cent. The important criterion in connection with the use of this material is that the steel be properly deoxidized, either through the use of ferrovanadium or its equivalent. Approximately 2,500 sets of transmission gears are being made daily from material of this analysis and are giving entirely satisfactory results in service. The heat treatment of the above material for trans- mission gears is as follows: "Normalize forgings at a temperature of from 1,550 to 1,600°F. Cool from this temperature to a tem- perature of 1,100°F. at the rate of 50° per hour. Cool from 1,100°F., either in air or quench in water." Forgings so treated will show a Brinell hardness of from 177 to 217, which is the proper range for the best machineability. The heat treatment of the finished gears consists of quenching in oil from a temperature of 1,500 to 1,540°F., followed by tempering in oil at a temperature of from 375 to 425°F. Gears so treated will show a Brinell hardness of from 512 to 560, or a scleroscope hardness of from 72 to 80. One tractor builder has placed in service 20,000 sets of gears of this type of material and has never had to replace a gear. Taking into consideration the fact that a tractor transmission is subjected to the worst possible service conditions, and that it is under high stress 90 per cent of the time, it seems inconceivable that any appreciable transmission trouble would be experienced when material of this type is used on an automobile, where the full load is applied not over 1 per cent of the time, or on trucks where the full load is applied not over 50 per cent of the time. The gear hardness specified is necessary to reduce to a mini- mum the pitting or surface fatigue of the teeth. If gears having a Brinell hardness of over 560 are used, danger is encountered, due to low shock-resisting properties. If the Brinell hardness is under 512, trouble is experienced due to wear and surface fatigue of the teeth. For ring gears and pinions material of the following chemical composition is recommended: Carbon, 0.100 to 0.200 per cent; 60 THE WORKING OF STEEL manganese, 0.350 to 0.650 per cent; phosphorus, 0.040 maximum per cent; sulphur, 0.045 maximum per cent; chromium, 0.550 to 0.750 per cent; nickel, 0.400 to 0.600 per cent. Care should be taken to see that this material is properly deoxidized either by the use of ferro vanadium or its equivalent. The advantage of using a material of the above type lies in the fact that it will produce a satisfactory finished part with a very simple treatment. The heat treatment of ring gears and pinions is as follows: "Carburize at a temperature of from 1,650 to 1,700°F. for a sufficient length of time to secure a depth of case of from \^2 to % 4 in., and quench directly from carburizing heat in oil. Reheat to a temperature of from 1,430 to 1,460°F. and quench in oil. Temper in oil at a temperature of from 375 to 425°F. The final quenching operation on a ring gear should be made on a fixture similar to the Gleason press to reduce distortion to a minimum." One of the largest producers of ring gears and pinions in the automotive industry has been using this material and treatment for the last 2 years, and is of the opinion that he is now producing the highest quality product ever turned out by that plant. On some designs of automobiles a large amount of trouble is experienced with the driving pinion. If the material and heat treatment specified will not give satisfaction, rather than to change the design it is possible to use the following analysis material, which will raise the cost of the finished part but will give excellent service: Carbon, 0.100 to 0.200 per cent; manga- nese, 0.350 to 0.650 per cent; phosphorus, 0.040 maximum per cent; sulphur, 0.045 maximum per cent; nickel, 4.750 to 5.250 per cent. The heat treatment of pinions produced from this material consists in carburizing at a temperature of from 1,600 to 1,650°F. for a sufficient length of -time to secure a depth of case from 3^2 to %4 in. The pinions are then quenched in oil from a tempera- ture of 1,500 to 1,525°F. to refine the grain of the core and quenched in oil from a temperature of from 1,340 to 1,360°F. to refine and harden the case. The use of this material however, is recommended only in an emergency, as high-nickel steel is very susceptible to seams, secondary pipe and laminations. The main criterion on rear-axle and pinion shafts, steering knuckles and arms and parts of this general type is resistance to fatigue and torsion. The material recommended for parts of APPLICATION OF LIBERTY ENGINE MATERIALS 61 this character is either S. A. E. No. 6135 or No. 3135 steel, which have the chemical composition given in Tables 9 and 7. HEAT TREATMENT OF AXLES Parts of this general type should be heat-treated to show the following minimum physical properties: Elastic limit, 115,000 lb. per square inch; elongation in 2 in., 16 per cent; reduction of area, 50 per cent; Brinell hardness, 277 to 321. The heat treatment used to secure these physical properties consists in quenching from a temperature of from 1,520 to 1,540°F. in water and tempering at a temperature of from 975 to 1,025°F. Where the axle shaft is a forging, and in the case of steering- knuckles and arms, this heat treatment should be preceded by normalizing the forgings at a temperature of from 1,550 to 1,600°F. It will be noted that these physical properties correspond to those worked out for an ideal aviation engine crankshaft. If parts of this type are designed with proper sections, so that this range of physical properties can be used, the part in question will give maximum service. One of the most important developments during the Liberty engine program was the fact that it is not necessary to use a high- analysis alloy steel to secure a finished part which will give proper service. This fact should save the automotive industry millions of dollars on future production. If the proper authority be given the metallurgical engineer to govern the handling of the steel from the time it is purchased until it is assembled into finished product, mild-analysis steels can be used and the quality of the finished product guaranteed. It was only through the careful adherence to these fundamental principles that it was possible to produce 20,000 Liberty engines, which are considered to be the most highly stressed mechanism ever produced, without the failure of a single engine from defec- tive material or heat treatment. MAKING STEEL BALLS Steel balls are made from rods or coils according to size, stock less than %6 -m - comes in coils. Stock %-in. and larger curves in rods. Ball stock is designated in thousandths so that %-in. rods are known as 0.625-in. stock. 62 THE WORKING OF STEEL Steel for making balls of average size is made up of : Carbon 0. 95 to 1 . 05 per cent Silicon 0.20 to 0.35 per cent Manganese 0.30 to 0.45 per cent Chromium 0.35 to 0.45 per cent Sulphur and phosphorus not to exceed ... . 025 per cent For the larger sizes a typical analysis is : Carbon 1 . 02 per cent Silicon 0. 21 per cent Manganese . 40 per cent Chromium 0. 65 per cent Sulphur : . . . . 026 per cent Phosphorus : . 014 per cent Balls % in. and below are formed cold on upsetting or heading machines, the stock use is as follows: Table 14 — Sizes of Stock for Forming Balls on Header Diameter of Diameter of Diameter of Diameter of ball, inch stock inch ball, inch stock, inch H 0.100 He 0.235 %2 0.120 % 0.275 Vie 0.145 He 0.320 V32 0.170 y% 0.365 K 0.190 Vie 0.395 %2 0.220 % 0.440 For larger balls the blanks are hot-forged from straight bars. They are usually forged in multiples of four under a spring hammer and then separated by a suitable punching or shearing die in a press adjoining the hammer. The dimensions are: Diameter of ball, inch Diameter of die, inch Diameter of stock, inch H % l 0.775 0.905 1.035 0.625 0.729 0.823 APPLICATION OF LIBERTY ENGINE MATERIALS 63 Before hardening, the balls are annealed to relieve the stresses of forging and grinding, this being done by passing them through a revolving retort made of nichrome or other heat-resisting sub- stance. The annealing temperature is 1,300°F. The hardening temperature is from 1,425 to 1,475°F. according to size and composition of steel. Small balls, %q and under, are quenched in oil, the larger sizes in water. In some special cases brine is used. Quenching small balls in water is too great a shock as the small volume is cooled clear through almost instantly. The larger balls have metal enough to cool more slowly. Balls which are cooled in either water, or brine are boiled in water for 2 hr. to relieve internal stresses, after which the balls are finished by dry-grinding and oil-grinding. The ball makers have an interesting method of testing stock for seams which do not show in the rod or wire. The Hoover Steel Ball Company cut off pieces of rod or wire %6 m - l° n g and subject them to an end pressure of from 20,000 to 50,000 lb. A pressure of 20,000 lb. compresses the piece to % q in. and the 50,000 lb. pressure to %2 in. This opens any seam which may exist but a solid bar shows no seam. Another method which has proved very successful is to pass the bar or rod to be tested through a solenoid electro-magnet. With suitable instruments it is claimed that this is an almost infallible test as the instruments show at once when a seam or flaw is present in the bar. CHAPTER V THE FORGING OF STEEL So much depends upon the forging of steel that it must be carefully considered. The main points are the heating to the proper temperature and the use of a hammer of the right size for the work to be forged. The bar of stock from which a forging was made may have had a fairly good structure, but if the shock of the falling die struck this bar of stock when at a temperature lower than the critical, its structure would become distorted, some of the crystals broken down and others reformed. If the temperature of the bar, however, was above the critical point, and the steel in an austenitic condition when the die struck it, the resulting steel will be a fairly uniform formation of aus- tenite crystals. Although the original structure will have been changed, the forged piece will still have the characteristic aus- tenite. Thus it is seen that the steel must be worked at the proper temperature. Steel Worked in Austenitic Stage. — As a general rule steel should be worked when it is in the austenitic stage. It is then sure to keep a uniform structure because the carbon is in solid solution with the iron and is therefore distributed uniformly throughout the metal. If it is worked below the critical point, the carbon has begun to stratify and form different combinations and carbides with the result that uniformity is not apt to result. Just as soon as the temperature begins to fall below the critical point the austenite begins to break up into ferrite and cementite. If the carbon content of the steel is high, cementite will result, and if it is low the greater part will be composed of ferrite. By working the steel well above the critical temperature the size of the austenite crystals is kept small and although on cooling the austenite crystals will not remain in that form if they are finely divided, the size of the grains of the final result will be much smaller and hence a more uniform structure will result. A final steel will be composed of pearlite; ferrite and pearlite; or cementite and pearlite, according to the carbon content. The higher the carbon content the greater percentage of cementite, 64 THE FORGING OF STEEL 65 and therefore the harder the steel. It can always be remembered that the cause of the great effect of carbon on steel is due to the fact that it only takes 1 per cent of carbon to form 15 per cent of cementite — the hard, brittle constituent of the high-carbon steel. The ultimate object is to secure a fine, uniform grain and this can be secured by not reheating the metal to too high a tempera- ture and by thoroughly rolling it or working it at a temperature well above its critical point. If this is correctly done the micro- photograph will show a fine, evenly distributed grain which, in the case of carbon steel, will be composed of ferrite and pearlite. The ferrite is light gray and the pearlite has a black, stratified appearance on the microphotograph; the percentage of carbon will determine the relative quantities of ferrite and pearlite, i.e., the lower the carbon, the more ferrite. Steel Can be Worked Cold. — Steel can be worked cold, as in the case of cold-rolled steel, but afterwards it must be annealed in order to remove the internal strains which have resulted from the cold working. The annealing must be done above the critical point, i.e., at which the steel has been again raised to the austen- itic condition where the iron carbide is in solution, and on cooling a complete re-crystallization results. In annealing steel care must be taken that the exterior surface does not become oxidized, owing to the tendency of the metal to absorb oxygen while hot. When the surface becomes oxidized scale forms which peels off under slight stresses. FORGING High-speed Steel. — Heat very slowly and carefully to from 1,800 to 2,000°F. and forge thoroughly and uniformly. If the forging operation is prolonged do not continue forging the tool when the steel begins to stiffen under the hammer. Do not forge below 1,700°F. (a dark lemon or orange color). Reheat frequently rather than prolong the hammering at the low heats. After finishing the forging allow the tool to cool as slowly as possible in lime or dry ashes; avoid placing the tool on the damp ground or in a draught of air. Use a good clean fire for heating. Do not allow the tool to soak at the forging heat. Do not heat any more of the tool than is necessary in order to forge it to the desired shape. Carbon Tool Steel. — Heat to a bright red, about 1,500 to 1,550°F. Do not hammer steel when it cools down to a dark 5 66 THE WORKING OF STEEL cherry red, or just below its hardening point, as this creates surface cracks. Oil -hardening Steel. — Heat slowly and uniformly to 1,450°F. and forge thoroughly. Do not under any circumstances at- tempt to harden at the forging heat. After cooling from forging reheat to about 1,450°F. and cool slowly so as to remove forging strains. Chrome -nickel Steel. — Forging heat of chrome-nickel steel depends very largely on the percentage of each element con- tained in the steel. Steel containing from 3^ to 1 per cent chrome and from 1^ to 3^ per cent nickel, with a carbon content equal to the chromium, should be heated very slowly and uniformly to approximately 1,600°F., or salmon color. After forging, reheat the steel to about 1,450° and cool slowly so as to remove forging strains. Do not attempt to harden the steel before such annealing. A great deal of steel is constantly being spoiled by carelessness in the forging operation. The billets may be perfectly sound, but even if the steel is heated to a good forging heat, and is hammered after the outside surface becomes cold, a poor forging results. For, while the center of steel remained at the forging heat, hammering simply cooled the steel away from the center, opening the steel and making a bad pipe. Steel which is heated quickly and forging begun before uni- form heat has penetrated to its center is shocked by hammer blows. This opens up seams because the cooler central portion was not able to flow with the hot metal surrounding it. Uni- form heating is absolutely necessary for the best results. Figure 14 shows a sound forging. The bars in Fig. 15 were burst by improper forging, while the die, Fig. 16, burst from a piped center. Figure 17 shows a piece forged with a hammer too light for the size of the work. This gives an appearance similar to case- hardening, the refining effect of the blows reaching but a short distance from the surface. The size of hammers for forgings is important and the following- data from the "American Machinists Handbook" is of value as a general guide. While it is impossible to accurately rate the capacity of steam hammers with respect to the size of work they should handle, on account of the greatly varying conditions, a few notes from the THE FORGING OF STEEL 67 experience of the Bement works of the Niles-Bement-Pond Company will be of service. For making an occasional forging of a given size, a smaller hammer may be used than if we are manufacturing this same Fig. 14. — A sound forging. Fig. 15. — Burst from improper forging. piece in large quantities. If we have a 6-in. piece to forge, such as a pinion or a short shaft, a hammer of about 1,100-lb. capacity would answer very nicely. But should the general work be as 68 THE WORKING OF STEEL large as this, it would be very much better to use a 1,500-lb. hammer. If, on the other hand, we wish to forge 6-in. axles economically, it would be necessary to use a 7,000- or 8,000-lb. hammer. The following table will be found convenient for Fig. 16. — Burst from a piped center. Fig. 17. — Result of using too light a hammer. reference for the proper size of hammer to be used on different classes of general blacksmith work, although it will be understood that it is necessary to modify these to suit conditions, as has already been indicated. THE FORGING OF STEEL 69 Diameter of stock Size of hammer Sy 2 in 250 to 350 1b. 4 in 350 to 600 1b. AY 2 in 600 to 800 1b. 5 in 800 to 1,000 lb. 6 in . 1,100 to 1,500 1b. Steam hammers are always rated by the weight of the ram, and the attached parts, which include the piston and rod, nothing being added on account of the steam pressure behind the piston. This makes it a little difficult to compare them with plain drop or tilting hammers, which are also rated in the same way. ABC Fig. 18. — Good and bad forgings. Steam hammers are usually operated at pressures varying from 75 to 100 lb. of steam per square inch, and may also be operated by compressed air at about the same pressures. It is cheaper, however, in the case of compressed air to use pressures from 60 to 80 lb. instead of going higher. Forgings must, however, be made from sound billets if satis- factory results are to be secured. Figure 18 shows three cross- sections of which A is sound, B is badly piped and C is worthless. PLANT FOR FORGING RIFLE BARRELS The forging of rifle barrels in large quantities and heat-treating them to meet the specifications demanded by some of the foreign governments led Wheelock, Lovejoy & Company to establish a complete plant for this purpose in connection with their ware- house in Cambridge, Mass. This plant, designed and constructed 70 THE WORKING OF STEEL THE FORGING OF STEEL 71 by their chief engineer, K. A. Juthe, had many interesting fea- tures. Many features of this plant can be modified for other classes of work. The stock, which came in bars of mill length, was cut off so as to make a barrel with the proper allowances for trimming (Fig. 19). They then pass to the forging or upsetting press in the adjoining room. This press, which is shown in more detail in Fig. 20 handled the barrels from all the heating furnaces shown. The men changed work at frequent intervals, to avoid excessive fatigue. iting furnace. Then the barrels were reheated in the continuous furnace, shown in Fig. 21, and straightened before being tested. The barrels were next tested for straightness. After the heat- treating, the ends are ground, a spot ground on the enlarged end and each barrel tested on a Brinell machine. The pressure used is 3,000 kg., or 6,614 lb., and a depression of 3.9 mm., or No. 241, is usually secured. The heat-treating of the rifle blanks covered four separate operations: (1) Heating and soaking the steel above the critical temperature and quenching in oil to harden the steel through to the center; (2) reheating for drawing of temper for the purpose 72 THE WORKING OF STEEL of meeting the physical specifications; (3) reheating to meet the machineability test for production purposes; and (4) reheating to straighten the blanks while hot. A short explanation of the necessity for the many heats may be interesting. For the first heat, the blanks were slowly brought to the required heat, which is about 150°F. above the critical temperature. They are then soaked at a high heat for about 1 hr. before quenching. The purpose of this treatment is to eliminate any rolling or heat stresses that might be in the bars from mill operations; also to insure a thorough even heat through a cross-section of the steel. This heat also causes blanks with seams or slight flaws to open up in quenching, making detection of defective blanks very easy. The quenching oil was kept at a constant temperature of 100°F., to avoid subjecting the steel to shocks, thereby causing surface cracks. The drawing of temper was the most critical operation and was kept within a 10° fluctuation. The degree of heat necessary depends entirely on the analysis of the steel, there being a certain variation in the different heats of steel as received from the mill. MACHINEABILITY Reheating for machineability was done at 100° less than the drawing temperature, but the time of soaking is more than double. After both drawing and reheating, the blanks were buried in lime where they remain, out of contact with the air, until their temperature had dropped to that of the workroom. For straightening, the barrels were heated to from 900 to 1,000°F. in an automatic furnace 25 ft. long, this operation taking about 2 hr. The purpose of hot straightening was to prevent any stresses being put into the blanks, so that after rough-turning, drilling or rifling operations they would not have a tendency to spring back to shape as left by the quenching bath. A method that produces an even better machining rifle blank, which practically stays straight through the different machining operations, was to rough-turn the blanks, then subject them to a heat of practically 1,000° for 4 hr. Production throughout the different operations is materially increased, with practically no straightening being from drilling, reaming, finish-turning or rifling operations. THE FORGING OF STEEL 73 74 THE WORKING OF STEEL This method was tested out by one of the largest manufacturers and proved to be the best way to eliminate a very expensive finished gun-barrel straightening process. The heat-treating required a large amount of cooling oil, and the problem of keeping this at the proper temperature required considerable study. The result was the cooling plant on the roof, as shown in Figs. 22, 23 and 24. The first two illustrations show the plant as it appeared complete. Figure 24 shows how the oil was handled in what is sometimes called the ebulator system. The oil was pumped up from the cooling tanks through the pipe A to the tank B. From here it ran down onto the ^- 5' _^-, •SWaI" FrnmMI «"AV from Oil %%~ ' Pump |* Fig. 24. — Details of the cooler. breakers or separators C, which break the oil up into fine particles that are caught by the fans D. The spray is blown up into the cooling tower E, which contains banks of cooling pipes, as can be seen, as well as baffles F. The spray collects on the cool pipes and forms drops, which fall on the curved plates G and run back to the oil-storage tank below ground. The water for this cooling was pumped from 10 artesian wells at the rate of 60 gal. per minute and cooled 90 gal. of oil per minute, lowering the temperature from 130 or 140 to 100°F. The water as it came from the wells averaged around 52°F. The motor was of a 7^-hp. variable-speed type with a range of from 700 to 1,200 r.p.m., which could be varied to suit the amount of oil to be cooled. The plant handled 300 gal. of oil per minute. CHAPTER VI ANNEALING There is no nrystery or secret about the proper annealing of different steels, but in order to secure the best results it is abso- lutely necessary for the operator to know the kind of steel which is to be annealed. The annealing of steel is primarily done for one of three' specific purposes: To soften for machining purposes; to change the physical properties, largely to increase ductility; or to release strains caused b}~ rolling or forging. Proper annealing means the heating of the steel slowly and uniformly to the right temperature, the holding of the tempera- ture for a given period and the gradual cooling to normal tem- perature. The proper temperature depends on the kind of steel, and the suggestions of the maker of the special steel being used should be carefully followed. For carbon steel the tem- peratures recommended for annealing vary from 1,200 to 1,450°F. This temperature need not be long continued. The steel should be cooled in hot sand, lime or ashes. If heated in the open forge the steel should be buried in the cooling material as quickly as possible, not allowing it to remain in the open air any longer than absolutely necessary. Best results, however, are secured when the fire does not come in direct contact with the steel. Good results are obtained by packing the steel in iron boxes or tubes, much as for case-hardening or carbonizing, using the same materials. They do not require separation for annealing, however. Do not remove from boxes until cold. Steel to be annealed may be classified into four different groups, each of which must be treated according to the elements con- tained in its particular class, and different methods are therefore necessary to bring about the desired result. The classifications are as follows: High-speed steel, alio}'' steel, tool or crucible steel, and high-carbon machinery steel. ANNEALING OF HIGH-SPEED STEEL For annealing high-speed steel, some makers recommend using ground mica, charcoal, lime, fine dry ashes or lake sand as a packing in the annealing boxes. Mixtures of one part charcoal, 76 THE WORKING OF STEEL one part lime and three parts of sand are also suggested, or two parts of ashes may be substituted for the one part of lime. To bring about the softest structure or machineability of high- speed steel, it should be packed in charcoal in boxes or pipes, carefully sealed at all points, so that no gases will escape or air be admitted. It should be heated slowly to not less than 1,450°F. and the steel must not be removed from its packing until it is cool. Slow heating means that the high heat must have pene- trated to the very core of the steel. When the steel is heated clear through it has been in the fur- nace long enough. If the steel can remain in the furnace and cool down with it, there will be no danger of air blasts or sudden or uneven cooling. If not, remove the box and cover quickly with dry ashes, sand or lime until it becomes cold. Too high a heat or maintaining the heat for too long a period, produces a harsh, coarse grain and greatly increases the liability to crack in hardening. It also reduces the strength and tough- ness of the steel. Steel which is to be used for making tools with teeth, such as taps, reamers and milling cutters, should not be annealed too much. When the steel is too soft it is more apt to tear in cutting and makes it more difficult to cut a smooth thread or other surface. Moderate annealing is found best for tools of this kind. TOOL OR CRUCIBLE STEEL Crucible steel can be annealed either in muffled furnace or by being packed. Packing is by far the most satisfactory method as it prevents scaling, local hard spots, uneven annealing, or violent changes in shape. It should be brought up slowly to just above its calescent or hardening temperature. The operator must know before setting his heats the temperature at which the differ- ent carbon content steels are hardened. The higher the carbon contents the lower is the hardening heat, but this should in no case be less than 1,400°F. ANNEALING ALLOY STEEL The term alloy steel from the steel maker's point of view, refers largely to nickel and chrome steel or a combination of both. These steels are manufactured very largely by the open hearth process. Although chromium steels are also a crucible product, it is next to impossible to give proper directions for the proper ANNEALING 77 annealing of alloy steel unless the four principal elements con- tained in such steels are known to the operator. These four elements are: carbon, manganese, chromium and nickel. Each element is a deciding factor in hardening such steel and therefore the proper annealing is of great importance. In annealing this steel, however, not much importance need be laid to the carbon content. The length of time or the temperature is in direct proportion to its chromium and nickel contents. The chromium content decides the degree of temperature and the amount of nickel decides the time required for thorough penetration and proper changing or mixing of the elements. A steel with a content of 20 points each of chromium and nickel, and from 60 to 90 points of manganese, requires not less than 1,350°F. HIGH-CARBON MACHINERY STEEL The carbon contents of this steel is above 30 points and is hardly ever above 100 points or 1 per cent. Annealing such steel is generally one of quantity production and does not require the care that the other steels need because it is very largely a much cheaper product and a great deal of material is generally removed from the outside surface. The purpose for which this steel is annea^d is a deciding- factor as to what heat to give it. If it is for machineability only, the steel requires to be brought up slowly to not less than 1,300°F. and then slowly cooled in the furnace or ash pit. It must be thoroughly covered so that there will be no access of cool air. If the annealing is to increase ductility or to affect some other physical property of the steel, it should be slowly heated to between 1,100 and 1,200°F. and kept at this heat for a length of time necessary for a thorough penetration to the core, after which it can be removed and put in an ash pit or covered with lime. If the annealing is just to relieve strains, slow heating is not necessary, but the steel must be brought up to a temperature not much less than a forging or rolling heat and gradually cooled. Covering in this case is only necessary in steel of a carbon content of more than 40 points. ANNEALING IN BONE ' Steel and cast iron may both be annealed in granulated bone. Pack the work the same as for case-hardening except that it is not necessary to keep the pieces away from each other. Pack 78 THE WORKING OF STEEL with bone that has been used until it is nearly white. Heat as hot as necessary for the steel and let the furnace cool down. If the boxes are removed from furnace while still warm, cover boxes and all in warm ashes or sand, air slaked lime or old, burned bone to retain heat as long as possible. Do not remove work from boxes until cold. ANNEALING OF RIFLE COMPONENTS AT SPRINGFIELD ARMORY In general, all forgings of the components of the arms manu- factured at the Armory and all forgings for other ordnance estab- lishments are packed in charcoal, lime or suitable material and annealed before being transferred from the forge shop. Except in special cases, all annealing will be done in annealing pots of appropriate size. One fire end of a thermo-couple is inserted in the center of the annealing pot nearest the middle of the furnace and another in the furnace outside of but near the annealing pots. The temperatures used in annealing carbon steel components of the various classes used at the Armory vary from 800°C. to 880°C. or 1,475 to 1,615°F. The fuel is shut off from the annealing furnace gradually as the temperature of the pot approaches the prescribed annealing temperature so as to prevent heating beyond that temperature. The forgings of the rifle barrel and the pistol barrel are excep- tions to the above general rule. These forgings will be packed in lime and allowed to cool slowly from the residual heat after forging. CHAPTER VII CASE-HARDENING OR SURFACE-CARBURIZING Carburizing, commonly called case-hardening, is the art of producing a tool-steel surface, or case, upon a machinery steel article. Wrenches, locomotive link motions, gun mechanisms, balls and ball races, automobile gears and many other devices are thereby given a high-carbon case capable of assuming extreme hardness, while the interior body of metal, the core, remains soft and tough. The simplest method is to heat the piece to be hardened to a bright red, dip it in cyanide of potassium (or cover it by sprin- kling the cyanide over it), keep it hot until the cyanide covers it thoroughly, and quench in water. This converts the outer skin into steel and hardens this skin but leaves the center soft. The hard surface or "case" varies in thickness according to the size of the piece, the materials used and the length of time which the piece remains at the carburizing temperature. Cyanide case- hardening is used only where a light or thin skin is sufficient. It gives a thickness of about 0.002 in. The penetration of carbon- izing will be given later. In some cases of cyanide carburizing, the piece is heated in cyanide to the desired temperature and then quenched. For a thicker case the steel is packed in carbon materials of various kinds such as burnt leather scraps, charcoal, granulated bone or some of the many carbonizing compounds. Machined or forged steel parts are packed with case-hardening material in metal boxes and subjected to a red heat. Under such conditions, carbon is absorbed by the steel surfaces, and a carburized case is produced capable of responding to ordinary hardening and tempering operations, the core meanwhile retain- ing its original softness and toughness. Such case-hardened parts are stronger, cheaper, and more serviceable than similar parts made of tool steel. The tough core resists breakage by shock. The hardened case resists wear from friction. The low cost of material, the ease of manu- facture, and the lessened breakage in quenching all serve to promote cheap production. 79 80 THE WORKING OF STEEL For successful carburizing, the following points should be carefully observed: The utmost care should be used in the selection of pots for carburizing; they should be as free as possible from both scaling and warping. These two requirements eliminate the cast iron pot, although many are used, thus leaving us to select from Fig. 25. Fig. 26. -• <§ • © #j •[©"©liiGL: o[o^if- 4= fl=* Fig. 27. Fig. 28. Figs. 25 to 28. — Case-hardening or carburizing boxes. D> Fig. 29. — A lid that is easily luted. malleable castings, wrought iron, cast steel, and special alloys, such as nichrome or silchrome. If first cost is not important, it will prove cheaper in the end to use pots of some special alloy. The pots should be standardized to suit the product. Pots should be made as small as possible in width, and space gained by increasing the height; for it takes about 1% hr. to heatthe CASE-HARDENING OR SURFACE-CARBONIZING 81 average small pot of 4 in. in width, between 3 and 4 hr. to heat to the center of an 8-in. box, and 5 to 6 hr. to heat to the center of a 12-in. box; and the longer the time required to heat to the center, the more uneven the carburizing. The work is packed in the box surrounded by materials which will give up carbon when heated. It must be packed so that each piece is separate from the others and does not touch the box, with a sufficient amount of carburizing material surrounding each. Figures 25 to 29 show the kind of boxes used and the way the work should be packed. Figure 29 shows a later type of box in which the edges can be easily luted. Figure 28 shows how test wires are used to determine the depth of case. Figure 26 shows the minimum clearance which should be used in packing and Fig. 27 the way in which the outer pieces receive the heat first and likewise take up the carbon before those in the center. This is why a slow, soaking heat is necessary in handling large quantities of work, so as to allow the heat and carbon to soak in equally. The temperature depends upon the carbon contents of the steel being treated and the length of time upon the depth of case required. The temperature range is about as follows: Per cent carbon "Points " of carbon Degrei 3S Fahi 0.10 10 1,616 0.20 20 1,562 0.30 30 1,535 0.40 40 1,508 0.50 50 1,492 0.60 60 1,481 0.70 70 1,476 . 80 to 1 5 80 to 150 1,472 The most important thing in carburizing is the human element. Most careful vigilance should be kept when packing and unpack- ing, and the operator should be instructed in the necessity for clean compound free from scale, moisture, fire clay, sand, floor sweepings, etc. From just such causes, many a good carburizer has been unjustly condemned. It is essential with most carbu- rizers to use about 25 to 50 per cent of used material, in order to prevent undue shrinking during heating; therefore the necessity of properly screening used material and carefully inspecting it for foreign substances before it is used again. It is right here that the greatest carelessness is generally encountered. 6 82 THE WORKING OF STEEL Don't pack the work to be carburized too closely; leave at least 1 in. from the bottom, % in. from the sides, and 1 in. from the top of pots, and for a 6-hr. run, have the pieces at least % in. apart. This gives the heat a chance to thoroughly permeate the pot, and the carburizing material a chance to shrink without allowing carburized pieces to touch and cause soft spots. Good case-hardening pots and annealing tubes can be made from the desired size of wrought iron pipe. The ends are capped or welded, and a slot is cut in the side of the pot, equal to one quarter of its circumference, and about % of its length. Another piece of the same diameter pipe cut lengthwise into thirds forms a cover for this pot. We then have a cheap, substantial pot, non-warping, with a minimum tendency to scale. This idea is especially adaptable when long, narrow pots are desired, and works out very successfully. When pots are packed and the carburizer thoroughly tamped down, the covers of the pot are put on and sealed with fire clay which has a little salt mixed into it. The more perfect the seal the more we can get out of the carburizer. The rates of pene- tration depend on temperature and the presence of proper gas in the required volume. Any pressure we can cause will, of course, have a tendency to increase the rate of penetration. If you have a wide furnace, do not load it full at one time. Put one-half your load in first, in the center of the furnace, and heat until pots show a low red, about 1,325 to 1,350°F. Then fill the furnace by putting the cold pots on the outside or, the section nearest the source of heat. This will give the work in the slowest portion of the furnace a chance to come to heat at the same time as the pots that are nearest the sources of heat. To obtain an even heating of the pots and lessen their tendency to warp and scale, and to cause the contents of the furnace to heat up evenly, we should use a reducing fire and fill the heating chamber with flame. This can be accomplished by partially closing the waste gas vents and reducing slightly the amount of air used by the burners. A short flame will then be noticed issuing from the partially closed vents. Thus, while maintain- ing the temperature of the heating chamber, we will have a lower temperature in the combustion chamber, which will naturally increase its longevity. It is always advisable to allow work to cool in the pots. This saves compound, and causes a more gradual diffusion of the carbon CASE-HARDENING OR SURFACE-CARBONIZING 83 between the case and the core, and is very desirable condition, inasmuch as abrupt cases are inclined to chip out. The most satisfactory steel to carburize contains between 0.10 and 0.20 per cent carbon, less than 0.35 per cent manganese, less than 0.04 per cent phosphorus and sulphur, and low silicon. But steel of this composition does not seem to satisfy our pro- gressive engineers, and many alloy steels are now on the market, these, although more or less difficult to machine, give when carburized the various qualities demanded, such as a very hard case, very tough core, or very hard case and tough core. How- ever, the additional elements also have a great effect both on the rate of penetration during the carburizing operation, and on the final treatment, consequently such alloy steels require very care- ful supervision during the entire heat treating operations. RATE OF ABSORPTION According to Guillet, the absorption of carbon is favored by those special elements which exist as double carbides in steel. For example, manganese exists as manganese carbide in combina- tion with the iron carbide. The elements that favor the absorption of carbon are: manganese, tungsten, chromium and molybdenum those opposing it, nickel, silicon, and aluminum. Guillet has worked out the effect of the different elements on the rate of penetration in comparison with steel that absorbed carbon at a given temperature, at an average rate of 0.035 in. per hour. His tables show that the following elements require an in- creased time of exposure to the carburizing material in order to obtain the same depth of penetration as with simple steel: When steel contains Increased time of exposure 2 . per cent nickel 28 per cent 7.0 per cent nickel. . 30 per cent 1 . per cent titanium 12 per cent 2 . per cent titanium 28 per cent 0.5 per cent silicon 50 per cent 1 . per cent silicon 80 per cent 2.0 per cent silicon 122 per cent 5 . per cent silicon No penetration 1 . per cent aluminum 122 per cent 2 . per cent aluminum 350 per cent The following elements seem to assist the rate of penetration of carbon, and the carburizing time may therfore be reduced as follows : 84 THE WORKING OF STEEL When steel contains Decreased time of exposure 0.5 per cent manganese 18 per cent 1 . per cent manganese 25 per cent 1 . per cent chromium 10 per cent 2.0 per cent chromium IS per cent . 5 per cent tungsten 1 . per cent tungsten 2 . per cent tungsten 25 per cent 1 . per cent molybdenum 2.0 per cent molybdenum 18 per cent The temperature at which carburization is accomplished is a very important factor. Hence the necessity for a reliable pyro- meter, located so as to give the temperature just below the tops of the pots. It must be remembered, however, that the pyrometer gives the temperature of only one spot, and is therefore only an aid to the operator, who must use his eyes for successful results. The carbon content of the case generally is governed by the temperature of the carburization. It generally proves advisable to have the case contain between 0.90 per cent and 1.10 carbon; more carbon than this gives rise to excess free cementite or carbide of iron, which is detrimental, causing the case to be brittle and apt to chip. T. G. Selleck gives a very useful table of temperatures and the relative carbon contents of the case of steels carburized between 4 and 6 hrs. using a good charcoal carburizer. This data is as follows : Table 15. — Carbon Content Obtained at Various Temperatures At 1,500°F., the surface carbon content will be 0.90 per cent At 1,600°F., the surface carbon content will be 1 . 00 per cent At 1,650°F., the surface carbon content will be 1 . 10 per cent At 1,700°F., the surface carbon content will be 1 .25 per cent At 1,750°F., the surface carbon content will be 1.40 per cent At 1,800°F., the surface carbon content will be 1 .75 per cent To this very valuable table, it seems best to add the following data, which we have used for a number of years. We do not know the name of its author, but it has proved very valuable, and seems to complete the above information. The table is self- explanatory, giving depth of penetration of the carbon of the case at different temperatures for different lengths of time: CASE-HARDENING OR SURFACE-CARBURIZING 85, Penetration Temperature 1,550 1,650 1,800 Penetration after % nr - Penetration after 1 hr. . Penetration after 2 hr. . Penetration after 3 hr. . Penetration after 4 hr. . Penetration after 6 hr. . 0.008 0.018 0.035 0.045 0.052 0.056 Penetration after 8 hr. 0. 062 0.012 0.026 0.048 0.055 0.061 0.075 0.083 0.030 0.045 0.060 0.075 0.092 0.110 0.130 From the tables given, we may calculate with a fair degree of certainty the amount of carbon in the case, and its penetration. The facts can be very readily checked by an examination of samples with the microscope. CARBURIZING MATERIAL The simplest carburizing substance is pure carbon. It is also the most inefficient, but can be used if mixed with something that will evolve carbon monoxide or nitrogen gas on being heated. A great variety of materials is used in carburizing mixtures, a few of them being charcoal (both wood and bone), charred leather, crushed bone, horn, mixtures of charcoal and barium carbonate, coke and heavy oils, coke treated with alkaline carbonates, peat, charcoal mixed with common salt, saltpeter, resin, flour, potas- sium, bichromate, vegetable fibre, limestone, various seed husks, etc. H. L. Heathcote, on analyzing seventeen different carburizers, found that they contained the following ingredients: Per cent Moisture 2 . 68 to 26 . 17 Oil 0.17 to 20.76 Carbon (organic) 6 . 70 to 54 . 19 Calcium phosphate 0.32 to 74. 75 Calcium carbonate 1 . 20 to 11 . 57 Barium carbonate nil to 42 . 00 Zinc oxide nil to 14 . 50 Silica nil to 8.14 Sulphates (S0 3 ) trace to 3.45 Sodium chloride nil to 7.88 Sodium carbonate nil to 40.00 Sulphides (S) nil to 2.80 86 THE WORKING OF STEEL Carburizing mixtures, though bought by weight, are used by volume, and the weight per cubic foot is a big factor in making a selection. A good mixture should be porous, so that the evolved gases, which should be generated at the proper temperature, may move freely around the steel objects being carburized; should be a good conductor of heat; should possess minimum shrinkage when used; and should be capable of being tamped down. Mr. Heathcote also claims that by " incorporating a little potassium carbonate with exhausted charcoal is found to restore at once its carburizing power and make it give up its carbon more readily than the original charcoal." The same is true when potas- sium hydrate or sodium carbonate is incorporated. QUENCHING It is generally considered good practice to quench from the pot, especially if the case is of any appreciable depth. The tex- Fig. 30. — Case-hardening depths. ture of the steel has been weakened by the prolonged high heat of carburizing, so that if we need a tough core, we must treat it above its critical range, which is about 1,600°F. for simple steel, but lower for manganese and nickel steels. Quenching is done in either water, oil, or air, depending upon the results desired. The steel is then very carefully reheated to refine the case, the temperature varying from 1,350 to 1,450°F., depending on whether the material is an alloy or a simple steel, and quenched in either water or oil. There are many possibilities yet to be developed with the car- burizing of alloy steels, which can produce a very tough, tenacious CASE-HARDENING OR SURFACE-CARBURIZING 87 austenitic case which becomes hard on cooling in air, and still retain a soft, pearlitic core. An austenitic case is not necessarily file hard, but has a very great resistance to abrasive wear. The more carbon a steel has to begin with the more slowly will it absorb carbon and the lower the temperature required. Low carbon steel of from 15 to 20 points is generally used and the carbon brought up to 80 or 85 points. Tool steels may be carbon- ized as high as 250 points but this is seldom if ever required. In addition to the carburizing materials given, a mixture of 40 per cent of barium carbonate and 60 per cent charcoal gives much faster penetration than charcoal, bone or leather. The penetra- tion of this mixture on ordinary low-carbon steel is shown in Fig. 30, over a range of from 2 to 12 hr. EFFECT OF DIFFERENT CARBURIZING MATERIAL Each of these different packing materials has a different effect upon the work in which it is heated. Charcoal by itself will give Fig. 31. Fig. 32. Fig. 33. Spent Fig. 35. Fig. 34. Figs. 31 to 35. a rather light case. Mixed with raw bone it will carburize more rapidly, and still more so if mixed with burnt bone. Raw bone and burnt bone, as may be inferred, are both quicker carbonizers than charcoal, but raw bone must never be used where the break- age of hardened edges is to be avoided, as it contains phosphorus and tends to make the piece brittle. Charred leather mixed with charcoal is a still faster material, and horns and hoofs exceed even this in speed; but these two compounds are restricted by their cost to use with high-grade articles, usually of tool or high-carbon steel, that are to be hardened locally — that is, "pack-hardened." 88 THE WORKING OF STEEL Cyanide of potassium and prussiate of potash are also included in the list of carbonizing materials; but outside of carburizing by dipping into melted baths of these materials, their use is largely confined to local hardening of small surfaces, such as holes in dies and the like. One of the advantages of hardening by carburizing is the fact that you can arrange to leave part of the work soft and thus retain the toughness and strength of the original material. Figures 31 to 35 show ways of doing this. The inside of the cup in Fig. 32 is locally hardened, as illustrated in Fig. 32, "spent" or used bone being packed around the surfaces that are to be left soft, while cyanide of potassium is put around those which are desired hard. The threads of the nut in Fig. 33 are kept soft by carbur- izing the nut while upon a stud. The profile gage, Fig. 34, is made of high-carbon steel and is hardened on the inside by pack- ing with charred leather, but kept soft on the outside by surround- ing it with fireclay. The rivet stud shown in Fig. 35 is carburized while of its full diameter and then turned down to the size of the rivet end, thus cutting away the carburized surface. Pieces of this kind are of course not quenched and hardened in the carburizing heat, but are left in the box to cool, just as in box annealing, being reheated and quenched as a second operation. In fact, this is a good scheme to use for the majority of carburizing work of small and moderate size. Sometimes it is desired to harden a thin piece of sheet steel halfway through, retaining the soft portion as a backing for strength. Material is on the market with which one side of the steel can be treated; or copper-plating one side of it will answer the same purpose and prevent that side becoming carburized. QUENCHING THE WORK In some cases case-hardened work is quenched right from the box by dumping the whole contents into the quenching tank. It is common practice to leave a sieveor wire basket to catch the work, allowing the carburizing material to fall to the botom of the tank where it can be recovered later and used again as a part of a new mixture. For best results, however, the steel is allowed to cool down slowly in the box after which it is removed and hardened by heating and quenching the same as carbon steel of the same grade. It has absorbed sufficient carbon so that, in the outer portions at least, it is a high-carbon steel. CASE-HARDENING OR SURF AC E-CARBURI ZING 89 After packing the work carefully in the boxes the lids are sealed or luted with fireclay to keep out any gases from the fire. The size of box should be proportioned to the work. The box should not be too large especially for light work that is run on a short heat. If it can be just large enough to allow the proper amount of material around it, the work is apt to be more satisfactory in every way. The first or carburizing heat toughens the core. The reheat- ing temperature, that is the heating for quenching, can usually be about 200° lower than the first heat. Large work may re- quire 25° to 50° more heat than small work to secure the same results. The effect of size is treated in detail on page 117. CASE-HARDENING CAST IRON It is claimed that cast iron can also be hardened on the surface but that as it does not add to its strength its uses are limited to such pieces as gages and templets. Experience indicates, how- ever^ that the iron casting must be made malleable by long and uniform heating before it can be hardened. When this is done the surface can be given a surface hardness by using the follow- ing formula: To 20 gal. of water add 1 pt. of oil of vitrol, 2 pk. of salt, 4 lb. of alum, Y^ lb. of yellow prussiate of potash, ^ lb. cyanide of pot- ash and 1 lb. of salt peter. This should be kept in a covered wooden barrel. The casting to be hardened should be heated to a cherry red and then plunged into this bath which hardens the surface. It is sometimes necessary to repeat the operation two or three times to get the surface sufficiently hard. THE QUENCHING TANK The quenching tank is an important feature of apparatus in case-hardening — possibly more so than in ordinary tempering. One reason for this is because of the large quantities of pieces usually dumped into the tank at a time. One cannot take time to separate the articles themselves from the case-hardening mixture, and the whole content of the box is droped into the bath in short order, as exposure to air of the heated work is fatal to results. Unless it is split up, it is likely to go to the bottom as a solid mass, in which case very few of the pieces are properly hardened. 90 THE WORKING OF STEEL A combination cooling tank is shown in Fig. 36. Water inlet and outlet pipes are shown and also a drain plug that enables the tank to be emptied when it is desired to clean out the spent car- burizing material from the bottom. A wire-bottomed tray, framed with angle iron, is arranged to slide into this tank from the top and rests upon angle irons screwed to the tank sides. Its function is to catch the pieces and prevent them from settling to the tank bottom, and it also makes it easy to remove a batch of work. A bottomless box of sheet steel is shown at C. This Fig. 36. — Combination cooling tank for case-hardening. fits into the wire-bottomed tray and has a number of rods or wires running across it, their purpose being to break up the mass of material as it comes from the carbonizing box. Below the wire-bottomed tray is a perforated cross-pipe that is connected with a compressed-air line. This is used when case- hardening for colors. The shop that has no air compressor may rig up a satisfactory equivalent in the shape of a low-pressure hand-operated air pump and a receiver tank, for it is not neces- sary to use high-pressure air for this purpose. When colors are desired on case-hardened work, the treatment in quenching is CASE-HARDENING OR SURFACE-CARBURIZING 91 Untreated Steel fine grained and lough, CUb 'to 020% Carbon .Case 30% to 90% Carbon ■Case hard and brittle exactly the same as that previously described except that air is pumped through this pipe and keeps the water agitated. The addition of a slight amount of powdered cyanide of potassium to the packing material used for carburizing will produce stronger colors, and where this is the sole object, it is best to maintain the box at a dull-red heat. The old way of case-hardening was to dump the contents of the box at the end of the carburizing heat. Later study in the structure of steel thus treated has caused a change in this procedure, the use of automobiles and alloy steels probably hastening this Za t^^™^ result. The diagrams reproduced in Fig. 37 show why the heat treatment of case-hardened work is necessary. Starting at A with a close-grained and tough stock, such as ordinary machinery steel containing from 15 to 20 points of carbon, if such work is quenched on a carbonizing heat the result will be as shown at B. This gives a core that is coarse-grained and brittle and an outer case that is fine-grained and hard, but is likely to flake off, owing to the great difference in structure between it and the core. Reheating this work beyond the critical temperature of the core re- fines this core, closes the grain and makes it tough, but leaves the case Very brittle; ment f case-hardened work in fact, more so than it was before. sCasedO% to90% Carbon Case brjnie and "very hard Core fine grained and tough, 015%to 020% Carbon Reheated to refine the Core Reheated to l500Deg.F Quenched in Water Fig ■Case S0%to90% Carbon -Case tough and hard Core fine grained and tough,/5%toZO% Carbon Reheated to toughen the Case Why heat treat- REF1NING THE GRAIN This is remedied by reheating the piece to a temperature slightly above the critical temperature of the case, this tempera- ture corresponding ordinarily to that of steel having a carbon content of 85 points. When this is again quenched, the tempera- ture, which has not been high enough to disturb the refined core, will have closed the grain of the case and toughened it. So, instead of but one heat and one quenching for this class of work, we have three of each, although it is quite possible and often profitable to omit the quenching after carburizing and allow the 92 THE WORKING OF STEEL piece or pieces and the case-carburizing box to cool together, as in annealing. Sometimes another heat treatment is added to the foregoing, for the purpose of letting down the hardness of the case and giving it additional toughness by heating to a tempera- ture between 300° and 500°. Usually this is done in an oil bath. After this the piece is allowed to cool. It is possible to harden the surface of tool steel extremely hard and yet leave its inner core soft and tough for strength, by a process similar to case-hardening and known as "pack-harden- ing." It consists in using tool steel of carbon contents ranging from 60 to 80 points, packing this in a box with charred leather mixed with wood charcoal and heating at a low-red heat for 2 or 3 hr., thus raising the carbon content of the exterior of the piece. The article when quenched in an oil bath will have an extremely hard exterior and tough core. It is a good scheme for tools that must be hard and yet strong enough to stand abuse. Raw bone is never used as a packing for this class of work, as it makes the cutting edges brittle. CASE-HARDENING TREATMENTS FOR VARIOUS STEELS Plain water, salt water and linseed oil are the three most common quenching materials for case-hardening. Water is used for ordinary work, salt water for work which must be extremely hard on the surface, and oil for work in which tough- ness is the main consideration. The higher the carbon of the case, the less sudden need the quenching action take hold of the piece; in fact, experience in case-hardening work gives a great many combinations of quenching baths of these three materials, depending on their temperatures. Thin work, highly carbonized, which would fly to pieces under the slightest blow if quenched in water or brine, is made strong and tough by properly quenching in slightly heated oil. It is impossible to give any rules for the temperature of this work, so much depending on the size and design of the piece; but it is not a difficult matter to try three or four pieces by different methods and determine what is needed for best results. The alloy steels are all susceptible of case-hardening treat- ment; in fact, this is one of the most important heat treatments for such steels in the automobile industry. Nickel steel carbu- rizes more slowly than common steel, the nickel seeming to have the effect of slowing down the rate of penetration. There is no CASE-HARDENING OR SURFACE-CARBURIZING 93 cloud without its silver lining, however, and to offset this retar- dation, a single treatment is often sufficient for nickel steel; for the core is not coarsened as much as low-carbon machinery steel and thus ordinary work may be quenched on the carburizing heat. Steel containing from 3 to 3.5 per cent of nickel is carbu- rized between 1,300 and 1,400°F. Nickel steel containing less than 25 points of carbon, with this same percentage of nickel, may be case-hardened by cooling in air instead of quenching. Chrome-nickel steel may be case-hardened similarly to the method just described for nickel steel, but double treatment gives better results and is used for high-grade work. The carburizing temperature is the same, between 1,300 and 1,400°F., the second treatment consisting of reheating to 1,400° and then quenching in boiling salt water, which gives a hard surface and at the same time prevents distortion of the piece. The core of chrome-nickel case-hardened steel, like that of nickel steel, is not coarsened excessively by the first heat treatment, and therefore a single heating and quenching will suffice for ordinary work. CARBURIZING BY GAS The process of carburizing by gas consists of having a slowly revolving, properly heated, cylindrical retort into which carburiz- ing gas is injected under pressure. The volatile carbon in the gas is easily absorbed, fresh gas being admitted and the spent gases are vented to insure the greatest speed in carbonizing. The work is constantly and uniformly exposed to an atmosphere of carbon instead of the solid carbons which turn to ash. The absorption of carbon begins as soon as the work heats sufficiently. Originally this process required a gas generator but this has been obviated in later machines. The gas consists of carbon vapor derived from petroleum, diluted by a neutral gas in such proportion that the carbon is supplied to the work as fast as it can be absorbed without forming obstructive deposits. PREVENTING CARBURIZING BY COPPER-PLATING Copper-plating has been found effective and must have a thick- ness of 0.0005 in. Less than this does not give a continuous coat- ing. The plating bath used had a temperature of 170°F. and at voltage of 4.1. The operation is as follows: 94 THE WORKING OF STEEL Operation No. Contents of bath ■ Purpose 1 Gasolene To remove grease 2 Sawdust To dry 3 Warm potassium hydroxide solution To remove grease and dirt 4 ■Warm water Warm sulphuric acid solution To wash 5 To acid clean 6 Warm water To wash 7 Cold water Additional wash 8 Cold potassium cyanide solution Cleanser 9 Cold water To wash 10 Electric cleaner, warm sodium hy- Cleanser to give good droxide case-iron anode plating surface 11 Copper plating both of copper sul- phate and potassium cyanide solu- tion warm Plating bath There are also other methods of preventing case-hardening, one being to paint the surface with a special compound prepared for this purpose. In some cases a coating of plastic asbestos is used while in others thin sheet asbestos is wired around the part to be kept soft. PREPARING PARTS FOR LOCAL CASE-HARDENING At the works of the Dayton Engineering Laboratories Com- pany, Dayton, Ohio, they have a large quantity of small shafts, Ve.-0.84"--- 040SL o.40 fr- 2.332" "2.333'- r ~ -H O.I77"-0.)78" Ream must not be over am" of f ' 0.4985" Grind 0.4990" T — T A cf< $^0,375" Max. h - 3.257"—- — Fig. 38. — Shaft to be coated with paraffin Turn this End' after Carbonizing I ----- — >l Fig. 38, that are to be case-hardened at A while the ends B and C are to be left soft. Formerly, the part A was brush-coated with melted paraffin but, as there were many shafts, this was tedious and great care was necessary to avoid getting paraffin where it was not wanted. To insure uniform coating the device shown in Fig. 39 was made. Melted paraffin is poured in the well A and kept liquid by setting the device on a hot plate, the paraffin being kept high CASE-HARDENING OR SURF AC E-CARBURI ZING 95 enough to touch the bottoms of the rollers. The shaft to be coated is laid between the rollers with one end against the gage B, when a turn or two of the crank C will cause it to be evenly- coated. Fig. 39. — Device for coating the shaft. THE PENETRATION OF CARBON Carburized mild steel is used to a great extent in the manu- facture of automobile and other parts which are likely to be subjected to rough usage. The strength and ability to withstand hard knocks depend to a very considerable degree on the thorough- ness with which the carburizing process is conducted. Many automobile manufacturers have at one time or another passed through a period of unfortunate breakages, or have found that for a certain period the parts turned out of their hardening shops were not sufficiently hard to enable the rubbing surfaces to stand up against the pressure to which they were subjected. 96 THE WORKING OF STEEL So many factors govern the success of hardening that often this succession of bad work has been actually overcome without those interested realizing what was the weak point in their system of treatment. As the question is one that can create a bad reputation for the product of any firm it is well to study the influential factors minutely. INTRODUCTION OF CARBON The matter to which these notes are primarily directed is the introduction of carbon into the case of the article to be hardened. In the first place the chances of success are increased by selecting as few brands of steel as practicable to cover the requirements of each component of the mechanism. The hardener is then able to become accustomed to the characteristics of that particular material, and after determining the most suitable treatment for it no further experimenting beyond the usual check-test pieces is necessary. Although a certain make of material may vary in composition from time to time the products of a manufacturer of good steel can be generally relied upon, and it is better to deal directly with him than with others. In most cases the case-hardening steels can be chosen from the following: (1) Case-hardening mild steel of 0.10 per cent caibon; (2) case-hardening mild steel of 0.15 per cent carbon; (3) case- hardening nickel steel of 2 per cent nickel; (4) case-hardening nickel steel of 5 per cent nickel. After having chosen a suitable steel it is best to have the sample analyzed by three metallurgists and also to have test pieces machined and pulled. To prepare samples for analysis place a sheet of paper on the table of a drilling machine, and with a %-m. diameter drill, machine a few holes about %-m. deep in various parts of the sample bar, collecting about 3 oz. of fine drillings free from dust. This can be placed in a bottle and dispatched to the metallurgist with instructions to search for carbon, silicon, manganese, sulphur, phosphorus and nickel. The results of the different tests should be carefully tabulated, and as there would most probably be some variation an average should be made as a fair basis of each element present, and the following tables may be used with confidence when deciding if the material is reliable enough to be used: CASE-HARDENING OR SVRFACE-CARBURIZING 97 Table 16. — Case-hardening Mild Steel of 0.10 Per Cent Carbon Carbon . 08 to . 14 per cent Silicon Not over . 20 per cent Manganese Not over . 06 per cent Sulphur Not over . 04 per cent Phosphorus Not over . 04 per cent A pull on a test bar ground to V4 sq. in. in area should register at least 6 tons, being equal to 24 tons per square inch. Table 17. — Case-hardening Mild Steel of 0.15 Per Cent Carbon Carbon . 12 to . 20 per cent Silicon Not over . 20 per cent Manganese . 65 to 1 per cent Sulphur Not over . 07 per cent Phosphorus Not over . 07 per cent Tensile breaking strength should be 25 to 33 tons per square inch. Table 18. — Case-hardening Nickel Steel of 2 Per Cent Nickel Carbon 0.10 to 0.15 per cent Silicon Not over . 30 per cent Manganese . 25 to . 50 per cent Sulphur Not over . 05 per cent Phosphorus Not over . 05 per cent Nickel 2 to 2 . 50 per cent Tensile breaking strength 25 to 35 tons per square inch. Table 19. — Case-hardening Nickel Steel of 5 Per Cent Nickei Carbon Not over . 15 per cent Silicon Not over . 20 per cent Manganese Not over . 04 per cent Sulphur Not over . 05 per cent Phosphorus Not over 0. 05 per cent Nickel 4 . 75 to 5 . 75 per cent Tensile breaking strength 25 to 40 tons per square inch. Having determined what is required we now proceed to inquire into the question of carburizing, which is of vital importance. USING ILLUMINATING GAS The choice of a carburizing furnace depends greatly on the facilities available in the locality where the shop is situated and the nature and quantity of the work to be done. The furnaces can be heated with producer gas in most cases, but when space is of value illuminating gas from a separate source of supply has some compensations. When the latter is used it is well to install a governor if the pressure is likely to fluctuate, particularly where the shop is at a high altitude or at a distance from the gas supply. Many furnaces are coke-fired, and although greater care is 7 98 THE WORKING OF STEEL required in maintaining a uniform temperature good results have been obtained. The use of electricity as a means of reaching the requisite temperature is receiving some attention, and no doubt it would make the control of temperature comparatively simple. However, the cost when applied to large quantities of work will, for the present at least, prevent this method from becoming popular. It is believed that the results obtainable with the electric furnace would surpass any others; but the apparatus seems apt to burn out quickly; besides the necessity for frequent rewiring makes it impracticable at present. The most elementary medium of carburization is pure carbon, but the rate of carburization induced by this material is very low, and other components are necessary to accelerate the process. Many mixtures have been marketed, each possessing its indi- vidual merits, and as the prices vary considerably it is difficult to decide which is the most advantageous. Absorption from actual contact with solid carbon is decidedly slow, and it is necessary to employ a compound from which gases are liberated, and the steel will absorb the carbon from the gases much more readily. Both bone and leather charcoal are more readily volatilized than wood charcoal, and although the high sulphur content of the leather is objectionable as being injurious to the steel, as also is the high phosphorus content of the bone charcoal, they are both preferable to the wood charcoal. By mixing bone charcoal with barium carbonate in the pro- portions of 60 per cent of the former to 40 per cent of the latter a very reliable compound is obtained. The temperature to which this compound is subjected causes the liberation of barium monoxide by contact with the charcoal with which it is surrounded. Many more elaborate explanations may be given of the actions and reactions taking place, but the above is a satisfactorjr guide to indicate that it is not the actual compound which causes carburization, but the gases released from the compound. Until the temperature of the muffle reaches about 300°C. carburization does not take place to any useful extent, and conse- quently it is advisable to avoid the use of any compound from which the carburizing gases are liberated much before that temperature is reached. In the case of steel containing nickel slightly higher temperatures may be used and are really necessary CASE-HARDENING OR SURFACE-CARBURIZING 99 if the same rate of carbon penetration is to be obtained, as the presence of nickel resists the penetration. At higher temperatures the rate of penetration is higher, but not exactly in proportion to the temperature, and the rate is also influenced by the nature of the material and the efficiency of the compound employed. The so-called saturation point of mild steel is reached when the case contains 0.90 per cent of carbon, but this amount is frequently exceeded. Should it be required to ascertain the amount of carbon in a sample at varying depths below the skin 04 ! c £ r R o +- 8. y 20 30 4< ) 5 ) 6 1 7 J 6 3 4) Degrees of Hardness Fig. 40. — Chart showing penetration of carbon. this can be done by turning off a small amount after carburizing and analyzing the turnings. This can be repeated several times, and it will probably be found that the proportion of carbon decreases as the test piece is reduced in diameter unless decar- burization has taken place. The chart, Fig. 40, is also a good guide. In order to use the chart it is necessary to harden the sample we desire to test as we would harden a piece of tool steel, and then test by scleroscope. By locating on the chart the point on the horizontal axis which represents the hardness of the sample the curve enables one to determine the approximate amount of carbon present in the case. 100 THE WORKING OF STEEL Should the hardness lack uniformity the soft places can be identified by etching. To accomplish this the sample should be polished after quenching and then washed with a weak solution of nitric acid in alcohol, whereupon the harder points will show up darker than the softer areas. The selection of suitable boxes for carburizing is worthy of a little consideration, and there can be no doubt that in certain cases results are spoiled and considerable expense caused by using unsuitable containers. As far as initial expense goes cast-iron boxes are probably the most expedient, but although they will withstand the necessary temperatures they are liable to split and crack, and when they get out of shape there is much difficulty in straightening them. The most suitable material in most cases is steel boiler plate % or 3^ in. thick, which can be made with welded joints and will last well. The sizes of the boxes employed depend to a great extent on the nature of the work being done, but care should be exercised to avoid putting too much in one box, as smaller ones permit the heat to penetrate more quickly, and one test piece is sufficient to give a good indication of what has taken place. If it should be necessary to use larger boxes it is advisable to put in three or four test pieces in different positions to ascertain if the penetration of carbon has been satisfactory in all parts of the box, as it is quite possible that the temperature of the muffle is not the same at all points, and a record shown by one test piece would not then be applicable to all the parts contained in the box. It has been found that the rate of carbon penetration increases with the gas pressure around the articles being carburized, and it is therefore necessary to be careful in sealing up the boxes after packing. When the articles are placed within and each entirely surrounded by compound so that the compound reaches to within 1 in. of the top of the box a layer of clay should be run around the inside of the box on top of the compound. The lid, which should be a good fit in the box, is then to be pressed on top of this, and another layer of clay run just below the rim of the box on top of the cover. A SATISFACTORY LUTING MIXTURE A mixture of fireclay and sand will be found very satisfactory for closing up the boxes, and by observing the appearance of the CASE-HARDENING OR SURFACE-CARBURIZING 101 work when taken out we can gage the suitability of the methods employed, for unless the boxes are carefully sealed the work is generally covered with dark scales, while if properly done the articles will be of a light gray. By observing the above recommendations reliable results can be obtained, and we can expect uniform results after quenching. GAS CONSUMPTION FOR CARBURIZING Although the advantages offered by the gas-fired furnace for carburizing have been generally recognized in the past from points of view as close temperature regulation, decreased attendance, and greater convenience, very little information has been pub- lished regarding the consumption of gas for this process. It has therefore been a matter of great difficulty to obtain authentic information upon this point, either from makers or users of such furnaces. In view of this, the details of actual consumption of gas on a regular customer's order job will be of interest. The "Revergen" furnace, manufactured by the Davis Furnace Company, Luton, Bedford, England, was used on this job, and is provided with regenerators and fired with illuminating gas at ordinary pressure, the air being introduced to the furnace at a slight pressure of 3 to 4 in. water gage. The material was charged into a cold furnace, raised to 1,652°F., and maintained at that temperature for 8 hr. to give the necessary depth of case. The work consisted of automobile gears packed in six boxes, the total weight being 713 lb. The required temperature of 1,652°F. was obtained in 70 min. from lighting up, and a summary of the data is shown in the following table : Gas to raise furnace and charge from cold to 1,652°F., 70 min Gas to maintain 1,652°F. for 1st hour Gas to maintain 1,652°F. for 2nd hour Gas to maintain 1,652°F. for 3rd hour Gas to maintain 1,652°F. for 4th hour Gas to maintain 1,652°F. for 5th hour Gas to maintain 1,652°F. for 6th hour Gas to maintain 1,652°F. for 7th hour Gas to maintain 1,652°F. for 8th hour Cubic Foot Per Pound of Load Total Number of Cubic Foot 1.29 925 0.38 275 0.42 300 0.38 275 0.42 300 0.49 350 0.49 350 0.45 325 0.45 325 102 THE WORKING OF STEEL The overall gas consumption for this run of 9 hr. 10 min. was only 4.8 cu. ft. per pound of load. THE CARE OF CARBURIZ1NG COMPOUNDS Of all the opportunities for practicing economy in the heat- treatment department, there is none that offers greater possi- bilities for profitable returns than the systematic cleaning, blend- ing and reworking of artificial carburizers, or compounds. The question of whether or not it is practical to take up the work depends upon the nature of the output. If the sole product of the hardening department consists of a 1.10 carbon case or harder, requiring a strong highly energized material of deep penetrative power such as that used in the carburizing of ball races, hub-bearings and the like, it would be best to dispose of the used material to some concern whose product requires a case with from 0.70 to 0.90 carbon, but where there is a large variety of work the compound may be so handled that there will be practi- cally no waste. This is accomplished with one of the most widely known arti- ficial carburizers by giving all the compound in the plant three distinct classifications: "New," being direct from the maker; "half and half," being one part of new and one part first run; and "2 to 1," which consists of two parts of old and one part new. SEPARATING THE WORK FROM THE COMPOUND During the pulling of the heat, the pots are dumped upon a cast-iron screen which forms a table or apron for the furnace. Directly beneath this table is located one of the steel conveyor carts, shown in Fig. 41, which is provided with two wheels at the rear and a dolly clevis at the front, which allows it to be hauled away from beneath the furnace apron while filled with red- hot compound. A steel cover is provided for each box, and the material is allowed to cool without losing much of the evolved gases which are still being thrown off by the compound. As this compound comes from the carburizing pots it contains bits of fireclay which represent a part of the luting used for sealing, and there may be small parts of work or bits of fused material in it as well. After cooling, the compound is very dusty and CASE-HARDENING OR SURFACE-CARBURIZING 103 Fig. 41. — The cooling carts. Fig. 42. — Machine for blending the mixture. 104 THE WORKING OF STEEL disagreeable to handle, and, before it can be used again, must be sifted, cleaned and blended. Some time ago the writer was confronted with this proposition for one of the largest consumers of carburizing compound in the world, and the problem was handled in the following manner: The cooled compound was dumped from the cooling cars and sprinkled with a low-grade oil which served the dual purposes of settling the dust and adding a certain percentage of valuable hydrocarbon to the compound. In Fig. 42 is shown the machine that was designed to do the cleaning and blending. BLENDING THE COMPOUND Essentially, this consists of the sturdy, power-driven separator and fanning mill which separates the foreign matter from the compound and elevates it into a large settling basin which is formed by the top of the steel housing that incloses the apparatus. After reaching the settling basin, the compound falls by gravity into a power-driven rotary mixing tub which is directly beneath the settling basin. Here the blending is done by mixing the proper amount of various grades of material together. After blending the compound, it is ready to be stored in labeled con- tainers and delivered to the packing room. It will be seen that by this simple system there is the least possible loss of energy from the compound. The saving com- mences the moment the cooling cart is covered and preserves the valuable dust which is saved by the oiling and the settling basin of the blending machine. Then, too, there is the added convenience of the packers who have a thoroughly cleaned, dustless, and standardized product to work with. Of course, this also tends to insure uniformity in the case-hardening operation. With this outfit, one man cleans and blends as much compound in one hour as he formerly did in ten. CHAPTER VIII HEAT TREATMENT OF STEEL Heat treatment is a somewhat vague term. As commonly used it may be said to include everything from annealing to tempering. The proper use would seem to be confined to such heating and quenching as so changes the quality of the steel as to make it more suitable for its purpose. To properly heat-treat steel we must know its composition and at what degrees the critical changes occur. Steels for treatment should be classified into two distinct groups. In the first group are the alloy steels; those that carry certain percentages of manganese, chromium, nickel, vanadium or other elements. The purpose of heat treatment for the alloy group is to increase strength and toughness of material and at the same time to increase machining ability by leaving steel ductile. The second group includes the hardening and tempering of crucible steels. Heat treating includes annealing, case-hardening and the relieving of strains from hardening or forging operations. From text books we know that iron possesses the allotropic property of existing in three different conditions and still remain the same chemically. If we heat pure iron to 1,390°F. it suddenly loses its magnetism, and instead of being soft and ductile it becomes hard and brittle. If we continue to heat it until it reaches 1,635°F. it again suddenly changes its properties and instead of being brittle becomes again ductile, but still hard and non-magnetic. These stages of iron are called, respectively: Alpha Iron: Soft and ductile and stable below lower critical point. Beta Iron: Hard and brittle, stable between critical points. Gamma Iron: Hard and ductile and stable above high critical point. Now if carbon is added to the iron, the critical point is lowered in direct proportion to percentage of carbon, until point of calescense is reached, which in high-carbon steels is about 1,350°F Composition of Steel. — The composition of steel is given by Professor Sauveur, as follows: 105 106 THE WORKING OF STEEL First. — Ferrite, which is pure iron, low in tensile strength, but very soft and ductile. Second. — Cementite, which is a carbide of iron, present in steel over 0.90 carbon, very hard and brittle. Third. — Pearlite, which is simply a mechanical mixture of pure iron with cementite. Pearlite is present in steel in increasing percentage up to 0.90 carbon, with a corresponding decrease of ferrite. At 0.90 carbon the steel is all pearlite. When carbon is over 0.90 the pearlite decreases in percentage with a corresponding increase of per- centage of cementite. Every condition of heat on steels, from low critical point to that above high critical or overheated steel, has been recorded by numerous authors on the subject. DIFFERENT STEEL STRUCTURES We will touch on them briefly, not because of any actual value to the operator, but simply to show that a difference of a few degrees in heating gives a different structure of steel, easily recognizable under a microphotograph. Osmondite appears at about 750°F. when cementite begins to dissolve in Alpha iron. Sorbite appears at 1,100°F. and is nearly all pearlite but with a certain percentage of cementite undissolved. Pearlite is thoroughly saturated Alpha iron with cementite. Troostite is the higher carbon steels in tempered conditions. Martensite is properly hardened steel. Austentite is present in high-carbon overheated steel. Now to determine the transformations in both hardening and tempering alloy steel, the question will naturally arise as to the need of first hardening such steels and then tempering until it becomes ductile. The reason is that as steel solidifies after pouring it cools very rapidly from liquid state, thereby causing segregation (ferrite and cementite do not have time to combine), strains, etc. In reheating we bring it beyond the upper critical point to Gamma iron, that state wherein the condition is stable. Quenched from this temperature the molecules remain in the right crystallic form so that a slow tempering process can finish the work and deliver a perfect sorbitic or pearlitic saturation, as we may desire. HEAT TREATMENT OF STEEL 107 The Controlling Factors. — The factors which determine treat- ment are: Carbon is the controlling factor as to determining the critical point. In other words, the hardening temperature is determined by carbon contents. Manganese of 1 per cent or more controls the time of soaking at high critical point. High silicon will shorten time of soaking somewhat, but low silicon will not increase it. Chromium of more than 5 points will add 1°F. for each point of chromium to hardening heat as predetermined by carbon. For instance, if predetermined heat is 1,500°F. and steel to be hardened contains 1 per cent or 100 points chromium, add 100°F., making critical point 1,600°. Nickel of more than 10 points will add approximately one minute to soaking time for each point present up to 50 points; over 50 points both hardening and tempering heats will change. For tempering, a different process is carried out for determina- tion of factors. Carbon is practically eliminated as no martensite condition exists at heat of 700°F. and over. Manganese has done its real work keeping a sort of fibrous grip on the molecules in suspense. Silicon, in conjunction with sulphur and phosphorus, acts as lubricants and facilitates the relocation of saturated mass, from rigidity to one of ease. Too much of these elements will prevent the proper binding of molecules together and weakens structure, but all three are a great help for machining operations. Silicon should not exceed 0.30, sulphur not over 0.07, and phosphorus not over 0.09 per cent. Chrome and nickel when present control both temperature and time, in direct proportion to its percentage. When chromium is present at 1 per cent or more and nickel at 3 per cent or more, singly or combined, it becomes a problem not yet solved, to treat with any certainty of uniformity as far as ease of machining operations are concerned. THE DIFFERENT ELEMENTS The different elements in ordinary alloy steels have the follow- ing functions : 108 THE WORKING OF STEEL Carbon, for hardness and rigidity. Manganese, for toughness. Silicon, a sort of adjuster. Sulphur and phosphorus, as lubricants. Chromium, as a refiner of grain and to add hardness to help carbon. Nickel, as a protecting support of structure and aid to stability. Vanadium, in small doses, acts as a scavenger, in high percentage it helps to resist friction. Tungsten, to add keen cutting qualities and when present in sufficient quantity to resist heat. In the heat treating of alloy steel you have certain factors to bear in mind. These factors may vary slightly as to duration of heat and time limits, but they are always present. First. — You must know critical points. Second. — You must not fall below high critical point when soaking steel. Third. — Steel of same analysis must be subjected to same heat and same length of time for soaking to give uniform results. Fourth. — Quenching must be done in both within certain limits of tem- perature, depending on quality of work performed. Fifth. — Tempering heats range on 10°F. basis. Heat must be established on quality of work desired. Sixth. — A low limit must be set as to time necessary for soaking at high heat. This heat must not fall below that wanted, while being soaked, or time must again begin when temperature is again reached. Too long soak- ing may cause a reaction, giving a dry steel, with a great drop in elastic strength. Seventh. — -When work is taken out of furnace for tempering or annealing purposes it must be thoroughly covered. No chance must be left to form air pockets. Air-cooled steel will often contain hard spots on surface and soft spots in interior. THE CRITICAL POINTS The point of calescence can be determined by pyrometer, by closely watching the needle. A thermo-couple or fire end should be inserted in the steel. Drill a hole in a piece of steel to take in end of thermo-couple. As the heat advances, the needle will follow until it reaches a point where it suddenly stops, wavers and then suddenly drops several degrees although heat is constantly advancing. Then the needle will again suddenly commence its upward swing. Where the needle stops and rests, is calescence or low critical point. Now reverse the operation. Heat beyond the critical point, shut off the fuel, and watch for the same phenomena. The needle will start to drop back, then suddenly stop and advance several HEAT TREATMENT OF STEEL 109 degrees, after which it again starts to drop and continues down the scale. This upper change is called the recalescence point. The Magnet Test. — The critical point can also be determined by an ordinary horse shoe magnet. Touch the steel with a magnet during the heating and when it reaches the temperature at which steel fails to attract the magnet, or in other words, loses its Fig. 43. — Finding hardening heats with a magnet. magnetism, the point of calescence or critical point has been reached. Figures 43 and 44 show how these are used in practice. The first (Fig. 43) shows the use of a permanent horse shoe magnet and the second (Fig. 44) an electro-magnet consisting of an iron rod with a coil or spool magnet at the outer end. In either case the magnet should not be allowed to become heated but should be applied quickly. Fig. 44. — Using electro-magnet to determine heat. The work is heated up slowly in the furnace and the magnet applied from time to time. The steel being heated will attract the magnet until the heat reaches the critical point. The mag- net is applied frequently and when the magnet is no longer attracted, the piece is at the lowest temperature at which it can be hardened properly. Quenching at this point will give a tool of satisfactory hardness. 110 THE WORKING OF STEEL JUDGING THE HEAT OF STEEL While the use of a pyrometer is of course the only way to have accurate knowledge as to the heat being used in either forging or hardening steels, a color chart will be of considerable assistance if carefully studied. These have been prepared by several of the steel companies as a guide, but it must be remem- bered that the colors and temperatures given are only approximate, and can be nothing else. Different kinds of steel should be heated to different tem- peratures. High-speed steel, for example, can be heated to a white heat, or about 2,200°F. which is No. 11 on the scale given. But when made up into twist drills, milling cutters and similar tools it should only be heated up to No. 10. With carbon steels a much lower temperature is necessary. They should not be heated above a bright red for forging, this being perhaps 1,650°F. and for hardening the temperature should not exceed 1,500°F. In general the hardening temperature lies between 1,400° and 1,500°F. It is extremely difficult to give very definite instructions, as experience with the particular kind of steel you are using is the only way to be sure of your results. It is well to remember, however, that the lowest heat at which the piece, will harden satisfactorily is the best heat for that piece and that it is always safer to have the heat a trifle too low than too high. Milling cutters or other tools which are light and fragile, or have many cuts in them, do not require as much heat for hardening as do solid pieces of the same kind and size. Always reheat steel after forging, do not try to temper at the same heat. It is also important to have the heating for hardening as uniform as possible. Overheating does not increase the hardness but it does make the steel more brittle. It is safer to take a chance with a low heat as in that case you can reharden, while with an overheat the piece is very likely to be spoiled. Always use enough hardening liquid to prevent its becoming too warm before the piece cools, but do not have it too cold when the piece is dipped into it. If water is used it should be pure and have a temperature of about 60°F. A leeway of 5° either way will do no harm. For tempering with oil use a fish oil or linseed oil instead of HEAT TREATMENT OF STEEL 111 fatty oils. Always keep the tool in motion in the hardening bath until it becomes fairly cool. Also avoid sharp limits between the hardened and unhardened portions. In the case of a lathe tool move the tool in and out of the liquid as well as with a circular bath. Otherwise cracks are very apt to develop at the point where the tool has left the hardening liquid. Tempering, or drawing the temper, relieves some of the stresses imposed by the sudden cooling of the piece and increases the elasticity, or ability to withstand shocks because it reduces its brittleness. It is always safer to select a steel which is harder than may be necessary and draw the temper lower than to select a softer steel and leave the temper harder. The first piece will be hard enough and much stronger while the second will be brittle and not satisfactory. HEAT TREATMENT OF GEAR BLANKS This section is based on a paper read before the American Gear Manufacturers' Association at White Sulphur Springs. W. Va., Apr. 18, 1918, and outlines the advantages of thoroughly annealed blanks to the subsequent machining and hardening operations, as well as an exposition of the structural changes undergone by a piece of steel in the heat-treating process. Great advancement has been made in the heat treating and hardening of gears. In this advancement the chemical and metallurgical laboratory have played no small part. During this time, however, the condition of the blanks as they come to the machine shop to be machined has not received its share of attention in the heat-treating department of many forge shops, and in many cases has been neglected or not considered by the machine shops themselves. This is especially true of shops using only the lower carbon steels. There are two distinct types of gears, both types having their champions, namely, carburized and heat-treated. The difference between the two in the matter of steel composition is entirely in the carbon content, the carbon never running higher than 25-point in the carburizing type, while in the heat-treated gears the carbon is seldom lower than 35-point. The difference in the final gear is the hardness. The carburized gear is file hard on the surface, with a soft, tough and ductile core to withstand shock, while the heat-treated gear has a surface that can be touched by a file with a core of the same hardness as the outer surface. 112 THE WORKING OF STEEL Annealing Work. — With the exception of several of the higher types of alloy steels, where the percentages of special elements run quite high, which causes a slight air-hardening action, the carburizing steels are soft enough for machining when air cooled from any temperature, including the finishing temperature at the hammer. This condition has led many drop-forge and manu- facturing concerns to consider annealing as an unnecessary opera- tion and expense. In many cases the drop forging has only been heated to a low temperature, often just until the piece showed color, to relieve the so-called hammer strains. While this has been only a compromise it has been better than no re- heating at all, although it has not properly refined the grain, which is necessary for good machining conditions. Before going into the effects of proper annealing temperatures for the most commonly used steels we will briefly consider the theory of heat treatment. Heat treatment, in the broad sense, is the thermal refinement of the structure of steel, and covers the four operations, namely, annealing, carburizing, hardening and drawing, or tempering as it is commonly called. All of these operations are based on the fact that in heating a piece of steel the structure undergoes a change at from one to three points on heating and a corresponding number of changes on cooling, these changes being caused by a molecular rearrangement of the carbon and iron. The points are known as "critical points" or "critical ranges" and vary in number according to the composition of the steel. These points on heating are often referred to as "decal- escent point," and on cooling as "recalescent point." Carbon exerts the greatest influence on the location of the critical points, with nickel and chromium coming next. A straight-carbon steel up to 35-point carbon has three critical points; from 35- to 89-point carbon two critical points are found and over 89-point carbon only one critical temperature is found. Each 1 per cent of nickel will lower the critical point 20°F., while each 1 per cent of chromium raises the point 10°F. Of the critical points those found on a rising temperature are higher than the corresponding points on a falling temperature. Rising tempera- tures are always considered in correctly heat treating a piece of steel. In order to produce the most complete rearrangement of the molecules of carbon and iron and therefore the greatest re- finement it is necessary to heat to a temperature slightly in excess of the highest critical point. HE A T TREA TMENT OF STEEL 113 Annealing is heating to a temperature slightly above the high- est critical point and cooling slowly either in the air or in the furnace. Annealing is done to accomplish two purposes: (1) to relieve mechanical strains and (2) to soften and produce a maximum refinement of grain. Process of Carburizing. — Carburizing imparts a shell of high- carbon content to a low-carbon steel. This produces what might be termed a "dual" steel, allowing for an outer shell which when hardened would withstand wear, and a soft ductile core to pro- duce ductility and withstand shock. The operation is carried out by packing the work to be carburized in boxes with a material rich in carbon and maintaining the box so charged at a tempera- ture in excess of the highest critical point for a length of time to produce the desired depth of carburized zone. Generally main- taining the temperature at 1,650 to 1,700°F. for 7 hi*, will pro- duce a carburized zone }^2 m - deep. Heating to a temperature slightly above the highest critical point and cooling suddenly in some quenching medium, such as water or oil hardens the steel. This treatment produces a maxi- mum refinement with the maximum strength. Drawing to a temperature below the highest critical point (the temperature being governed by the results required) relieves the hardening strains set up by quenching, as well as the reducing of the hardness and brittleness of hardened steel. As the maximum refinement of the grain size of a piece of steel takes place at a temperature at or slightly above the highest critical point, increasing temperatures over that point correspond- ingly increases the grain size. The grain size of a piece of steel is governed by the maximum temperature reached after passing- over the highest critical point or by the temperature at which the last mechanical working was given the steel, providing the mechanical work was done at a temperature in excess of the highest critical point. Annealed steels are called pearlitic, "pearlite" being the name applied to the microstructure of slowly cooled steels. Pearlite is a mechanical mixture consisting of alternate masses in ferrite (pure iron) and cementite (cementite being a compound made up of 6.6 per cent carbon and 93.4 per cent ferrite) with the resultant mixture containing 0.89 per cent carbon. Pearlite may be pres- ent in two forms, lamellar and granular, with the granular occur- ring either coarse or fine or elongated with bands of ferrite separating the elongated grains of pearlite. 114 THE WORKING OF STEEL When etched in a weak alcoholic solution of picric or nitric acid and examined under the microscope the ferrite, untouched by the etching solution, appears white, while the pearlite shows up black. Effect of Proper Annealing. — Proper annealing of low-carbon steels causes a complete solution or combination to take place between the ferrite and pearlite, producing a homogeneous mass of small grains of each, the grains of the pearlite being surrounded by grains of ferrite. A steel of this refinement will machine to good advantage, due to the fact that the cutting tool will at all times be in contact with metal of uniform composition and will not be alternately coming in contact with the soft ferrite con- stituent and the harder carbon particles. While the alternate bands of ferrite and pearlite are micro- scopically sized, it has been found that with a Gleason or Fellows gear-cutting machine that rough cutting can be traced to poorly annealed steels, having either a pronounced banded structure or a coarse granular structure. A study of the microphotographs of several of the widely used low-carbon steels in gear manufacture will show the condition of the structure direct from the drop hammer, the pronounced banded structure of ferrite and pearlite and the change produced by thorough annealing. Temperature for Annealing. — Theoretically, annealing should be accomplished at a temperature at just slightly above the critical point. However, in practice the temperature is raised to a higher point in order to allow for the solution of the carbon and iron to be produced more rapidly, as the time required to produce complete solution is reduced as the temperature increases past the critical point. Temperatures exceeding the critical point by over 100°F. should never be used on account of the enlargement of the grains of pearlite and ferrite. Microphotographs of a piece of steel annealed at temperatures increasing by 25°F. from a point below the critical point to the burning point show clearly the effects of temperature on the grain size. For annealing the simpler types of low-carbon steels the follow- ing temperatures have been found to produce uniform machining conditions on account of producing uniform fine-grain pearlite structure : 1.15 to 0.25 Per Cent Carbon, Straight Carbon Steel. — Heat to 1,650°F. Hold at this temperature until the work is uniform- ly heated; pull from the furnace and cool in air. HEAT TREATMENT OF STEEL 115 0.15 to 0.25 Per Cent Carbon, \y 2 Per Cent Nickel, Y 2 Per Cent Chromium Steel. — Heat to 1,600°F. Hold at this tempera- ture until the work is uniformly heated; pull from the furnace and cool in air. 0.15 to 0.25 Per Cent Carbon, 3% Per Cent Nickel Steel- Heat to 1,575°F. Hold at this temperature until the work is uniformly heated; pull from the furnace and cool in air. In the annealing of the higher types of chrome-nickel steel, with the nickel content running about 3 per cent and the chro- mium about 1 per cent the operation is more difficult, as rapid cooling through the upper critical range produces a hardness due to the slight air-hardening properties of steel of this composition. The annealing of this type of steel requires considerably more attention both in the heating and cooling. To produce the best machinability of this steel the following practice will give very satisfactory results : Heat to a temperature about 100°F., in excess of the critical point, holding at this temperature for a considerable time to allow for thorough heating and complete solution of the cementite; cool rapidly, either by pulling from the furnace into air or opening up the furnace doors to a point at which the forgings show no color in daylight; reheat to a point just in excess of the highest critical point and cool slowly in the furnace. The temperatures, length of heating, and time and rate of cooling are dependent on analysis, size of forging and weight of the load of forgings in the furnace. Care in Annealing. — Not only will benefits in machining be found by careful annealing of forgings but the subsequent troubles in the hardening plant will be greatly reduced. The advantages in the hardening start with the carburizing operation, as a steel of uniform and fine grain size will carburize more uniformly, pro- ducing a more even hardness and less chances for soft spots. The holes in the gears will also " close in more uniformly," not caus- ing some gears to require excessive grinding and others with just enough stock. Also all strains will have been removed from the forging, eliminating to a great extent distortion and the noisy gears which are the result. With the steels used for the heat-treated gears, always of a higher carbon content, treatment after forging is necessary for machining, as it would be impossible to get the required produc- tion from untreated forgings, especially in the alloy steels. The treatment is more delicate, due to the higher percentage of carbon 116 THE WORKING OF STEEL and the natural increase in cementite together with complex carbides which are present in some of the higher types of alloys. Due to the many analyses of heat-treated gear steer it is impos- sible to give in this paper specific treatments. More time should be given to permit complete solution to take place and the rate of cooling watched closely, together with the temperature at which the forgings are pulled from the fur- nace. For a furnace load weighing 550 lb. of medium-section steel forgings 0.50 per cent carbon, 0.60 per cent manganese, 3 per cent nickel, 1 per cent chromium the following treatment gave very good machining conditions on turning operations as well as on the Fellows gear-shaping machine: Heat to 1,330°F., taking 2 hr.to heat to the temperature. Hold at the temperature for 1% hr. and allow to cool in furnace to 1,170°F., taking about 1 hr. to cool. Reheat to 1,230°F., consuming % hr. to reheat. Hold at 1,230°F. for 134 hr. Cool slowly in furnace, not faster than 75° for the first hour, until 900°F., then cool in air. Where poor machining conditions in heat-treated steels are present they are generally due to incomplete solution of cementite rather than bands of free ferrite, as in the case of case-hardening steels. This segregation of carbon, as it is sometimes referred to, causes hard spots which, in the forming of the tooth, cause the cutter to ride over the hard metal, producing high spots on the face of the tooth, which are as detrimental to satisfactory gear cutting as the drops or low spots produced on the face of the teeth when the pearlite is coarse-grained or in a banded condition. In the simpler carburized steels it is not necessary to test the forgings for hardness after annealing, but with the high percent- ages of alloys in the carburizing steels and the heat-treated steels a hardness test is essential. For this test the Brinell hardness tester is far more accurate than the sclerescope test. However the Brinell test should not be used without the aid of the microscope. To obtain the best results in machining, the microstructure of the metal should be determined and a hardness range set that covers the variations in structure that produce good machin- ing results. By careful control of the heat-treating operation and with the aid of the Brinell hardness tester and the microscope it is possible to continually give forgings that will machine uniformly and be soft enough to give desired production. The HEAT TREATMENT OF STEEL 117 following gives a few of the hardness numerals on steel used in gear manufacture that produce good machining qualities: 20 per cent carbon, 3 per cent nickel, 134 per cent chromium — Brinell 156-170. 50 per cent carbon, 3 per cent nickel, 1 per cent chromium — Brinell 179-187. 50 per cent carbon chrome vanadium — Brinell 170-9. THE INFLUENCE OF SIZE The size of the piece influences the physical properties ob- tained in steel by heat treatment. This has been worked out by E. J. Jaintzky, metallurgical engineer of the Illinois Steel Company, as follows: _ 28 o 24 fc 20 V 16 l\ \\\ ■C^f 1 2 3 4 5 6 7 8 Diameter in Inches Fig. 45. — Effect of size on heating. "With an increase in the mass of steel there is a corresponding de- crease in both the minimum surface hardness and depth hardness, when quenched from the same temperature, under identical conditions of the quenching medium. In other words, the physical properties obtained are a function of the surface of the metal quenched for a given 118 THE WORKING OF STEEL mass of steel. Keeping this primary assumption in mind, it is possible to predict what physical properties may be developed in heat treating by calculating the surface per unit mass for different shapes and sizes. It may be pointed out that the figures and chart that follow are not results of actual tests, but are derived by calculation. They indicate the mathematical relation, which, based on the fact that the physical properties of steel are determined not alone by the rate which heat is lost per unit of surface, but by the rate which heat is lost per unit of weight in relation to the surface exposed for that unit. The unit of weight has for the different shaped bodies and their sizes a certain sur- face which determines their physical properties. "For example, the surface corresponding to 1 lb. of steel has been computed for spheres, rounds and flats. For the sphere with a unit weight of 1 lb. the portion is a cone with the apex at the center of the sphere and the base the curved surface of the sphere (surface exposed to quenching). For rounds, a unit weight of 1 lb. may be taken as a disk or cylinder, the base and top surfaces naturally do not enter into calcu- lation. For a flat, a prismatic or cylindrical volume may be taken to represent the unit weight. The surfaces that are considered in this instance are the top and base of the section, as these surfaces are the ones exposed to cooling." The results of the calculations are as follows : Table 20. — Sphere Surface per pound of steel Y 2 . 648 sq. in. 3.531 sq. in. 5.294 sq. in. 7 . 062 sq. in. 2 in 10 . 61 sq. in. XY = 21.185. Table 21. — Round Diameter of sphere X 8 in . . . 6 in . . . 4 in . . . 3 in... Diameter of round X 8.0 6.0 5.0 4.0 3.0 2.0 1.0 0.5 Surface per pound of steel Y 1 .765 sq. in. 2.354 sq. in. 2.829 sq. in. 3.531 sq. in. 4.708 sq. in. fh 7.062 sq. in. in 14 . 125 sq. in. in 28 . 25 sq. in. 0.25 in 56.5 sq. in. XY = 14.124. HEAT TREATMENT OF STEEL 119 Table 22.— Flat Thickness Surface per of flat pound of steel X Y 8.0 in 0.8828 sq. in. 6.0 in 1.177 sq. in. 5.0 in 1 . 412 sq. in. 4.0 in 1.765 sq. in. 3.0 in....! 2.345 sq. in. 2.0 in 3 . 531 sq. in. 1.0 in 7 . 062 sq. in. 0.5 in 14.124 sq. in. 0.25 in 28.248 sq. in. XY = 7.062. Having once determined the physical qualities of a certain speci- men, and found its position on the curve we have the means to predict the decrease of physical qualities on larger specimens which receive the same heat treatment. When the surfaces of the unit weight as outlined in the foregoing- tables are plotted as ordinates and the corresponding diameters as abscissae, the resulting curve is a hyperbola and follows the law XY = C. In making these calculations the radii or one-half of the thickness need only to be taken into consideration as the heat is conducted from the center of the body to the surface, following the shortest path. The equations for the different shapes are as follows : For flats XY = 7.062 For rounds XY = 14.124 For spheres 17 = 21.185 It will be noted that the constants increase in a ratio of 1, 2, and 3, and the three bodies in question will increase in hardness on being quenched in the same ratio, it being understood that the diameter of the sphere and round and thickness of the flat are equal. Relative to shape, it is interesting to note that rounds, squares, octagons and other three axial bodies, with two of their axes equal, have the same surface for the unit weight. For example : Size Length Surface Weight Surface for 1 lb. 2 in. Sq. 12 in. 96.0 sq. in. 13.60 lb. 7.06 sq. in. 2 in. Round 12 in. 75.4 sq. in. 10.68 lb. 7.06 sq. in. Although this discussion is at present based upon mathematical analysis, it is hoped that it will open up a new field of investigation in which but little work has been done, and may assist in settling the as yet unsolved question of the effect of size and shape in the heat treat- ment of steel. 120 THE WORKING OF STEEL Heat Treatment of Rifle Parts. — Some idea of the large number of parts in a rifle which must be heat-treated may be had from the accompanying list. This also gives the practice in both hardening and tempering. The information is, of course, equally applicable to other parts of a similar nature. t, , . f Harden in cyanide at 1,500°F. Bayonet catch < _ . . .. I Quench in oil. Bayonet nut washer and screw. { Blue in niter at 800°F. f Case-harden at 780°C, 2Y 2 hr. to 3 hr. ■o ,, J Quench in oil. 1 Pack, bone %. [ Pack, leather }/i. „ ., . f Harden, open fire at 145°F. Bolt stop spring. ( Temper ^ niter at ^^ B , , ( Case-harden at 750°C., 2}i hr. \ Quench in oil. Pack, bone }^, leather }^. t, , , . ■ [Harden in open at 1,450°F. Butt plate cap spring { ^^ ^ niter at 80()OF Butt plate screw, large { Case-harden at 750°C, 2% hr. t, . i . ii f Quench in oil. Pack, old bone }■£. Pack, Butt plate screw, small < , n , I new bone }$. ( Case-harden at 750°C, 2% hr. Cocking piece -j Quench in oil. I Pack, whole bone (new). r Harden in cyanide at 1,500°F. Safety lock plunger \ Quench in oil. { Dip in niter, 1 min. r Case harden at 750°C, 2Y 2 hr. Sear \ Quench in oil. I Pack. Bone %, leather J4- s • f Case-harden at 750°C, 2 hr. \ Quench in oil. C Case harden at 750°C, 23^ hr. Sleeve ' \ Quench in oil. I Pack in whole bone (new). Harden in open at 1,450°F. \ Temper in lead at 900°F r Case-harden at 750°C, 2\i hr. Trigger \ Quench in oil. I Pack. Bone %, leather 3^. f Case-harden at 750°C, 2%, hr. I Pack. Whole bone (new). „ -. . . . . ,. f Harden in cyanide at 1,500°F. Safety lock spindle \ ~. . ,. , . , , I Draw riveting end in lead. Guard. { Blue in niter at 800°F. HEAT TREATMENT OF STEEL 121 Guard screw, front and rear Lower band spring . Case harden at 750 C C, 2)4 hr. Quench in oil. Pol. head. j Blue in niter at 800°F. ( Pack. Old bone K, new leather J^. [Harden in open fire at 1,450°F. I Temper in lead at 900°F. , , . , f Harden in open fire at 1,450°F. Lower band swivel < „ . , , , nrir ,oT7> I Temper in lead at 900 F. r Harden in open fire at 1,450°F. Magazine spring \ Temper in niter at 800°F. I Correct over flame. r Case-harden at 750°C., 2Y 2 hr. Cut-off \ Quench in water. I Pack. Bone %, leather Y±. „ , „ . „ f Case-harden at 700°C, V/ 2 hr. Cut-off spindle < „ ,. I Quench in water. r Harden in cynide at 1,500°F. Cut-*off plunger \ Quench in oil. I Dip in niter, 1 min. .p. /Harden in cynide at 1,500 C F. ' ' J Quench in oil. „. , f Case-harden at 750°C, 2}4 hr. Ejector pm.. • \ Black. / Harden in open fire at 1,450°F. Extractor. . . . . ^ Temper in lead &t QQQ o Y . . . / Harden in open at 1,450°F. \ Temper in lead. (• Case-harden at 750°C , 2}i hr. Follower \ Quench in oil. I Pack. -whole bone (new). HEAT-TREATING EQUIPMENT AND METHODS FOR MASS PRODUCTION The heat-treating department of the Brown-Lipe-Chapin Company, Syracuse, N. Y., runs day and night, and besides handling all the hardening of tools, parts of jigs, fixtures, special machines and appliances, carburizes and heat-treats every month between 150,000 and 200,000 gears, pinions, crosses and other components entering into the construction of differentials for automobiles. The treatment of the steel really begins in the mill, where the steel is made to conform to a specific formula. On the arrival of the rough forgings at the Brown-Lipe-Chapin factory, the first of a long series of inspections begins. 122 THE WORKING OF STEEL Annealing Method. — Forgings which are too hard to machine are put in pots with a little charcoal to cause a reducing atmos- phere and to prevent scale. The covers are then luted on and the pots placed in the furnace. Carbon steel from 15 to 25 points is annealed at 1,600°F. Nickel steel of the same carbon and containing in addition 3^ per cent nickel is annealed at 1,450°F. When the pots are heated through, they are rolled to the yard and allowed to cool. This method of annealing gives the best hardness for quick machining. The requirements in the machine operations are very rigid and, in spite of great care and probably the finest equipment of special machines in the world, a small percentage of the product fails to pass inspection during or at the completion of the machine operations. These pieces, however, are not a loss, for they play an important part in the hardening process, indicating as they do the exact depth of penetration of the carburizing material and the condition of both case and core. Heat-treating Department. — The heat-treating department occupies an L-shaped building. The design is very practical, with the furnace and the floor on the same level so that there is no lifting of heavy pots. Fuel oil is used in all the furnaces and gives highly satisfactory results. The consumption of fuel oil is about 2 gal. per hour per furnace. The work is packed in the pots in a room at the entrance to the heat-treatment building. Before packing, each gear is stamped with a number which is a key to the records of the analysis and complete heat treatment of that particular gear. Should a question at any time arise regarding the treatment of a certain gear, all the necessary information is available if the number on the gear is legible. For instance, date of treatment, furnace, carburizing material, position of the pot in the furnace, position of gear in pot, temperature of furnace and duration of treatment are all tabulated and tiled for reference. After marking, all holes and parts which are to remain un- carburized are plugged or luted with a mixture of Kaolin and Mellville gravel clay, and the gear is packed in the carburizing material. Bohnite, a commercial carburizing compound is used exclusively at this plant. This does excellent work and is economical. Broadly speaking, the economy of a carburizing compound depends on its lightness. The space not occupied by work must be filled with compound; therefore, other things being HEAT TREATMENT OF STEEL 123 equal, a compound weighing 25 lb. would be worth more than twice as much as one weighing 60 lb. per cubic foot. It has been claimed that certain compounds can be used over and over again, but this is only true in a limited way, if good work is required. There is, of course, some carbon in the compound after the first use, but for first-class work, new compound must be used each time. The Packing Department. — In Fig. 46 is shown the packing pots where the work is packed. These are of malleable cast iron, with an internal vertical flange around the hole A. This fits in a bell on the end of the cast-iron pipe B, which is luted in position with fireclay before the packing begins. At C is shown Fig. 46. — Packing department and special pots. a pot ready for packing. The crown gears average 10 to 12 in. in diameter and weigh about 11 lb. each. When placed in the pots, they surround the central tube, which allows the heat to circulate. Each pot contains five gears. Two complete scrap gears are in each furnace (i.e., one which fails to pass machining inspection), and at the top of front pot, are two or more short segments of scrap gear, used as test pieces to gage depth. After filling the top with compound, the lid D is luted on. Ten pots are then placed in a furnace. It will be noted that the pots to the right are numbered 1, 2, 3, 4, indicating the position they are to occupy in the furnace. The cast-iron ball shown at E is small enough to drop through the pipe B, but will not pass through the hole A in the bottom of 124 THE WORKING OF STEEL the pot. It is used as a valve to plug the bottom of the pot to prevent the carburizing compound from dropping through when removing the carburized gears to the quenching bath. Without detracting from the high quality of the work, the metallurgist in this plant has succeeded in cutting out one entire operation and reducing the time in the hardening room by about 24 hr. Formerly, the work was carburized at about 1,700°F. for 9 hr. The pots were then run out into the yard and allowed to cool slowly. When cool, the work was taken out of the pots, reheated and quenched at 1,600°F. to refine the core. It was again reheated to 1,425°F. and quenched to refine the case. Finally, it was drawn to the proper temper. Short Method of Treatment.- — In the new method, the packed pots are run into the case-hardening furnaces, which are heated to 1,600°F. On the insertion of the cold pots, the temperature naturally falls. The amount of this fall is dependent upon a number of variables, but it averages nearly 500°F. as shown in the pyrometer chart, Fig. 51. The work and furnace must be brought to 1,600°F. within 2% hr.; otherwise, a longer time will be necessary to obtain the desired depth of case. On this work, the depth of case required is designated in thousandths, and on crown gears, the depth in 0.028 in. Having brought the work to a temperature of 1,600°F. the depth of case mentioned can be obtained in about 5}^ hr- by maintaining this temperature. As stated before, at the top of each pot are several test pieces consisting of a whole scrap gear and several sections. After the pots have been heated at 1,600°F. for about 5^ hr., they are removed, and a scrap-section test-piece is quenched direct from the pot in mineral oil at not more than 100°F. The end of a tooth of this is then ground and etched to ascertain the depth of case. As these test pieces are of exactly the same cross-section as the gears themselves, the carburizing action is similar. When the depth of case has been found from the etched test pieces to be satisfactory, the pots are removed. The iron ball then is dropped into the tube to seal the hole in the bottom of the pot; the cover and the tube are removed, and the gears quenched direct from the pot in mineral oil, which is kept at a temperature not higher than 100°F. The Effect. — The heating at 1,600°F. gives the first heat treat- ment which refines the core, which under the former high heat HEAT TREATMENT OF STEEL 125 (1,700°E) was rendered coarsely crystalline. All the gears, including the scrap gears, are quenched direct from the pot in this manner. The gears then go to the reheating furnaces, situated in front of a battery of Gleason quenching machines. These furnaces accommodate from 12 to 16 crown gears. The carbon-steel gears are heated in a reducing atmosphere to about 1,425°R (depending on the carbon content) placed in the dies in the Gleason quench- ing machine, and quenched between dies in mineral oil at less than 100°F. The test gear receives exactly the same treatment as the others and is then broken, giving a record of the condition of both case and core. Affinity of Nickel Steel for Carbon. — The carbon- and nickel- steel gears are carburized separately owing to the difference in time necessary for their carburization. Practically all printed information on the subject is to the effect that nickel steel takes longer to carburize than plain carbon steel. This is directly op- posed to the conditions found at this plant. For the same depth of case, other conditions being equal, a nickel-steel gear would require from 20 to 30 min. less than a low carbon-steel gear. From the quenching machines, the gears go to the sand-blast- ing machines, situated in the wing of the heat-treating building, where they are cleaned. From here they are taken to the testing department. The tests are simple and at the same time most thorough. Testing and Inspection of Heat Treatment. — The hard parts of the gear must be so hard that a new mill file does not bite in the least. Having passed this file test at several points, the gears go to the center-punch test. The inspector is equipped with a wooden trough secured to the top of the bench to support the gear, a number of center punches (made of %-in. hex-steel having points sharpened to an angle of 120 deg.) and a hammer weighing about 4 oz. With these simple tools, supplemented by his skill, the inspector can feel the depth and quality of the case and the condition of the core. The gears are each tested in this way at several points on the teeth and elsewhere, the scrap gear being also subjected to the test. Finally, the scrap gear is securely clamped in the straightening press shown in Fig. 47. With a 33^-lb. hammer and a suitable hollow-ended drift manipulated by one of Sandow's understudies, teeth are broken out of the scrap gear at various points. These give a record confirming 126 THE WORKING OF STEEL the center-punch tests, which, if the angle of the center punch is kept at 120 deg. and the weight of the hammer and blow are uni- form, is very accurate. After passing the center-punch test the ends of the teeth are peened lightly with a hammer. If they are too hard, small particles fly off. Such gears are drawn in oil at a temperature of from 300 to 350°F., depending on their hardness. Some builders prefer to have the extreme outer ends of the teeth drawn some- what lower than the rest. This drawing is done on gas-heated red-hot plates, as shown at A in Fig. 48. Fig. 47. — -Press for holding test gears for breaking Nickel steel, in addition to all the tests given to carbon steel, is subjected to a Brinell test. For each steel, the temperature and the period of treatment are specific. For some unknown reason, apparently like material with like treatment will, in iso- lated cases, not produce like results. It then remains for the treatment to be repeated or modified, but the results obtained during inspection form a valuable aid to the metallurgist in determining further treatment. HEAT TREATMENT OF STEEL 127 Temperature Recording and Regulation. — Each furnace is equipped with pyrometers, but the reading and recording of all temperatures are in the hands of one man, who occupies a room with an opening into the end of the hardening department. The opening is about 15 ft. above the floor level. On each side of it, easily legible from all of the furnaces, is a board with the numbers of the various furnaces, as shown in Figs. 49 and 50. Opposite each furnace number is a series of hooks whereon are hung metal numbers representing the pyrometer readings of the temperature in that particular furnace. Within the room, as shown in Fig. 50, the indicating instrument is to the right, and to the left is a switchboard to connect it with the thermo-couples Fig. 48. — Gas heated drawing plate for tooth ends. in the various furnaces. The boards shown to the right and the left swing into the room, which enables the attendant easily to change the numbers to conform to the pyrometer readings. Readings of the temperatures of the carburizing furnaces are taken and tabulated every ten minutes. These, numbered 1 to 10, are shown on the board to the right in Fig. 49. The card shown in Fig. 51 gives such a record. These records are filed away for possible future reference. The temperatures of the reheating furnaces, numbered from 11 to 26 and shown on the board to the left in Fig. 49, are taken every 5 min. Each furnace has a large metal sign on which is marked the temperature at which the furnace regulator is required to keep 128 THE WORKING OF STEEL HEAT TREATMENT OF STEEL 129 his heat. As soon as any variation from this is posted on the board outside the pyrometer room, the attendant sees it and adjusts the burners to compensate. Dies for Gleason Tempering Machines. — In Fig. 52 is shown a set of dies for the Gleason tempering machine. These accu- OBROWN-LIPE-CHAPIN COMPANY y-N . METALLURGICAL DEPT. ^ / .fcSSw no kf. DA Tt jJl 4//&T iO BUN. TE«P. /^4aRB.J.J X . /3 K**-* ZMJL DISTRIBUTION OF HEAT HOURS AS PER CLASSES n 2 3 4 s 6 7 S 9 10 II 12 13 14 15 16 Fig. 51. — Carburizing furnace record. rately made dies fit and hold the gear true during quenching, thus preventing distortion. Referring to Fig. 52, the die A has a surface B which fits the face of the teeth of the gear C. This surface is perforated by a large number of holes which permit the quenching oil to circulate freely. The die A is set in the upper end of the plunger 130 THE WORKING OF STEEL A of the tempering machine, shown in Fig. 53, a few inches above the surface of the quench- ing oil in the tank TV. Inside the die A are the centering jaws D, Fig. 54, which are an easy fit for the bore of the gear C. The inner surface of the centering jaws is in the shape of a female cone. The upper die is shown at E. In the center (separate from it, but a snug sliding fit in it) is the expander G, which, during quenching, enters the taper in the centering jaws D, expand- ing them against the bore of the gear C. The faces F of the upper die E fit two angles at the back of the gear and are grooved for the passage of the quenching oil. The upper die E is secured to the die carrier B, shown in Fig. 9, and inside the die is the ex- pander G, which is backed up by compression springs. Hardening Operation. — Hardening a gear is accom- plished as follows : The gear is taken from the furnace by the furnaceman and placed in the lower die, surround- ing the centering jaws, as shown at H in Fig. 52 and C in Fig. 53. Air is then turned into the cylinder D, and the piston rod E, the die carrier B, the top die F and the expander G descend. The pilot H enters a hole in the center of HEAT TREATMENT OF STEEL 131 -80 to 90 lb. Air Pressure the lower die, and the expander G enters the centering jaws I, causing them to expand and center the gear C in the lower die. On further advance of the piston rod E, the ex- pander G is forced up- ward against the pres- sure of the springs J and the upper die F comes in contact with the upper surface of the gear. Further down- ward movement of the dies, which now clamp the work securely, over- comes the resistance of the pressure weight K (which normally keeps up the plunger A), and the gear is submerged in the oil. The quenching oil is circulated through a cooling system outside the building and enters the tempering machine through the inlet pipe L. When the machine is in the position shown, the oil passes out through the ports M in the lower plunger to the outer re- servoir N, passing to the cooling system by way of the overflow 0. When the lower plunger A is forced downward, the ports M are automatic- ally closed and the cool quenching oil from the inlet pipe L, having no other means of escape, passes through the holes in the lower die and the grooves the upper, circulat- ing in contact with the surfaces of the gear and passes to '///MM WWW///////W//WM -Gleason tempering machine. 132 THE WORKING OF STEEL the overflow. When the air pressure is released, the counter- weights return the parts to the positions shown in Fig. 53, and the operator removes the gear. The gear comes out uniformly hard all over and of the same degree of hardness as when tempered in an open tank. The output of the machine depends on the amount of metal to be cooled, but will average from 8 to 16 per hour. Each machine is served by one man, two furnaces being required to heat the work. A slight excess of oil is used in the firing of the furnaces to give a reducing atmosphere and to avoid scale. Fig. 54. — Hardening and shrinking sleeves. Carburizing Low-carbon Sleeves. — Low-carbon sleeves are carburized and pushed on malleable-iron differential-case hubs. Formerly, these sleeves were given two treatments after carburi- zation in order to refine the case and the core, and then sent to the grinding department, where they were ground to a push fit for the hubs. After this they were pushed on the hubs. By the method now employed, the first treatment refines the core, and on the second treatment, the sleeves are pushed on the hub and at the same time hardened. This method cuts out the internal grinding time, pressing on hubs, and haulage from one department to another. Also, less work is lost through splitting of the sleeves. HEAT TREATMENT OF STEEL 133 The machine for pushing the sleeves on is shown in Fig. 54. At A is the stem on which the hot sleeve B is to be pushed. The carburized sleeves are heated in an automatic furnace, which takes them cold at the back and feeds them through to the front, by which time they are at the correct temperature. The loose mandrel C is provided with a spigot on the lower end, which fits the hole in the differential-case hub. The upper end is tapered as shown and acts as a pilot for the ram D. The action of pushing on and quenching is similar to the action of the Gleason tempering machine, with the exception that water instead of oil is used as a quenching medium. The speed of operation depends on a number of variables, but from 350 to 500 can be heated and pressed on in 11 hr. Cyanide Bath for Tool Steels. — All high-carbon tool steels are heated in a cyanide bath. With this bath, the heat can be controlled within 3 deg. The steel is evenly heated without exposure to the air, resulting in work which is not warped and on which there is no scale. The cyanide bath is, of course, not available for high-speed steel because of the very high temperatures necessary. DROP FORGING DIES The kind of steel used in the die of course influences the heat treatment it is to receive, but this also depends on the kind of work the die is to perform. If the die is for a forging which is machined all over and does not have to be especially close to size, where a variation of 3^16 m - is n °t considered excessive, a low grade steel will be perfectly satisfactory. In cases of fine work, however, where the variation cannot be over 0.005 to 0.01 in. we must use a fine steel and prevent its going out of shape in the heating and quenching. A high quality crucible steel is suggested with about the following analysis: Carbon 0.75 per cent, manganese 0.25 per cent, silicon 0.15 per cent, sulphur 0.015 per cent, and phosphorus 0.015 per cent. Such a steel will have a decalescent point in the neighborhood of 1,355°F. and for the size used, probably in a die of approximately 8 in., it will harden around 1,450°F. To secure best results care must be taken at every step. The block should be heated slowly to about 1,400°F., the furnace closed tight and allowed to cool slowly in the furnace itself. It should not soak at the high temperature. 134 THE WORKING OF STEEL After machining, and before it is put in the furnace for hard- ening, it should be slowly preheated to 800 or 900°F. This can be done in several ways, some putting the die block in front of the open door of a hardening furnace and keeping the furnace at about 1,000°F. The main thing is to heat the die block very slowly and evenly. The hardening heat should be very slow, 7 hr. being none too long for such a block, bringing the die up gradually to the quench- ing temperature of 1,450°. This should be held for Y^ hr. or even a little more, when the die can be taken out and quenched. There should be no guess work about the heating, a good pyro- meter being the only safe way of knowing the correct temperature. The quenching tank should be of good size and have a spray or stream of water coming up near the surface. Dip the die block about 3 in. deep and let the stream of water get at the face so as to play on the forms. By leaving the rest of the die out of the water, moving the die up and down a trifle to prevent a crack at the line of immersion, the back of the block is left tough while the face is very hard. To overcome the tendency to warp the face it is a good plan to pour a little water on the back of the die as this tends to even up the cooling. The depth to which the die is dipped can be easily regulated by placing bars across the tank at the proper depth. After the scleroscope shows the die to be properly hardened, which means from 98 to 101, the temper should be drawn as soon as convenient. A lead pot in which the back of the die can be suspended so as to heat the back side, makes a good method. Or the die block can be placed back to the open door of a furnace. On a die of this size it may take several hours to draw it to the desired temper. This can be tested while warm by the sclero- scope method, bearing in mind that the reading will not be the same as when cold. If the test shows from 76 to 78 while warm, the hardness when cold will be about 83, which is about right for this work. S. A. E. HEAT TREATMENTS The Society of Automotive Engineers have adopted certain heat treatments to suit different steels and varying conditions. These have already been referred to on pages 39 to 41 in connection with the different steels used in automobile practice. These treatments are designated by letter and correspond with the designations in the table. HEAT TREATMENT OF STEEL 135 Heat Treatments Heat Treatment A After forging or machining : 1. Carbonize at a temperature be- 2. Gool slowly or quench. tween 1,600°F. and 1,750°F. 3. Reheat to 1,450-1,500°F. and (1,650-1,700°F. desired.) quench. Heat Treatment B After forging or machining : 1. Carbonize between 1,600°F. 4. Quench. and 1,750°F. (1,650-1,700°F. 5. Reheat to 1,400-1,450°F. desired.) 6. Quench. 2. Cool slowly in the carbonizing 7. Draw in hot oil at 300 to 450°F., mixture. depending upon the degree of 3. Reheat to 1, 550-1, 625°F. hardness desired. Heat Treatment D After forging or machining : 1. Heat to 1,500-1,600°F. 4. Quench. 2. Quench. 5. Reheat to 600-1, 200°F. and cool 3. Reheat to 1,450-1,500°F. slowly. Heat Treatment E After forging or machining : 1. Heat to 1, 500-1, 550°F. 4. Quench. 2. Cool slowly. 5. Reheat to 600-1, 200°F. and cool 3. Reheat to 1,450-1, 500°F. slowly. Heat Treatment F Af ter shaping or coiling : 1. Heat to 1,425-1,475°F. 3. Reheat to 400-900°F., in accord- 2. Quench in oil. ance with temper desired and cool slowly. Heat Treatment G After forging or machining : 1. Carbonize at a temperature between 1,600°F. and 1,750°F. (1,650- 1,700°F. desired). 2. Cool slowly in the carbonizing mixture. 3. Reheat to 1,500-1,550°F. 4. Quench. 5. Reheat to 1,300-1,400°F. 6. Quench. 7. Reheat to 250-500°F. (in accordance with the necessities of the case) and cool slowly. . Heat Treatment H After forging or machining : 1. Heat to 1,500-1,600°F. 2. Quench. 3. Reheat to 600-1, 200°F. and cool slowly. 136 THE WORKING OF STEEL Heat Treatment K After forging or machining: 1. Heat to 1,500-1, 550°F. 4. Quench. 2. Quench. 5. Reheat to 600-l,200°F. and cool 3. Reheat to 1, 300-1, 400°F. slowly. Heat Treatment L After forging or machining: 3. Reheat to 1,400-1, 500 0, F. 1. Carbonize between 1,600°F. 4. Quench. and 1,750°F. (1,650-1,700°F. 5. Reheat to 1,300-1,400°F. desired). 6. Quench. 2. Cool slowly in the carbonizing 7. Reheat to 250-500°F. and cool mixture. slowly. Heat Treatment M After forging or machining : 1. Heat to 1, 450-1, 500°F. 3. Reheat to 500-l,250°F. and cool 2. Quench. slowly. Heat Treatment P After forging or machining : 1. Heat to 1,450-1, 500°F. 4. Quench. 2. Quench. 5. Reheat to 500-l,250°F. and cool 3. Reheat to 1,375-1,450°F. slowly. Heat Treatment Q After forging : 3. Machine. 1. Heat to 1,475-1,525°F. (Hold 4. Reheat to 1,375-1,425°F. at this temperature one-half 5. Quench. hour, to insure thorough 6. Reheat to 250-550°F. and cool heating.) slowly. 2. Cool slowly. Heat Treatment R After forging : 4. Cool slowly. 1. Heat to 1,500-1,550°F. 5. Machine. 2. Quench in oil. 6. Reheat to 1,350-1,450°F. 3. Reheat to 1,200-1,300°F. (Hold 7. Quench in oil. at this temperature three 8. Reheat to 250-500°F. and cool hours.) slowly. Heat Treatment S After forging or machining: 3. Reheat to 1, 650-1, 750°F. 1. Carbonize at a temperature be- 4. Quench. tween 1,600 and 1,750°F. 5. Reheat to 1,475-1, 550°F. (1,650-1,700°F. desired.) 6. Quench. 2. Cool slowly in the carbonizing 7. Reheat to 250-550°F. and cool mixture. slowly. Heat Treatment T After forging or machining: 1. Heat to 1,650-1,750°F. 3. Reheat to 500-1, 300°F. and cool 2. Quench. slowly. HEAT TREATMENT OF STEEL 137 Heat Treatment U After forging : 3. Machine. 1. Heat to 1,525-1,600°F. (Hold 4. Reheat to 1, 650-1, 700°F. for about one-half hour.) 5. Quench. 2. Cool slowly. 6. Reheat to 350-550°F. and cool slowly. Heat Treatment V After forging or machining : 1. Heat to 1, 650-1, 750°F. 3. Reheat to 400-1, 200°F. and cool 2. Quench. slowly. RESTORING OVERHEATED STEEL The effect of heat treatment on overheated steel is shown graphically in Fig. 55 to the series of illustrations on pages 137 " \. / ;*» : *>'*>. V,i» l'«Sv. Visible in full daylighl 540 Full purple 560 Full blue 600 Very dark blue 752 Red heat, visible in the dark 885 Red heat, visible in the twilight 975 Red heat, visible in the daylight 1,292 Dark red 1,652 Cherry-red 1,832 Bright cherry-red 2,012 Orange-red 2,192 Orange-yellow 2,372 Yellow-white 2,552 White welding heat 2,732 Brilliant white 2,912 Dazzling white (bluish-white) 164 THE WORKING OF STEEL These differences might easily be due to the difference in the light at the time the colors were observed. It must also be remembered that even a thin coating of oil will make quite a difference and cause confusion. It is these possible sources of error, coupled with the ever present chance of human error, that makes it advisable to draw the temper of tools in an oil bath heated to the proper temperature as shown by an accurate high-temperature thermometer. Another table, by Gilbert and Barker, runs to much higher tem- peratures. Beyond 2,200°, however, the eye is very uncertain. Table 26. — Colors for Tempering Tools Approximate color and temperature Kind of tool Yellow 430 to 450°F. Thread chasers, hollow mills (solid type) twist drills, centering tools, forming tools, cut-off tools, profile cut- ters, milling cutters, reamers, dies, etc. Straw-yellow 460°F. Thread rolling dies, counterbores, countersinks, shear blades, boring tools, engraving tools, etc. Brown-yellow 500°F. Taps, Thread dies, cutters, reamers, etc. Light purple 530°F. Taps, dies, rock drills, knives, punches, gages, etc. Dark purple 550°F. Circular saws for metal, augers, dental and surgical in- struments, cold chisels, axes. Pale blue 580°F. Bone saws, chisels, needles, cutters, etc. Blue 600°F. Hack saws, wood saws, springs, etc. CHAPTER X HIGH-SPEED STEEL For centuries the secret art of making tool steel was handed down from father to son. The manufacture of tool steel is still an art which, by the aid of science, has lost much of its secrecy; yet tool steel is today made by practical men skilled as melters, hammer-men, and rollers, each knowing his art. These prac- tical men willingly accept guidance from the chemist and metallurgists. A knowledge of conditions existing today in the manufacture of high-speed steel is essential to steel treaters. It is well for the manufacturer to have steel treaters understand some of his troubles and difficulties, so that they will better comprehend the necessity of certain trade customs and practices, and, realiz- ing the manufacturer's desire to cooperate with them, will reciprocate. The manufacturer of high-speed steel knows and appreciates the troubles and difficulties that may sometimes arise in the heat-treating of his product. His aim is to make a uniform steel that will best meet the requirements of the average machine shop on general work, and at the same time allow the widest variation in heat treatment to give desired results. High speed steel is one of the most complex alloys known. A representative steel contains approximately 24 per cent of alloy- ing metals, namely, tungsten, chromium, vanadium, silicon, manganese, and in addition there is often found cobalt, molyb- denum, uranium, nickel, tin, copper and arsenic. STANDARD ANALYSIS The selection of a standard analysis by the manufacturer is the result of a series of compromises between various proper- ties imparted to the steel by the addition of different elements and there is a wide range of chemical analyses of various brands. The steel, to be within the range of generally accepted analysis, should contain over 16 per cent and under 20 per cent tungsten; 165 166 THE WORKING OF STEEL if of lower tungsten content it should carry proportionately more chromium and vanadium. The combined action of tungsten and chromium in steel gives to it the remarkable property of maintaining its cutting edge at relatively high temperature. This property is commonly spoken of as "red-hardness." The percentages of tungsten and chro- mium present should bear a definite relationship to each other. Chromiumim parts to steel a hardening property similar to that given by carbon, although to less a degree. The hardness im- parted to steel by chromium is accompanied by brittleness. The chromium content should be between 3.5 and 5 per cent. Vanadium was first introduced in high-speed steel as a "scaven- ger," thereby producing a more homogeneous product, of greater density and physical strength. It soon became evident that vanadium used in larger quantities than necessary as a scavenger imparted to the steel a much greater cutting efficiency. Recently, no less an authority than Prof. J. 0. Arnold, of the University of Sheffield, England, stated that "high-speed steels containing vanadium have a mean efficiency of 108.9, as against a mean efficiency of 61.9 obtained from those without vanadium content." A wide range of vanadium content in steel, from 0.5 to 1.5 per cent, is permissible. An ideal analysis for high-speed steel containing 18 per cent tungsten is a chromium content of approximately 3.85 per cent; vanadium, 0.85 to 1.10 per cent, and carbon, between 0.62 and 0.77 per cent. Detrimental Elements. — Sulphur and phosphorus are two elements known to be detrimental to all steels. Sulphur causes "red-shortness" and phosphorus causes "cold-shortness." The detrimental effects of these two elements counteract each other to some extent but the content should be not over 0.02 sulphur and 0.025 phosphorus. The serious detrimental effect of small quantities of sulphur and phosphorus is due to their not being uniformly distributed, owing to their tendency to segregate. The manganese and silicon contents are relatively unimportant in the percentages usually found in high-speed steel. The detrimental effects of tin, copper and arsenic are not generally realized by the trade. Small quantities of these impurities are exceedingly harmful. These elements are very seldom determined in customers' chemical laboratories and it is somewhat difficult for public chemists to analyze for them. HARDENING CARBON STEEL FOR TOOLS 167 In justice to the manufacturer, attention should be called to the variations in chemical analyses among the best of laboratories. Generally speaking, a steel works' laboratory will obtain results more nearly true and accurate than is possible with a customer's laboratory, or by a public chemist. This can reasonably be expected, for the steel works' chemist is a specialist, analyzing the same material for the same elements day in and day out. The importance of the chemical laboratory to a tool-steel plant cannot be over-estimated. Every heat of steel is analyzed for each element, and check analyses obtained; also, every substance used in the mix is analyzed for all impurities. The importance of using pure base materials is known to all manu- facturers despite chemical evidence that certain detrimental elements are removed in the process of manufacture. The manufacture of high-speed steel represents the highest art in the making of steel by tool-steel practice. Some may say, on account of our increased knowledge of chemistry and metal- lurgy, that the making of such steel has ceased to be an art, but has become a science. It is, in fact an art; aided by science. The human element in its manufacture is a decided factor, as will be brought in the following remarks: The heat treatment of steel in its broad aspect may be said to commence with the melting furnace and end with the harden- ing and tempering of the finished product. High-speed steel is melted by two general types of furnace, known as crucible and electric. Steel treaters, however, are more vitally interested in the changes that take place in the steel during the various processes of manufacture rather than a detailed description of those processes, which are more or less familiar to all. In order that good high-speed steel may be furnished in finished bars, it must be of correct chemical analysis, properly melted and cast into solid ingots, free from blow-holes and surface defects. Sudden changes of temperature are to be guarded against at every stage of its manufacture and subsequent treatment. The ingots are relatively weak, and the tendency to crack due to cooling strains is great. For this reason the hot ingots are not allowed to cool quickly, but are placed in furnaces which are of about the same temperature and are allowed to cool gradually before being placed in stock. Good steel can be made only from good ingots. Steel treaters should be more vitally interested in the impor- 168 THE WORKING OF STEEL tant changes which take place in high-speed steel during the hammering operations than that of any other working the steel receives in the course of its manufacture. QUALITY AND STRUCTURE The quality of high-speed steel is dependent to a very great extent upon its structure. The making of the structure begins under the hammer, and the beneficial effects produced in this stage persist through the subsequent operations, provided they are properly carried out. The massive carbides and tungstides present in the ingot are broken down and uniformily distributed throughout the billet. To accomplish this the reduction in area must be sufficient and the hammer blows should be heavy, so as to carry the compres- sion into the center of the billet; otherwise, undesirable character- istics such as coarse structure and carbide envelopes will exist and cause the steel treater much trouble. Surface defects invisible in the ingot may be opened up under the hammering operation, in which event they are chipped from the hot billet. Ingots are first hammered into billets. These billets are carefully inspected and all surface defects ground or chipped. The hammered billets are again slowly heated and receive a second hammering, known as "cogging." The billet resulting therefrom is known as a " cogged" billet and is of the proper size for the rolling mill or for the finishing hammer. Although it is not considered good mill practice, some manu- facturers who have a large rolling mill perform the very impor- tant cogging operation in the rolling mill instead of under the hammer. Cogging in a rolling mill does not break up and dis- tribute the carbides and tungstides as efficiently as cogging under the hammer; another objection to cogging in the rolling mill is that there is no opportunity to chip surface defects de- veloped as they can be under the trained eye of a hammer-man, thereby eliminating such defects in the finished billet. The rolling of high-speed steel is an art known to very few. The various factors governing the proper rolling are so numerous that it is necessary for each individual rolling mill to work out a practice that gives the best results upon the particular analysis of steel it makes. Important elements entering into the rolling HARDENING CARBON STEEL FOR TOOLS 169 are the heating and finishing temperatures, draft, and speed of the mill. In all of these the element of time must be considered. High-speed steel should be delivered from the rolling mill to the annealing department free from scale, for scale promotes the formation of a decarbonized surface. In preparation of bars for annealing, they are packed in tubes with a mixture of charcoal, lime, and other material. : The tubes are sealed and placed in the annealing furnace and the temperature is gradually raised to about 1,650°F., and held there for a sufficient length of time, depending upon the size of the bars. After very slow cooling the bars are removed from the tubes. They should then show a Brinnell number of between 235 and 275. The inspection department ranks with the chemical and metal- lurgical departments in safeguarding the quality of the product. It inspects all finished material from the standpoint of surface defects, hardness, size and fracture. It rejects such steel as is judged not to meet the manufacturer's standard. The inspection and metallurgical departments work hand in hand, and if any department is not functioning properly it will soon become evi- dent to the inspectors, enabling the management to remedy the trouble. The successful manufacture of high-speed steel can only be obtained by those companies who have become specialists. The art and skill necessary in the successful working of such steel can be attained only by a man of natural ability in his chosen trade, and trained under the supervision of experts. To become an expert operator in any department of its manufacture, it is necessary that the operator work almost exclusively in the pro- duction of such steel. As to the heat treatment, it is customary for the manufacturer to recommend to the user a procedure that will give to his steel a high degree of cutting efficiency. The recommendations of the manufacturer should be conservative, embracing fairly wide limits, as the tendency of the user is to adhere very closely to the manufacturer's recommendations. Unless one of the manufacturer's expert service men has made a detailed study of the customer's problem, the manufacturer is not justified in laying down set rules, for if the customer does a little experiment- ing he can probably modify the practice so as to produce results that are particularly well adapted to his line of work. The purpose of heat-treating is to produce a tool that will 170 THE WORKING OF STEEL cut so as to give maximum productive efficiency. This cutting efficiency depends upon the thermal stability of the complex hardenites existing in the hardened and tempered steel. The writer finds it extremely difficult to convey the meaning of the word "hardenite" to those that do not have a clear conception of the term. The complex hardenites in high-speed steel may be described as that form of solid solution which gives to it its cutting efficiency. The complex hardenites are produced by heat- ing the steel to a very high temperature, near the melting point, which throws into solution carbides and tungstides, provided they have been properly broken up in the hammering process and uniformly distributed throughout the steel. By quenching the steel at correct temperature this solid solution is retained at atmospheric temperature. It is not the intention to make any definite recommendations as to heat-treating of high-speed steel by the users. It is recog- nized that such steel can be heat-treated to give satisfactory results by different methods. It is, however, believed that the American practice of hardening and tempering is becoming more uniform. This is due largely to the exchange of opinions in meetings and elsewhere. The trend of American practice for hardening is toward the following: First, slowly and carefully preheat the tool to a temperature of approximately 1,500°F., taking care to prevent the formation of excessive scale. Second, transfer to a furnace, the temperature of which is approximately 2,250 to 2,400°F., and allow to remain in the furnace until the tool is heated uniformly to the above temperature. Third, cool rapidly in oil, dry air blast, or lead bath. Fourth, draw back to a temperature to meet the physical requirements of the tool, and allow to cool in air. It was not very long ago that the desirability of drawing hardened high-speed steel to a temperature of 1,100° was pointed out, and it is indeed encouraging to learn that comparatively few treaters have failed to make use of this fact. Many treaters at first contended that the steel would be soft after drawing to this temperature and it is only recently, since numerous actual tests have demonstrated its value, that the old prejudice has been eliminated. High-speed steel should be delivered only in the annealed HARDENING CARBON STEEL FOR TOOLS 171 condition because annealing relieves the internal strains inevi- table in the manufacture and puts it in vastly improved physical condition. The manufacturer's inspection after annealing also discloses defects not visible in the unannealed state. The only true test for a brand of high-speed steel is the service that it gives by continued performance month in and month out under actual shop conditions. The average buyer is not justified in conducting a test, but can well continue to purchase his requirements from a reputable manufacturer of a brand that is nationally known. The manufacturer is always willing to cooperate with the trade in the conducting of a test and is much interested in the information received from a well con- ducted test. A test, to be valuable, should be conducted in a manner as nearly approaching actual working conditions in the plant in which the test is made as is practical. In conducting a test a few reputable brands should be allowed to enter. All tools entered should be of exactly the same size and shape. There is much difference of opinion as to the best practical method of conducting a test, and the decision as to how the test should be conducted should be left to the customer, who should cooperate with the manufacturers in devising a test which would give the best basis for conclusions as to how the particular brands would perform under actual shop conditions. The value of the file test depends upon the quality of the file and the intelligence and experience of the person using it. The file test is not reliable, but in the hands of an experienced oper- ator, gives some valuable information. Almost every steel treater knows of numerous instances where a lathe tool which could be touched with a file has shown wonderful results as to cutting efficiency. Modern tool-steel practice has changed from that of the past, not by the use of labor-saving machinery, but by the use of scientific devices which aid and guide the skilled craftsman in producing a steel of higher quality and greater uniformity. It is upon the intelligence, experience, and skill of the individual that quality of tool steel depends. HARDENING HIGH-SPEED STEELS We will now take up the matter of hardening high-speed steels. The most ordinary tools used are for lathes and planers. The 172 THE WORKING OF STEEL forging should be done at carbon-steel heat. Rough-grind while still hot and preheat to about carbon-steel hardening heat, then heat quickly in high-speed furnace to white heat, and quench in oil. If a very hard substance is to be cut, the point of tool may be quenched in kerosene or water and when nearly black, finish cooling in oil. Tempering must be done to suit the material to be cut. For cutting cast iron, brass castings, or hard steel, tempering should be done merely to take strains out of steel. On ordinary machinery steel or nickel steel the temper can be drawn to a dark blue or up to 900°F. If the tool is of a special form or character, the risk of melting or scaling the point cannot be taken. In these cases the tool should be packed, but if there is no packing equipment, a tool can be heated to as high heat as is safe without risk to cutting edges, and cyanide or prussiate of potash can be sprinkled over the face and then quenched in oil. Some very adverse criticism may be heard on this point, but experience has proved that such tools will stand up very nicely and be perfectly free from scales or pipes. Where packing can- not be done, milling cutters, and tools to be hardened all over, can be placed in muffled furnace, brought to 2,220° and quenched in oil. All such tools, however, must be preheated slowly to 1,400 to 1,500° then placed in a high-speed furnace and brought up quickly. Do not soak high-speed steel at high heats. Quench in oil. We must bear in mind that the heating furnace is likely to expand tools, therefore provision must be made to leave extra stock to take care of such expansion. Tools with shanks such as counter bores, taps, reamers, drills, etc., should be heated no further than they are wanted hard, and quench in oil. If a forge is not at hand and heating must be done, use a muffle furnace and cover small shanks with a paste from fire clay or ground asbestos. Hollow mills, spring threading dies, and large cutting tools with small shanks should have the holes thoroughly packed or covered with asbestos cement as far as they are wanted soft. CUTTING-OFF STEEL FROM BAR To cut a piece from an annealed bar, cut off with a hack saw, milling cutter or circular saw. Cut clear through the bar ; do not nick or break. To cut a piece from an unannealed bar, cut right off with an abrasive saw; do not nick or break. If of large cross- HARDENING CARBON STEEL FOR TOOLS 173 section, cut off hot with a chisel by first slowly and uniformly heating the bar, at the point to be cut, to a good lemon heat, 1,800 to 1,850°F. and cut right off while hot; do not nick or break. Allow the tool length and bar to cool before reheating for forging. LATHE AND PLANER TOOLS Forging. — Gently warm the steel to remove any chill, is par- ticularly desirable in the winter, then heat slowly and carefully to a scaling heat, that is a lemon heat (1,800 to2,000°F.), and forge uniformly. Reheat the tool for further forging directly the steel begins to stiffen under the hammer. Under no circumstances forge the steel when the temperature falls below a dark lemon to an orange color about 1,700°F. Reheat as often as is necessary to finish forging the tool to shape. Allow the tool to cool after forging by burying the tool in dry ashes or lime. Do not place on the damp ground or in a draught of air. The heating for forging should be done preferably in a pipe or muffle furnace but if this is not convenient use a good clean fire with plenty of fuel between the blast pipe and the tool. Never allow the tool to soak after the desired forging heat has been reached. Do not heat the tool further back than is necessary to shape the tool, but give the tool sufficient heat. See that the back of the tool is flatly dressed to provide proper support under the nose of the tool. Hardening High-speed Steel. — Slowy reheat the cutting edge of the tool to a cherry red, 1,400°F., then force the blast so as to raise the temperature quickly to a full white heat, 2,200 to 2,250°F., that is, until the tool starts to sweat at the cutting face. Cool the point of the tool in a dry air blast or preferably in oil,- further cool in oil keeping the tool moving until the tool has become black hot. To remove hardening strains reheat the tool to from 500 to 1,10'0°F. Cool in oil or atmosphere. This second heat treat- ment adds to the toughness of the tool and therefore to its life. Grinding Tools. — Grind tools to remove all scale. Use a quick-cutting, dry, abrasive wheel. If using a wet wheel, be sure to use plenty of water. Do not under any circumstances force the tool against the wheel so as to draw the color, as this is likely to set up checks on the surface of the tool to its detriment. 174 . THE WORKING OF STEEL FOR MILLING CUTTERS AND FORMED TOOLS Forging — Forge as before. — Annealing. — Place the steel in a pipe, box or muffle. Arrange the steel so as to allow at least 1 in. of packing, consisting of dry powder ashes, powdered charcoal, mica, etc., between the pieces and the walls of the box or pipe. If using a pipe close the ends. Heat slowly and uniformly to a cherry red, 1,375 to 1,450°F. according to size. Hold the steel at this temperature until the heat has thoroughly saturated through the metal, then allow the muffle box and tools to cool very slowly in a dying furnace or remove the muffle with its charge and bury in hot ashes or lime. The slower the cooling the softer the steel. The heating requires from 2 to 10 hr. depending upon the size of the piece. Hardening and Tempering. — It is preferable to use two fur- naces when hardening milling cutters and special shape tools. One furnace should be maintained at a uniform temperature from 1,375 to 1,450°F. while the other should be maintained at about 2,250°F. Keep the tool to be hardened in the low temperature furnace until the tool has attained the full heat of this furnace. A short time should be allowed so as to be assured that the center of the tool is as hot as the outside. Then quickly remove the tool from this preheating furnace to the full heat furnace. Keep the tool in this furnace only as long as is necessary for the tool to attain the full temperature of this furnace. Then quickly remove and quench in oil or in a dry air blast. Remove before the tool is entirely cold and draw the temper in an oil bath by raising the temperature of the oil to from 500 to 750°F. and allow this tool to remain, at this temperature, in the bath for at least 30 min., •insuring uniformity of temper; then cool in the bath, atmosphere or oil. If higher drawing temperatures are desired than those possible with oil, a salt bath can be used. A very excellent bath is made by mixing two parts by weight of crude potassium nitrate and three parts crude sodium nitrate. These will melt at about 450°F. and can be used up to 1,000°F. Before heating the steel in the salt bath, slowly preheat, preferably in oil. Reheating the hardened high-speed steel to 1,000°F. will materially increase the life of lathe tools, but milling and form cutters, taps, dies, etc., should not be reheated higher than 500 to 650°F., unless extreme HARDENING CARBON STEEL FOR TOOLS 175 hardness is required, when 1,100 to 1,000°F., will give the hardest edge. INSTRUCTIONS FOR WORKING HIGH-SPEED STEEL Owing to the wide variations in the composition of high-speed steels by various makers, it is always advisable to follow the directions of each when using his brand of steel. In the absence of specific directions the following general suggestions from several makers will be found helpful. The Ludlum Steel Company recommend the following : Cutting-off. — To cut a piece from an annealed bar, cut off with a hack saw, milling cutter or circular saw. Cut clear through the bar; do not nick or break. To cut a piece from an unannealed bar, cut right off with an abrasive saw; do not nick or break. If of large cross-section, cut off hot with a chisel by first slowly and uniformly heating the bar, at the point to be cut, to a good lemon heat, 1800°-1850°F. and cut right off while hot; do not nick or break. Allow the tool length and bar to cool before reheating for forging. LATHE AND PLANER TOOLS To Forge.— Gently w T arm the steel to remove any chill, is particularly desirable in the winter, then heat slowly and care- fully to a scaling heat, that is a lemon heat (1800°-2000°F.), and forge uniformly. Reheat the tool for further forging directly the steel begins to stiffen under the hammer. Under no cir- cumstances forge the steel when the temperature falls below a dark lemon to an orange color about 1700°F. Reheat as often as is necessary to finish forging the tool to shape. Allow the tool to cool after forging by burying the tool in dry ashes or lime. Do not place on the damp ground or in a draught of air. The heating for forging should be done preferably in a pipe or muffle furnace but if this is not convenient use a good clean fire with plenty of fuel between the blast pipe and the tool. Never allow the tool to soak after the desired forging heat has been reached. Do not heat the tool further back than is ne- cessary to shape the tool, but give the tool sufficient heat. See that the back of the tool is flatly dressed to provide proper support under the nose of the tool. 176 THE WORKING OF STEEL Hardening. — Slowly reheat the cutting edge of the tool to a cherry red, 1400°F., then force the blast so as to raise the tem- perature quickly to a full white heat, 2200°-2250°F., that is, until the tool starts to sweat at the cutting face. Cool the point of the tool in a dry air blast or preferably in oil, further cool in oil keeping the tool moving until the tool has become black hot. To remove hardening strains reheat the tool to from 500° to 1100°F. Cool in oil or atmosphere. This second heat treat- ment adds to the toughness of the tool and therefore to its life. Grinding. — Grind tools to remove all scale. Use a quick cutting, dry, abrasive wheel. If using a wet wheel, be sure to use plenty of water. Do not under any circumstances force the tool against the wheel so as to draw the color, as this is likely to set up checks on the surface of the tool to its detriment. The Firth-Sterling Steel Company say: Instead of printing any rules on the hardening and temper- ing of Firth-Sterling Steels we wish to say to our customers : Trust the steel to the skill and the judgement of your Tool- smith and Tool Temperer. The steel workers of today know by personal experience and by inheritance all the standard rules and theories on forging, hardening and tempering of all fine tool steels. They know the importance of slow, uniform heating, and the danger of overheating some steels, and under- heating others. The tempering of tools and dies is a science taught by heat, muscle and brains. The tool temperer is the man to hold responsible for results. The tempering of tools has been his life work. He may find suggestions on the following pages interesting, but we are always ready to trust the treatment of our steels to the experienced man at the fire. HEAT TREATMENT OF LATHE, PLANER AND SIMILAR TOOLS Fire. — For these tools a good fire is one made of hard foundry coke, broken in small pieces, in an ordinary blacksmith forge with a few bricks laid over the top to form a hollow fire. The bricks should be thor- oughly heated before tools are heated. Hard coal may be used very successfully in place of hard coke and will give a higher heat. It is very easy to give Blue Chip the proper heat if care is used in making up the fire. Forging. — Heat slowly and uniformly to a good forging heat. Do not hammer the steel after it cools below a bright red. Avoid as much as HARDENING CARBON STEEL FOR TOOLS 177 possible heating the body of the tool, so as to retain the natural tough- ness in the neck of the tool. Hardening. — Heat the point of the tool to an extreme white heat (about 2,200°F.) until the flux runs. This heat should be the highest possible short of melting the point. Care should be taken to confine the heat as near to the point as possible so as to leave the annealing and consequent toughness in the neck of the tool and where the tool is held in the tool post. Cool in an air blast, the open air or in oil, depending upon the tools or the work thej' are to do. For roughing tools temper need not be drawn except for work where the edge tends to crumble on account of being too hard. For finishing tools draw the temper to suit the purpose for which they are to be used. Grind thoroughly on dry wheel (or wet wheel if care is used to pre- vent checking). HEAT TREATMENT OF MILLING CUTTERS, DRILLS, REAMERS, ETC. The Fire. — Gas and electric furnaces designed for high heats are now made for treating high-speed steels. We recommend them for treating all kinds of Blue Chip tools and particularly the above class. After tools reach a yellow heat in the forge fire they must not be allowed to touch the fuel or come in contact with the blast or surrounding air. Heating. — Tools of this kind should be heated to a mellow white heat, or as hot as possible without injuring the cutting edges (2,000 to 2,200°F.). For most work the higher the heat the better the tool. Where furnaces are used, we recommend preheating the tools to a red heat in one furnace before putting them in a white hot furnace. Cooling. — We recommend quenching all of the above tools in oil when taken from the fire. We have found fish oil, cottonseed oil, Houghton's No. 2 soluble oil and linseed oil satisfactory. The high heat is the important thing in hardening Blue Chip tools. If a white hot tool is allowed to cool in the open air it will be hard, but the air scales the tool. Drawing the Temper. — Tools of this class should be drawn consider- ably more than water-hardening steel for the same purpose. HEAT TREATMENT OF PUNCHES AND DIES, SHEARS, TAPS, ETC. Heating. — The degree to which tools of the above classes should be heated depends upon the shape, size and use for which they are in- tended. Generally, they should not be heated to quite as high a heat 12 178 THE WORKING OF STEEL as lathe tools or milling cutters. They should have a high heat, but not enough to make the flux run on the steel (by pyrometer 1,900 to 2,100°F.). Cooling. — Depending on the tools, some should be dipped in oil all over, some only part way, and others allowed to cool down in the air naturally, or under air blast. In cooling, the toughness is retained by allowing some parts to cool slowly and quenching parts that should be hard. Drawing the Temper. — As in cooling, some parts of these tools will require more drawing than others, but, on the whole, they must be drawn more than water hardening tools for the same purpose or to about 500°F. all over, so that a good file will just " touch" the cutting or working parts. Barium Chloride Process. — This is a process developed for treating certain classes of tools, such as taps, forming tools, etc. It is being successfully used in many large plants. Briefly the treatment is as follows : In this treatment the tools are first preheated to a red heat, but small tools may be immersed without preheating. The barium chloride bath is kept at a temperature of from 2,000 to 2,100°F., and tools are held in it long enough to reach the same temperature. They are then dipped in oil. The barium chloride which adheres to the tools is brushed off, leaving the tools as clean as before heating. A CHROMIUM-COBALT STEEL The Latrobe Steel Company make a high-speed steel without tungsten, its red-hardness properties depending on chromium and cobalt instead of tungsten. It is known as P. R. K-33 steel. It does not require the high temperature of the tungsten steels, hardening at 1,830 to 1,850°F. instead of 2,200° or even higher, as with the tungsten. This steel is forged at 1,900 to 2,000°F. and must not be worked at a lower temperature than 1,600°F. It requires soaking in the fire more than the tungsten steels. It can be normalized by heating slowly and thoroughly to 1,475°F., holding this for from 10 to 20 min. according to the size of the piece and cooling in the open air, protected from drafts. A peculiarity of this steel is that it becomes non-magnetic at or above 1,960°F. and the magnetic quality is not restored by cooling. Normalizing as above, however, restores the magnetic qualities. This enables the user to detect any tools which have been overheated, with a horseshoe magnet. HARDENING CARBON STEEL FOR TOOLS 179 It is sometimes advantageous to dip tools, before heating for hardening, in ordinary fuel or quenching oil. The oil leaves a thin film of carbon which tends to prevent decarbonization, giving a very hard surface. For other makes of high-speed steel used in lathe and planer tools the makers recommend that the tools be cut from the bar with a hack saw or else heated and cut with a chisel. The heating should be very slow until the steel reaches a red after which it can be heated more rapidly and should only be forged at a high heat. It can be forged at very high heats but care should be taken not to forge at a low heat. The heating should be uniform and penetrate clear to the center of the bar before forging is begun. Reheat as often as necessary to forge at the proper heat. After forging cool in lime before attempting to harden. Do not attempt to harden with the forging heat as was sometimes done with the carbon tools. For hardening forged tools, heat slowly up to a bright red and then rapidly until the point of the tool is almost at a melting heat. Cool in a blast of cold, dry air. For large sizes of steel, cool in linseed oil or in fish oil as is most convenient. If the tools are to be used for finishing cuts heat to a bright yellow and quench in oil. Grind for use on a sand wheel or grindstone in preference to an emery or an artificial abrasive wheel. For hardening milling and similar cutters, preheat to a bright red, place the cutter on a round bar of suitable size, and revolve it quickly over a very hot fire. Heat as high as possible without melting the points of the teeth and cool in a cold blast of dry air or in fish oil. Light fragile cutters, twist drills, taps and formed cutters may be heated almost white and then dipped in fish oil for hardening. Where possible it is better to give an even higher heat and cool in the blast of cold, dry air as previously recommended. SUGGESTIONS FOR HANDLING HIGH-SPEED STEELS The following suggestions for. handling high-speed steels are given by a maker whose steel is probably typical of a number of different makes, so that they will be found useful in other cases as well. These include hints as to forging as well as hardening, together with a list of "dont's" which are often 180 THE WORKING OF STEEL very useful. This applies to forging, hardening of lathe, slot- ting, planing and all similar tools. Fig. 74. — All-steel, % in. square, J^ X 1 in., and larger is usually mild finished, and can be cut in a hack saw. If cut off hot, be sure to heat the butt end slowly and thoroughly in a clean fire. Rapid and insufficient heating invariably cracks the steel. If you want to stamp the end with the name of the steel, it is necessary that this is done at a good high orange color heat, as it is otherwise apt to split the steel. (Take your time, do not hurry.) Hardening High-speed Steel In forging use coke for fuel in the forge. Heat steel slowly and thoroughly to a lemon heat. Do not forge at a lower heat. Do not let the steel cool Fig. 75. — Be sure to have a full yellow heat at the dotted line. Remember this is a boring mill tool and will stand out in the tool-post, and if you do not have a high thorough lemon heat, your tool will snap off at the dotted line. (Ninety-five per cent of all tools which break, have been forged at too low a heat or at a heat not thorough to the center.) below a bright cherry red while forging. After the tool is dressed, reheat to forging heat to remove the forging strain, and lay on the floor until cold. Then have the tool rough ground on a dry emery wheel. Fig. 76. — Keep your high lemon forging heat up. If you forge under a steam hammer, take light blows. Do not jam your tool into shape. Put frequently back into the fire. Never let the high lemon color go down and beyond the dotted line. For built-up and bent tools special care should be taken that the forging heat does not go below a bright cherry. For tools % by 1% or larger where HARDENING CARBON STEEL FOR TOOLS 181 there is a big strain in forging, such as bending at angles of about 45 deg. and building the tools up, they should be heated to at least 1,700°F. slowly and without much blast. For a % by 1%, tool it should take about 10 min. with the correct blast in a coke fire. Larger tools in proportion. They can Fig. 77. — Be sure that the tool is absolutely straight at the bottom, so as to lie flat in the tool-post. then be bent readily, but no attempt should be made to forge the steel further without reheating to maintain the bright cherry red. This is essen- tial, as otherwise the tools crack in hardening or while in use. Fig. 78. — This is the finished forged tool, and let this grow cold by itself, the slower the better. It is well to cool the tool slowly in hot ashes, to remove all forging strain. You can now grind the tool dry on a sharp emery wheel. The more you now finish the tool in grinding, the less there is to come off after hardening. In hardening place the tool in a coke fire (hollow fire if possible) with a slow blast and heat gradually up to a white welding heat on the nose of the tool. Then dip the white hot part only into thin oil or hold in a strong Fig. 79. — This tool is ground, ready for hardening. forging heat. Never harden from the cold' air blast. When hardening in oil do not hold the tool in one place but keep it moving so that it cools as quickly as possible. It is not neces- sary to draw the temper after hardening these tools. In grinding all tools should be ground as lightly as possible on a soft wet 182 THE WORKING OF STEEL Fig. 80. — Heat the nose of the tool only up to dotted line, very slowly and thoroughly to an absolutely white welding heat, so that it shows a trifle fused around the edges, and be very sure that this fusing has gone thoroughly through the nose, otherwise the fusing effect will be taken off after the second grinding. Note the difference of the nose between this and Fig. 79. Fig. 81. — Shows unnecessary roasting and drossing. Such hardening requires a great amount of grinding and is not good. After hardening grind carefully on a wet emery wheel, and be sure that the wheel is sharp with a plentiful supply of water. Do not force the grinding, otherwise the cold water striking the steel heated up by friction, will crack the nose. Be sure that the grinding wheel is sharp. | HARDENING CARBON STEEL FOR TOOLS 183' sandstone or on a wet emery wheel, and care should be taken not to create any surface cracks, which are invariably the result of grinding too forcibly. The following illustrations, Figs. 74 to 81, with their captions, will be found helpful. Special points of caution to be observed when hardening high-speed steel. Don't use a green coal fire; use coke, or build a hollow fire. Don't have the bed of the fire free from coal. Don't hurry the heating for forging. The heating has to be done very slowly and the forging heat has to be kept very high (a full lemon color) heat and the tool has to be continually brought back into the fire to keep the high heat up. When customers complain about seams and cracks, in 9 cases out of 10, this has been caused by too low a forging heat, and when the blacksmith complains about tools cracking, it is necessary to read this paragraph to him. Don't try to jam the tool into shape under a steam hammer with one or two blows; take easy blows and keep the heat high. Don't have the tool curved at the bottom; it must lie perfectly flat in the tool post. Don*t harden from your forging heat; let the tool grow cold or fairly cold. After forging you can rough grind the tool dry, but not too forcibly. Don't, for hardening, get more than the nose white hot. Don't get the white heat on the surface only. Don't hurry your heating for hardening; let the heat soak thoroughly through the nose of the tool. Don't melt the nose of the tool. Don't, as a rule, dip the nose into water; this should be done only for extremely hard material. It is dangerous to put the nose into water for fear of cracking and when you do put the nose into water put just J^ in. only of the extreme white hot part into the water and don't keep it too long in the water; just a few seconds, and then harben in oil. We do not recom- mend water hardening. Don't grind too forcibly. Don't grind dry after hardening. Don't discolor the steel in grinding. Don't give too much clearance on tools for cutting cast iron. Don't start on cast iron with a razor edge on the tool. Take an oil stone and wipe three or four times over the razor edge. Don't use tool holder steel from bars without hardening the nose of each individual tool bit. Air-hardening Steels. — These steels are recommended for boring, turning and planing where the cost of high-speed seems excessive. They are also recommended for hard wood knives, for roughing and finishing bronze and brass, and for hot bolt forging dies. This steel cannot be cut or punched cold but can be shaped and ground on abrasive wheels of various kinds. It should be heated slowly and evenly for forging and kept 184 THE WORKING OF STEEL as evenly heated at a bright red as possible. It should not be forged after it cools to a dark red. After the tool is made, heat it again to a bright red and lay it down to cool in a dry place or it can be cooled in a cold, dry air blast. Water must be kept away from it while it is hot. CHAPTER XI FURNACES There are so many standard furnaces now on the market that it is not necessary to go into details of their design and construc- Fig. 82. — Standard lead pot furnace. tion and only a few will be illustrated. Oil, gas and coal or coke are most common but there is a steady growth of the use of electric furnaces. 185 186 THE WORKING OF STEEL Typical Oil-fired Furnaces. — Several types of standard oil- fired furnaces are shown herewith. Figure 82 is a lead pot furnace, Fig. 83 is a vertical furnace with a center column. This column reduces the cubical contents to be heated and also supports the cover. Fig. 83.— Furnace with center column. A small tool furnace is shown in Fig. 84 which gives the con- struction and heat circulation. A larger furnace for high-speed steel is given in Fig. 85. The steel is supported above the heat, the lower flame passing beneath the support. For hardening broaches and long reamers and tops, the furnace shown in Fig. 86 is used. Twelve jets are used, these coming in radially to produce a whirling motion. FURNACES 187 Oil and gas furnaces may be divided into three types : the open heating chamber in which combustion takes place in the chamber and directly over the stock; the semimume heating chamber in B-<=£ =n Fig. 84. — Furnace for cutting tools. which combustion takes place beneath the floor of the chamber from which the hot gases pass into the chamber through suit- Fig. 85. — High-speed steel furnace. able openings; and the muffle heating chamber in which the heat entirely surrounds the chamber but does not enter it. The open furnace is used for forging, tool dressing and welding. The muffle furnace is used for hardening dies, taps, cutters and similar 188 THE WORKING OF STEEL tools of either carbon or high-speed steel. The muffle furnace is for spring hardening, enameling, assaying and work where the gases of combustion may have an injurious effect on the material. j" r H 3"* :•: ■■■ ■'■-: I ■■!; J.LJ " 2f 3 Y 3 3T ft FT ; ■; ^ *%A z V Fig. 86. — Furn'ace for hardening broaches. Furnaces of these types of oil-burning furnaces are shown in Figs. 87, 88 and 89; these being made by the Gilbert & Barker Manufacturing Company. The first has an air curtain formed FURNACES 189 ,i" fW ,: : v,,,,, ; . : t>- msm ' :< ^Hy 190 THE WORKING OF STEEL by jets from the large pipe just below the opening, to protect the operator from heat. Fig. 90. — Gas fired furnace. oft SECTIONAL FLAN LONGITUDtNAL SECTION CROSS SECTION Fig. 91. — Car door type of annealing furnace. Oil furnaces are also made for both high- and low-pressure air, each having its advocates. The same people also make gas- fired furnaces. Several types of furnaces for various purposes are illustrated FURNACES 191 in Figs. 90 and 91. The first is a gas-fired hardening furnace of the surface-combustion type. A large gas-fired annealing furnace of the Maxon system is shown in Fig. 91. This is large enough for a flat car to be run into as can be seen. It shows the arrangement of the burners, the track for the car and the way in which it fits into the furnace. These are from the designs of the Industrial Furnace Corporation. Before deciding upon the use of gas or oil, all sides of the problem should be considered. Gas is perhaps the nearest ideal but is as a rule more expensive. The tables compiled by the Gilbert & Barker Manufacturing Company and shown herewith, may help in deciding the question. Table 27. — Showing Comparison of Oil Fuel with Various Gaseous Fuels Heat units per thousand cubic feet Natural gas 1,000,000 Air gas (gas machine) 20 cp 815,500 Public illuminating gas, average 650,000 Water gas (from bituminous coal) •>.... 377,000 Water and producer gas, mixed 175,000 Producer gas 150,000 Since a gallon of fuel oil (7 lb.) contains 133,000 heat units, the following comparisons may evidently be made. At 5 cts. a gallon, the equivalent heat units in oil would equal: Per thousand cubic feet Natural gas at $0,375 Air gas, 20 cp at 0.307 Public illuminating gas, average at . 244 Water gas (from bituminous coal) at . 142 Water and producer gas, mixed at . 065 Producer gas at . 057 Comparing oil and coal is not always simple as it depends on the work to be done and the construction of the furnaces. The variation rises from 75 to 200 gal. of oil to a ton of coal. For forging and similar work it is probably safe to consider 100 gal. of oil as equivalent to a ton of coal. Then there is the saving of labor in handling both coal and ashes, the waiting for fires to come up, the banking of fires and the dirt and nuisance generally. The continuous operation possible with oil adds to the output. 192 THE WORKING OF STEEL When comparing oil and gas it is generally considered that 4^ gal. of fuel oil will give heat equivalent to 1,000 cu. ft. of coal gas. The pressure of oil and air used varies with the system in- stalled. The low-pressure system maintains a pressure of about 8 oz. on the oil and draws in free air for combustion. Others use a pressure of several pounds, while gas burners use an average of perhaps 1^ lb. of air to give best results. The weights and volumes of solid fuels are: Anthracite coal, 55 to 65 lb. per cubic feet or 34 to 41 cubic feet per ton; bitu- minous coal, 50 to 55 lb. per cubic feet or 41 to 45 cubic feet per ton; coke, 28 lb. per cubic feet or 80 cubic feet per ton — the ton being calculated as 2,240 lb. in each case. A novel carburizing furnace that is being used by a number of people, is built after the plan of a tireless cooker. The walls of the furnace are extra heavy, and the ports and flues are so arranged that when the load in the furnace and the furnace is thoroughly heated, the burners are shut off and all openings are tightly sealed. The carburization then goes on for several hours before the furnace is cooled below the effective carburizing range, securing an ideal diffusion of carbon between the case and the core of the steel being carburized. This is particularly adaptable where simple steel is used. PROTECTIVE SCREENS FOR FURNACES Workmen needlessly exposed to the flames, heat and glare from furnaces where high temperatures are maintained suffer in health as well as in bodily discomfort. This shows several types of shields designed for the maximum protection of the furnace worker. Bad conditions are not necessary; in almost every case means of relief can be found by one earnestly seeking them. The larger forge shops have adopted flame shields for the majority of their furnaces. Years ago the industrial furnaces (particularly of the oil-burning variety) were without shields, but the later models are all shield-equipped. These shields are adapted to all of the more modern, heat-treating furnaces, as well as to those fur- naces in use for working forges; and attention should be paid to their use on the former type since the heat-treating furnaces are constantly becoming more numerous as manufacturers find need of them in the many phases of munitions making or similar work. The heat that the worker about these furnaces must face may be divided in general into two classes : there is first that heat due to the flame and hot gases that the blast in the furnaces forces FURNACES 193 out onto a man's body and face. In the majority of furnaces this is by far the most discomforting, and care must be taken to fend it and turn it behind a suitable shield. The second class is the radiant heat, discharged as light from the glowing interior of the furnace. This is the lesser of the two evils so far as general forging furnaces are concerned, but it becomes the predominating feature in furnaces of large door area such as in the usual case- hardening furnaces. Here the amount of heat discharged is often almost unbearable even for a moment. This heat can be taken care of by interposing suitable, opaque shields that will temporarily absorb it without being destroyed by it, or becoming incandescent. Should such shields be so constructed as to close off all of the heat, it might be impossible to work around the furnace for the removal of its contents, but they can be made movable, and in such a manner as to shield the major portion of the worker's body. First taking up the question of flame shields, the illustration, Fig. 92, is a typical installation that shows the main features for application to a forging machine or drop-hammer, oil-burning furnace, or for an arched-over, coal furnace where the flame blows out the front. This shield consists of a frame covered with sheet metal and held by brackets about 6 in. in front of the furnace. It will be noted that slotted holes make this frame adjustable for height, and it should be lowered as far as possible when in use, so that the work may just pass under it and into the furnace openings. Immediately below the furnace openings, and close to the furnace frame will be noted a blast pipe carrying air from the forge-shop fan. This has a row of small holes drilled in its upper side for the entire length, and these direct a curtain of cold air vertically across the furnace openings, forcing all of the flame, or a greater portion of it, to rise behind the shield. Since the shield extends above the furnace top there is no escape for this flame until it has passed high enough to be of no further discomfort to the workman. In this case fan-blast air is used for cooling, and this is cheaper and more satisfactory because a great volume may be used. However, where high-pressure air is used for atomizing the oil at the burner, and nothing else is available, this may be employed — though naturally a comparatively small pipe will be needed, in which minute holes are drilled, else the volume of air used will 13 194 THE WORKING OF STEEL FURNACES 195 be too great for the compressor economically to supply. Steam may also be employed for like service. The latest shields of this type are all made double, as illus- trated, with an inner sheet of metal an inch or two inside of the front. In the illustration, A, Fig. 92, this inner sheet is smaller, but some are now built the same size as the front and bolted to it with pipe spacers between. The advantage of the double sheet is that the inner one bears the brunt of the flame, and, if needs be, burns up before the outer; while, if due to a heavy fire it should be heated red at any point, the outer sheet will still be much cooler and act as an additional shield to the furnace man. Heavy Forging Practice.— In heavy forging practice where the metal is being worked at a welding heat, the amount of flame that will issue from an open-front furnace is so great that a plain, sheet-steel front will neither afford sufficient protection nor stand up in service. For such a place a water-cooled front is often used. The general type of this front is illustrated in Fig. 93, and appears to have found considerable favor, for numbers of its kind are scattered throughout the country. In this case the shield is placed at a slight angle from the vertical, and along the top edge is a water pipe with a row of small holes through which sprays of water are thrown against it. This water runs down in a thin sheet over the shield, cooling it, and is collected in a trough connected with a run-off pipe at the bottom. The lower blast-pipe arrangement is similar to the one first described. There are several serious objections to this form of shield that should lead to its replacement by a better type; the first is that with a very hot fire, portions in the center may become so rapidly heated that the steam generated will part the sheet of water and cause it to flow from that point in an inverted V, and that section will then quickly become red hot. Another feature is that after the water and fire are shut down for the night the heat of the furnace can be great enough to cause serious warping of the surface of the shield so that the water will no longer cover it in a thin, uniform sheet. After rigging up a big furnace with a shield of this type several years ago, its most serious object was found in the increase of the water bill of the plant. This was already of large proportions, but it had suddenly jumped to the extent of several hundred 196 THE WORKING OF STEEL dollars. Investigation soon disclosed the fact that this water shield was one of the main causes of the added cost of water. A little estimating of the amount of water that can flow through a l^-in. pipe under 30-lb. pressure, in the course of a day, will show that this amount at 10 cts. per 1,000 gal., can count up rather rapidly. Figure 93 is a section through a portion of the furnace front and shield showing all of the principal parts. This shield consists essentially of a very thin tank, about 2}^ in. between walls, and filled with water. Like other shields it is fitted with an adjust- ment, that it may be raised and lowered as the work demands. The tank having an open top, the water as it absorbs heat from the flame will simply boil away in steam ; and only a small amount will have to be added to make up for that which has evaporated. The water-feed pipe shown at F ends a short distance above the top of the tank so that just how much water is running in may readily be seen. An overflow pipe is provided at which aids in maintaining the water at the proper height, as a sufficient quantity can al- ways be permitted to run in, to avoid any possibility of the shield ever boiling dry; at the same time the small excess can run off without danger of an overflow. The shield illustrated in Fig. 94 has been in constant use for over two years, giving greater satisfaction than any other of which the writer has known. It might also be noted that this shield was made with riveted joints, the shop not having a gas-welding outfit. To flange over the edges and then weld them with an acetylene torch would be a far more economical procedure, and would also insure a tight and permanent joint. The water-cooled front shown in Fig. 95 is an absurd effort to accomplish the design of a furnace that will provide cool working conditions. This front was on a bolt-heating furnace using hard coal for fuel; and it may be seen that it takes the place of all of the brickwork that should be on that side. Had this been noth- ing more than a very narrow water-cooled frame, with brickwork below and supporting bricks above, put in like the tuyeres in a foundry cupola, the case would have been somewhat different, for then it would have absorbed a smaller proportion of the heat. A blacksmith who knows how a piece of cold iron laid in a small welding furnace momentarily lowers the temperature, will appreciate the enormous amount of extra heat that must be maintained in the central portion of this furnace to make up FURNACES 197 for the constant chilling effect of the cold wall. Moreover, since there would have been serious trouble had steam generated in this front, a steady stream of water had to be run through it constantly to insure against an approach to the boiling point, This is illustrated because of its absurdity, and as a warning of something to avoid. Water-cooled, tuyere openings, as mentioned above, which support brick side-walls of the furnace, have proved successful for coal furnaces used for forging machine and drop-hammer heating, since they permit a great amount of work to be handled through their openings without wearing away as would a brick arch. Great care should be exercised properly to design them so that a minimum amount of the cold tuyere will be in contact with the interior of the furnace, and all interior portions possible should be covered by the bricks. However, a discussion of these points will hardly come in the flame-shield class, although they can be made to do a great deal toward relieving the excessive heat to be borne by the furnace worker. Flange Shields for Furnaces. — Such portable flame shields as the one illustrated in Fig. 96 may prove serviceable before furnaces required for plate work, where the doors are often only opened for a moment at a time. This shield can be placed far enough in front of the furnace, that it will be possible to work under it or around it, in removing bulky work from the furnace, and yet it will afford the furnace tender some relief from the excessive glare that will come out the wide-opened door. To have this shield of light weight so that it may be readily pushed aside when not wanted, the frame may be made up of pipe and fittings, and a piece of thin sheet steel fastened in the panel by rings about the frame. About the most disagreeable task in a heat-treating shop is the removal of the pots from the case-hardening furnaces; these must be handled at a bright red heat in order that their contents may be dumped into the quenching tank with a minimum- time contact with the air, and before they have cooled sufficiently to require reheating. Facing the heat before the large open doors of the majority of these furnaces, in a man-killing task even when the weather is moderately cool. The boxes soon become more or less distorted, and then even the best of lifting devices will not remove a hot pot without several minutes labor in front of the doors. In Fig. 97 is shown a method of arranging a shield on one 198 THE WORKING OF STEEL type of charging and removing truck. This shield cannot afford more than a partial protection to the body of the furnace tender, because he must be able to see around it, and in some cases even push it partly through the door of the furnace, but even small as it is it may still afford some welcome protection. The great advantage in this case of having the shield on the truck instead of stationary in front of the furnace, is that it still affords protection as long as the hot pot is being handled through the shop on its way to the quenching tank. It might be interesting to many engaged in the heat-treating or case hardening of steel parts, to make a special note of the design of the truck that is illustrated in connection with the shield; the general form is shown although the actual details for the construction of such a truck are lacking; these being simple, may be readily worked out by anyone wishing to build one. This is considered to be one of the quickest and easiest operated devices for the removal of this class of work from the furnace. To be sure it may only be used where the floor of the furnace has been built level with the floor of the room, but many of the modern furnaces of this class are so designed. The pack-hardening pots are cast with legs, from two to three inches high, to permit the circulation of the hot gases, and so heat more quickly. Between these legs and under the body of the pot, the two forward prongs of the truck are pushed, tilting the outer handle to make these prongs as low as possible. The handle is then lowered and, as it has a good leverage, the pot is easily raised from the floor, and the truck and its load rolled out. Heating of Manganese Steel. — Another form of heat-treating furnace is that which is used for the heating of manganese and other alloy steels, which after having been brought to the proper heat are drawn from the furnace into an immediate quenching tank. With manganese steel in particular, the parts are so fragile and easily damaged while hot that it is frequent practice to have a sloping platform immediately in front of the furnace door down which the castings may slide into a tank below the floor level. Such a furnace with a quenching tank in front of its door is shown in Fig. 98. These tanks are covered with plates while charging the furnace, and the cold castings are placed in a moderately cool furnace Since some of these steels must not be charged into a furnace where the heat is extreme but should be brought up to their FURNACES 199 final heat gradually, there is little discomfort during the charging process. When quenching, however, from a temperature of 1,800° to 1,900°, it is extremely unpleasant in front of the doors. The swinging shield is here adapted to give protecton for this work. As will be noted it is hung a sufficient distance in front of the doors, that it may not interfere with the castings as they come from the furnace, and slide down into the tank. To facilitate the work, and avoid the necessity of working with the bars outside the edges of the shield, the slot-like hole is cut in the center of the shield, and through this the bars or rakes for dragging out the castings are easily inserted and manipulated. The advantage of such a swinging shield is that it may be readily moved from side to side, or forward and back as occasion requires. FURNACE DATA In order to give definite information concerning furnaces, fuels etc., the following data is quoted from a paper by Seth A Moulton and W. H. Lyman before the Steel Heat Treaters Society in September, 1920. This considers a factory producing 30,000 lb. of automobile gears per 24 hr. The transmission gears will be of high-carbon steel and the differential of low-carbon steel, carburized. The heat-treating equipment required is: 1. Annealing furnaces 1,400 to 1,600°F. 2. Carburizing furnaces 1,700 to 1,800°F. 3. Hardening furnaces 1,450 to 1,550°F. 4. Drawing furnaces 350 to 950°F. All of the forging blanks are annealed before machining, about three-quarters of the machined gears and parts are carburized, all the carburized gears are given a double treatment for core and case, all gears and parts are hardened and all parts are drawn. The possible sources of heat supply and their values are as follows : — 1. Oil 140,000 B.t.u. per gallon 2. Natural gas 1,100 B.t.u. per cubic foot 3. City gas 650 B.t.u. per cubic foot 4. Water gas 300 B.t.u. per cubic foot 5. Producer gas 170 B.t.u. per cubic foot 6. Coal 12,000 B.t.u. per pound 7. Electric current 3,412 B.t.u. per kilowatt-hour 200 THE WORKING OF STEEL For the heat treatment specified only comparatively low temperatures are required. No difficulty will be experienced in attaining the desired maximum temperature of 1,800°F. with any of the heating medium above enumerated; but it should be noted that the producer gas with a B.t.u. content of 170 per cubic foot and the electric current would require specially designed fur- naces to obtain higher temperatures than 1800°F. Table 28. — Comparative Operating Costs Assuming Cost of oil- and gas-fired furnaces in- stalled as $100. 00 per square foot of hearth Cost of coal-fired furnace installed as . . 150 . 00 per square foot of hearth Cost of electric furnace 100 kw. capac- ity installed as 90 . 00 per kilowatt Cost of electric furnace 150 kw. capac- ity installed as 70 . 00 per kilowatt Output 3,000 lb. charge, 8 hr. heat carburizing, 2 hr. heating only. An- nual service 7,200 hr. Fixed charges including interest, depreciation, taxes, insurance and maintenance 15 per cent. Extra operating labor for coal- fired furnace 60 cts. per hour, one man four furnaces. Cost 3F Various Types ot< Furnaces Class fuel Fuel per charge Unit fuel cost Installa- tion cost Effi- ciency, per cent Fixed charges Cost per charge 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Oil 52.0 gal. 4.4 M 8.3 M 18.7 M 37.3 M 814.0 lb. 500.0 kw-hr. $0.15 gat. 0.50 M 0.80 M 0.40 0.10 M 6.00 ton 0.015kw. $2,400.00 2,400.00 2,400.00 2,400.00 2,400.00 3,600.00 9,000.00 12.6 18.8 17.0 16.4 14.5 9.4 53.0 $.40 0.40 0.40 0.40 0.40 0.60 1.50 $8.20 .5 °E u 03 O Natural gas. . . City gas Water gas Producer gas . . Coal Electricity 2.60 7.04 7.88 4.13 3.98 9.00 CD Oil Natural gas. . . City gas Water gas Producer gas . . Coal 30.8 gal. 2.61 M 4.9 M ' 11.1 M 22.1 M 348.0 1b. 329 . kw-hr. 0.15 gal. 0.50 M 0.80 M 0.40 M 0.10 M 6.00 ton 0.015kw. 2,400.00 2,400.00 2,400.00 2,400.00 2,400.00 3,600.00 10,500.00 21.4 32.0 28.8 27.6 24.6 22.0 81.75 0.10 0.10 0.10 0.10 0.10 0.15 0.44 4.72 1.40 4.02 4.54 2.31 1.38 Electricity 5.38 This shows but two of the operations and for a single furnace. The total costs for all operations on the 30,000 lb. of gears per 24 hr. is shown in Table 29. FURNACES 201 MMHrttiNHndHnNN K P O o O o - E- . i-' .-< in oo-(M oo h n Tf io ono -H 3 >, > ■+j +j y. xbb ££ FM CHAPTER XII PYROMETRY AND PYROMETERS A knowledge of the fundamental principles of pyrometry, or the meausrement of temperatures, is quite necessary for one engaged in the heat treatment of steel. It is only by careful measurement and control of the heating of steel that the full benefit of a heat-treating operation is secured. Before the advent of the thermo-couple, methods of tempera- ture measurement were very crude. The blacksmith depended on his eyes to tell him when the proper temperature was reached, and of course the "color " appeared different on light or dark days. "Cherry" to one man was "orange" to another, and it was therefore almost impossible to formulate any treatment which could be applied by several men to secure the same results. One of the early methods of measuring temperatures was the "iron ball" method. In this method, an iron ball, to which a wire was attached, was placed in the furnace and when it had reached the temperature of the furnace, it was quickly removed by means of the wire, and suspended in a can containing a known quantity of water; the volume of water being such that the heat would not cause it to boil. The rise in temperature of the water was measured by a thermometer, and, knowing the heat capacity of the iron ball and that of the water, the temperature of the ball, and therefore the furnace, could be calculated. Usually a set of tables was prepared to simplify the calculations . The iron ball , however, scaled, and changed in weight with repeated use, making the determinations less and less accurate. A copper ball was often used to decrease this change, but even that was subject to error. This method is still sometimes used, but for really precise work, a platinum ball, which will not scale or change in weight, is necessary, and the cost of this ball, together with the slowness of the method, have rendered the practice obsolete except for armor plate as has been described. PYROMETERS Armor plate makers still use the copper ball or Siemens' water pyrometer because they can place a number of the balls or 202 PYROMETRY AND PYROMETERS 203 weights on the plate in locations where it is difficult to use other pyrometers. One of these pyrometers is shown in section in Fig. 99. Siemens' Water Pyrometer. — It consists of a cjdindrical copper vessel provided with a handle and containing a second smaller copper vessel with double walls. An air space a separates the two vessels, and a layer of felt the two walls of the inner one, in order to retard the exchange of temperature with the surround- ings. The capacity of the inner vessel is a little more than one pint. A mercury thermometer b is fixed close to the wall of the inner vessel, its lower part being pro- tected by a perforated brass tube, whilst the upper projects above the vessel and is divided as usual on the stem into degrees, Fahrenheit or Centigrade, as desired. At the side of the thermometer there is a small brass scale c, which slides up and down, and on which the high temperatures are marked in the same degrees as those in which the mercury thermometer is divided ; on a level with the zero division of the brass scale a small pointer is fixed, which traverses the scale of the thermometer. Short cylinders d, of either copper, iron or platinum, are supplied with the pyro- meter, which are so adjusted that their heat capacity at ordinary temperature is equal to one-fiftieth of that of the copper vessel filled with one pint of water. As, however, the specific heat of metals in- creases with the temperature, allowance is made on the brass sliding scales, which are divided according to the metal used for the pyrometer cylinder d. It will therefore be understood that a different sliding scaleis required for the particu- lar kind of metal of which a cylinder is composed. In order to obtain accurate measurements, each sliding scale must be used only in conjunction with its own thermometer, and in case the latter breaks a new scale must be made and graduated for the new thermometer. The water pyrometer is used as follows: Fig. 99. — Siemens' copper- ball pyrometer. 204 THE WORKING OF STEEL Exactly one pint (0.568 liter) of clean water, perfectly distilled or rain water, is poured into the copper vessel, and the pyrometer is left for a few minutes to allow the thermometer to attain the temperature of the water. The brass scale c is then set with its pointer opposite the tem- perature of the water as shown by the thermometer. Meanwhile one of the metal cylinders has been exposed to the high tempera- ture which is to be measured, and after allowing sufficient time for it to acquire that temperature, it is rapidly removed and dropped into the pyrometer vessel without splashing any of the water out. The temperature of the water will rise until, after a little while, the mercury of the thermometer has become stationary. When this is observed the degrees of the thermometer are read off, as well as those on the brass scale c opposite the top of the mercury. The sum of these two values together gives the temperature of the flue, furnace or other heated space in which the metal cylinder had been placed. With cylinders of copper and iron, temperatures up to 1,800°F. (1000°C.) can be measured, but with platinum cylinders the limit is 2,700°F. (1,500°C). For ordinary furnace work either copper or wrought-iron cylinders may be used. Iron cylinders possess a higher melting- point and have less tendency to scale than those of copper, but the latter are much less affected by the corrosive action of the furnace gases; platinum is, of course, not subject to any of these disadvantages. The weight to which the different metal cylinders are adjusted is as follows: Copper 137.0 grams Wrought-iron 112.0 grams Platinum 402.6 grams In course of time the cylinders lose weight by scaling; but tables are provided giving multipliers for the diminished weights, by which the reading on the brass scale should be multiplied. THE THERMO-COUPLE With the application of the thermo-couple, the measurement of temperatures, between, say, 700 and 2,500°F., was made more simple and precise. The theory of the thermo-couple is simple; it is that if two bars, rods, or wires of different metals are joined PYROMETRY AND PYROMETERS 205 together at their ends, when heated so that one junction is hotter than the other, an electromotive force is set up through the metals, which will increase with the increase of the difference of temperature between the two junctions. This electromotive force, or voltage, may be measured, and, from a chart previously prepared, the temperature determined. In most pyrometers, of course, the temperatures are inscribed directly on the voltmeter, but the fact remains that it is the voltage of a small electric current, and not heat, that is actually measured. There are two common types of thermo-couples, the first mak- ing use of common, inexpensive metals, such as iron wire and nichrome wire. This is the so-called "base metal" couple. The other is composed of expensive metals such as platinum wire, and a wire of an alloy of platinum with 10 per cent of rhodium or iridium. This is called the "rare metal" couple, and because its component metals are less affected by heat, it lasts longer, and varies less than the base metal couple. The cold junction of a thermo-couple may be connected by means of copper wires to the voltmeter, although in some installa- tions of base metal couples, the wires forming the couple are themselves extended to the voltmeter, making copper connections unnecessary. From the foregoing, it may be seen that accurately to measure the temperature of the hot end of a thermo-couple, we must know the temperature of the cold end, as it is the difference in the temperatures that determines the voltmeter readings. This is absolutely essential for precision, and its importance cannot be over-emphasized. When pyrometers are used in daily operation, they should be checked or calibrated two or three times a month, or even every week. Where there are many in use, it is good practice to have a master pyrometer of a rare metal couple, which is used only for checking up the others. The master pyrometer, after calibrating against the melting points of various substances, will have a calibration chart which should be used in the checking operation. It is customary now to send a rare metal couple to the Bureau of Standards at Washington, where it is very carefully calibrated for a nominal charge, and returned with the voltmeter readings of a series of temperatures covering practically the whole range of the couple. This couple is then used only for checking those in daily use. Pyrometer couples are more or less expensive, and should be 206 THE WORKING OF STEEL cared for when in use. The wires of the couple should be insu- lated from each other by fireclay leads or tubes, and it is well to encase them in a fireclay, porcelain, or quartz tube to keep out the furnace gases, which in time destroy the hot junction. This tube of fireclay, or porcelain, etc., should be protected against breakage by an iron or nichrome tube, plugged or welded at the hot end. These simple precautions will prolong the life of a couple and maintain its precision longer. Sometimes erroneous temperatures are recorded because the "cold end" of the couple is too near the furnace and gets hot. This always causes a temperature reading lower than the actual, and should be guarded against. It is well to keep the cold end cool with water, a wet cloth, or by placing it where cool air will circulate around it. Best of all, is to have the cold junction in a box, together with a thermometer, so that its temperature may definitely be known. If this temperature should rise 20°F. on a hot day, a correction of 20°F. should be added to the pyrometer reading, and so on. In the most up-to-date installations, this cold junction compensation is taken care of automatically, a fact which indicates its importance. Optical pyrometers are often used where it is impracticable to use the thermo-couple, either because the temperature is so high that it would destroy the couple, or the heat to be measured is inaccessible to the couple of ordinary length. The temperatures of slag or metal in furnaces or running through tap-holes or troughs are often measured with optical pyrometers. In one type of optical pyrometer, the observer focuses it on the metal or slag and moves an adjustable dial or gage so as to get an exact comparison between the color of the heat measured with the color of a lamp or screen in the pyrometer itself. This, of course, requires practice, and judgment, and brings in the per- sonal equation. With care, however, very reliable temperature measurements may be made. The temperatures of rails, as they leave the finishing pass of a rolling mill, are measured in this way. Another type of optical pyrometer is focused on the body, the temperature of which is to be measured. The rays converge in the telescope on metal cells, heating them, and thereby generating a small electric current, the voltage of which is read on a cali- brated voltmeter similar to that used with the thermo-couple. The best precision is obtained when an optical pyrometer is used each time under similar conditions of light and the same observer. PYROMETRY AND PYROMETERS 207 Where it is impracticable to use either thermo-couples or optical pyrometers. " sentinels" may be used. There are small cones or cylinders made of salts or other substances of known melting points and covering a wide range of temperatures. If six of these "sentinels," melting respectively at 1,300°, 1,350°, 1,400°, 1,450°, 1,500°, and 1,550°F., were placed in a row in a furnace, together with a piece of steel to be treated, and the whole heated up uniformly, the sentinels would melt one by one and the observer, by watching them through an opening in the furnace, could tell when his furnace is at say 1,500° or between 1,500° and 1,550°, and regulate the heat accordingly. A very accurate type of pyrometer, but one not so commonly used as those previously described, is the resistance pyrometer. In this type, the temperature is determined by measuring the resistance to an electric current of a wire which is at the heat to be measured. This wire is usually of platinum, wound around a quartz tube, the whole being placed in the furnace. When the wire is at the temperature of the furnace, it is connected by wires with a Wheatstone Bridge, a delicate device for measuring electrical resistance, and an electric current is passed through the wire. This current is balanced by switching in resistances in the Wheatstone Bridge, until a delicate electrical device shows that no current is flowing. The resistance of the platinum wire at the heat to be measured is thus determined on the '' Bridge," and the temperature read off on a calibration chart, which shows the resistance at various temperatures. These are the common methods used to-day for measuring tem- peratures, but whatever method is used, the observer should bear in mind that the greatest precision is obtained, and hence the highest efficiency, by keeping the apparatus in good working order, making sure that conditions are the same each time, and calibrating or checking against a standard at regular intervals. THE PYROMETER AND ITS USE In the heat treatment of steel, it has become absolutely neces- sary that a measuring instrument be used which will give the operator an exact reading of heat in furnace. There are a number of instruments and devices manufactured for this purpose but any instrument that will not give a direct reading without any guess work should have no place in the heat-treating department. A pyrometer installation is very simple and any of the leading 208 THE WORKING OF STEEL makers will furnish diagrams for the correct wiring and give detailed information as to the proper care of, and how best to use their particular instrument. There are certain general principles, however, that must be observed by the operator and it cannot be too strongly impressed upon them that the human factor involved is always the deciding factor in the heat treatment of steel. A pyrometer is merely an aid in the performance of doing good work, and when carefully observed will help in giving a uniformity of product and act as a check on careless operators. The oper- ator must bear in mind that although the reading on the pyro- meter scale gives the direct heat of furnace where pyrometer-rod or "py-rod" is inserted, it will not give the temperature of the work in furnace, unless by predetermined tests, the heat for penetrating a certain bulk of material has been decided on, and the time necessary for such penetration is known. Each quality of steel, made up of separate analyses, needs a certain heat to determine its critical point, and the elements of which the steel is composed carries a certain time limit which is necessary for the thorough solution of such elements in and above the critical point of temperature. When all these factors are known, and standards set, a pyrometer and clock, with an oper- ator willing to work to orders given, no trouble will arise in the proper heat treatment of steel. Experience has taught us that the time factor is of greater importance than the exact reading of temperature, as fortunately the limits between the critical range, i.e., the decalescent vs. recalescent point has a wide variation, but the time limit for the soaking or solution point of the elements is practically a constant factor, therefore, a clock is as necessary to the proper pyrometer equipment as the pyrometer itself. For the purpose of general work where a wide range of steels or a variable treatment is called for, it becomes necessary to have the pyrometer calibrated constantly, and when no master instrument is kept for this purpose the following method can be used to give the desired results : CALIBRATION OF PYROMETER WITH COMMON SALT An easy and convenient method for standardization and one which does not necessitate the use of an expensive laboratory equipment is that based upon determining the melting point of common table salt (sodium chloride). While theoretically salt PYROMETRY AND PYROMETERS 209 that is chemically pure should be used (and this is neither expen- sive nor difficult to procure), commerical accuracy may be ob- tained by using common table salt such as is sold by every grocer. The salt is melted in a clean crucible of fireclay, iron or nickel, either in a furnace or over a forge-fire, and then further heated until a temperature of about 1,600 to 1,650°F. is attained. It is essential that this crucible be clean because a slight admixture of a foreign substance might noticeably change the melting point. The thermo-couple to be calibrated is then removed from its protecting tube and its hot end is immersed in the salt bath. When this end has reached the temperature of the bath, the crucible is removed from the source of heat and allowed to cool, and cooling readings are then taken every 10 sec. on the milli- voltmeter or pyrometer. A curve is then plotted by using time and temperature as coordinates, and the temperature of the freezing point of salt, as indicated by this particular thermo- couple, is noted, i.e., at the point where the temperature of the bath remains temporarily constant while the salt is freezing. The length of time during which the temperature is stationary depends on the size of the bath and the rate of cooling, and is not a factor in the calibration. The melting point of salt is 1,472°F., and the needed correction for the instrument under observation can be readily applied. It should not be understood from the above, however, that the salt-bath calibration cannot be made without plotting a curve; in actual practice at least a hundred tests are made without plotting any curve to one in which it is done. The observer, if awake, may reasonably be expected to have sufficient appreciation of the lapse of time definitely to observe the temperature at which the falling pointer of the instrument halts. The gradual dropping of the pointer before freezing, unless there is a large mass of salt, takes place rapidly enough for one to be sure that the temperature is constantly falling, and the long period of rest during freezing is quite definite. The procedure of detecting the solidification point of the salt by the hesitation of the pointer without plotting any curve is suggested because of its simplicity. Complete Calibration of Pyrometers. — For the complete cali- bration of a thermo-couple of unknown electromotive force, the new couple may be checked against a standard instrument, placing the two bare couples side by side in a suitable tube and taking frequent readings over the range of temperatures desired. 14 210 THE WORKING OF STEEL If only one instrument, such as a millivoltmeter, is available, and there is no standard couple at hand, the new couple may be calibrated over a wide range of temperatures by the use of the following standards : Water, boiling point 212°F. Tin, under charcoal, freezing point 450°F. Lead, under charcoal, freezing point 621°F. Zinc, under charcoal, freezing point 786°F. Sulphur, boiling point 832°F. Aluminum, under charcoal, freezing point. . . . 1,216°F. Sodium chloride (salt), freezing point. 1,474°F. Potassium sulphate, freezing point 1,958°F. A good practice is to make one pyrometer a standard; calibrate it frequently by the melting-point-of-salt method, and each morn- ing check up every pyrometer in the works with the standard, making the necessary corrections to be used for the day's work. By pursuing this course systematically, the improved quality of the product will much more than compensate for the extra work. The purity of the salt affects its freezing or melting point. Different authorities give temperatures varying by 50°. It is suggested that a sufficient quantity for an extended period of salt be secured. Test the melting point with a pyrometer of known accuracy. Knowing this temperature it will be easy to calibrate other pyrometers. The salt should be kept free from dirt and other additional impurities. Placing of Pyrometers. — When installing pyrometer, care should be taken that it is not placed within direct heat of furnace or furnaces, as this would have the effect of not giving a true reading. When calibrating such an instrument, the potential drop in voltage must be figured, and such drop must be added to heat wanted. When having multiple connections, in other words, when a number of furnaces are connected up in series, and multiple switch is used for control, it becomes apparent that, for uni- formity of product from each furnace, the furnaces furthest away from the reading instrument must have potential drop figured out correctly. This calibration can be done by connecting the master instru- ment with each furnace separately, and watch reading given on pyrometer connected with multiple switch. In this connection, PYROMETRY AND PYROMETERS 211 be sure that cold junction point has been tested, and is in perfect working condition. Py-rods should be tested very often, and it is important that no foreign substance is allowed to freeze in the tube, so that enclosed point becomes a part of a solid mass with outside pro- tecting tube. Wires over the furnaces must be carefully in- spected from time to time, as no true reading can be had on instrument, if insulation is burned off. Where standard calibrating instrument is used, the dry battery in connection with them should be tested before using, so as to be sure that both amperes and voltage is correct. THE LEEDS AND NORTHRUP POTENTIOMETER SYSTEM The potentiometer pyrometer system is both flexible and sub- stantial in that it is not affected by the jar and vibration of the fac- tory or the forge shop. Large or small couples, long or short leads can be used without adjustment. The recording instru- ment may be placed where it is most convenient, without regard to the distance from the furnace. Its Fundamental Principle. — The potentiometer is the elec- trical equivalent of the chemical balance, or balance arm scales. Measurements are made with balance scales by varying known weights until they equal the unknown weight. When the two are equal the scales stand at zero that, is, in the position which they occupy when there is no weight on either pan; the scales are then said to be balanced. Measurements are made with the potentiometer by varying a known electromotive force until it equals the unknown; when the two are equal the index of the potentiometer, the galvanometer needle, stands motionless as it is alternately connected and disconnected. The variable known weights are units separate from the scales, but the potentiometer provides its own variable known electromotive force. The potentiometer provides, first, a means of securing a known variable electromotive force and, second, suitable electrical con- nections for bringing that electromotive force to a point where it may be balanced against the unknown electromotive force of the couple. The two are connected with opposite polarity, or so that the two e.m.f.s oppose one another. So long as one is stronger than the other a current will flow through the couple; when the two are equal no current will flow. Figure 100 shows the wiring of the potentiometer in its simplest 212 THE WORKING OF STEEL form. The thermo-couple is at H, with its polarity as shown by the symbols + and — . It is connected with the main circuit of the potentiometer at the fixed point D and the point G. A current from the dry cell Ba is constantly flowing through the main, or so-called potentiometer circuit, ABCDGEF. The section DGE of this circuit is a slide wire, uniform in resistance Fig. 100. — Simple potentiometer. throughout its length. The scale is fixed on this slide wire. The current from the cell Ba as it flows through DGE, undergoes a fall in potential, setting up a difference in voltage, that is, an elec- tromotive force, between D and E. There will also be electro- motive force between D and all other points on the slide wire. Fig. 101. — Standard cell potentiometer. The polarity of this is in opposition to the polarity of the thermo- couple which connects into the potentiometer at D and at G. By moving G along the slide wire a point is found where the voltage between D and G in the slide wire is just equal to the voltage between D and G generated by the thermo-couple. A gal- vanometer in the thermo-couple circuit indicates when the PYROMETRY AND PYROMETERS 213 balance point is reached, since at this point the galvanometer needle will stand motionless when its circuit is opened and closed. The voltage in the slide wire will vary with the current flowing through it from the cell Ba and a means of standardizing this is provided. SC, Fig. 101, is a cadmium cell whose voltage is con- stant. It is connected at two points C and D to the potentiometer circuit whenever the potentiometer current is to be standardized. At this time the galvanometer is thrown in series with SC. The variable rheostat R is then adjusted until the current flowing is such that as it flows through the standard resistance CD, the fall in potential between C and D is just equal to the voltage of the standard cell SC. At this time the galvanometer will indicate a balance in the same way as when it was used with a thermo- couple. By this operation the current in the slide wire DGE has been standardized. Development of the Wiring Scheme of the Cold-end Compen- sator. — The net voltage generated by a thermo-couple depends Fig. 102. — Hand adjusted cold-end compensator. upon the temperature of the hot end and the temperature of the cold end. Therefore, any method adopted for reading tempera- ture by means of thermo-couples must in some way provide a means of correcting for the temperature of the cold end. The potentiometer may have either of two very simple devices for this purpose. In one form the operator is required to set a small index to a point on a scale corresponding to the known cold junction temperature. In the other form an even more simple automatic compensator is employed. The principle of each is described in the succeeding paragraphs, in which the assumption is made that the reader already understands the potentiometer principle as described above. 214 THE WORKING OF STEEL As previously explained the voltage of the thermo-couple is measured by balancing it against the voltage drop DG in the potentiometer. As shown in Fig. 101, the magnitude of the balancing voltage is controlled by the position of G. Make D movable as shown in Fig. 102 and the magnitude of the voltage DG may be varied either from the point D or the point G. This gives a means of compensating for cold end changes by setting the slider D. As the cold end temperature rises the net voltage generated by the couple decreases, assuming the hot end temperature to be con- stant. To balance this decreased voltage the slider D is moved along its scale to a new point nearer G. In other words, the slider D is moved along its scale until it corresponds to the known temperature of the cold end and then the potentiometer is bal- Fig. 103.— Another type of compensator. anced by moving the slider G. The readings of G will then be direct The same results will be obtained if a slide wire upon which D bears is in parallel with the slide wire of G, as shown in Fig. 103. Automatic Compensator. — It should be noted that the effect of moving the contact D, Fig. 103, is to vary the ratio of the resistances on the two sides of the point D in the secondary slide wire. In the recording pyrometers, an automatic compensator is employed. This automatic compensator varies the ratio on the two sides of the point D in the following manner : The point D, Fig. 104, is mechanically fixed; on one side of D is the constant resistance coil M, on the other the nickel coil N. N is placed at or near the cold end of the thermo-couple (or couples). Nickel has a high temperature coefficient and the electrical proportions of M and N are such that the resistance PYROMETRY AND PYROMETERS 215 change of N, as it varies with the temperature of the cold end, has the same effect upon the balancing voltage between D and G that the movement of the point D, Fig. 104, has in the hand- operated compensator. Instruments embodying these principles are shown in Figs. 105 to 107. The captions making their uses clear. Fig. 104. — Automatic cold-end compensator. PLACING THE THERMO-COUPLES The following illustrations from the Taylor Instrument Company show different applications of the thermo-couples to Fig. 105. — Potentiometer ready for use. furnaces of various kinds. Figure 108 shows an oil-fired furnace with a simple vertical installation. Figure 109 shows a method 216 THE WORKING OF STEEL of imbedding the thermo-couple in the floor of a furnace so as to require no space in the heating chamber. Two methods of applying a pyrometer to a gas furnace are shown in Fig. 110. The vertical method is to be preferred in Fig. 106. — Eight-point recording pyrometer — Carpenter Steel Co. most cases. Figure 111 shows how to connect four furnaces to one pyrometer and recording equipment. Figure 112 is a simple application to a lead or babbit tank. The instrument is light and portable, and can be sighted as PYROMETRY AND PYROMETERS 217 Fig. 107. — Multiple-point thermocouple recorder — Bethlehem Steel Co. SIDE ELEVATION-(SECTIONAL) FRONT ELEVATION Fig. 108. — Tycos pyrometer in oil-fired furnace. 218 THE WORKING OF STEEL easily as an opera glass. The telescope, which is held in the hand, weighs on 25 oz.; and the case containing the battery, **PROVEP_ BY- Fig. 109. — Thermocouple in floor of furnace. Fig. 110. — Pyrometer in gas furnace. rheostat and milliammeter, which is slung from the shoulder, only 10 lb. A large surface to sight at is not required. So long as the image formed by the objective is broader than the lamp fila- ment, the temperature can be measured accurately. PYROMETRY AND PYROMETERS 219 Fig. 111. — Tycos multiple indicating pyrometer and recorder. INDICATOR METAL BATH- TO INDICATOR' Fig. 112. — Pyrometer in galvanizing tank. 220 THE WORKING OF STEEL Distance does not matter, as the brightness of the image formed by the lens is practically constant, regardless of the distance of the instrument from the hot object. The manipulation is simple and rapid, consisting merely in the turning of a knurled knob. The setting is made with great precision, due to the rapid change in light intensity with change LAMP oajecrwa w\Aaaa Fig. 113. — Leeds & Northrup optical pyrometer. in temperature and to the sensitiveness of the eye to differ- ences of light intensity. In the region of temperatures used for hardening steel, for example, different observers using the instrument will agree within 3°C. Only brightness, not color, of light is matched, as light of only one color reaches the eye. Color blindness, therefore, is Fig. 114.— Too low. Fig. 115. — Too high. Fig. 116.— Correct. no hindrance to the use of this method. The use of the instru- ment is shown in Fig. 117. Optical System and Electrical Circuit of the Leeds & Northrup Optical Pyrometer. — For extremely high temperature, the optical pyrometer is largely used. This is a comparative method. By means of the rheostat the current through the lamp is adjusted PYROMETRY AXD PYROMETERS 221 until the brightness of the filament is just equal to the brightness of the image produced by the lens L, Fig. 113, whereupon the filament blends with or becomes indistinguishable in the back- ground formed by the image of the hot object. This adjustment can be made with great accuracy and certainty, as the effect of radiation upon the eye varies some twenty times faster than does the temperature at 1,600°F., and some fourteen times faster at 3,400°F. When a balance has been obtained, the observer notes the reading of the milliammeter. The temperature correspond- ing to the current is then read from a calibration curve supplied with the instrument. Fig. 117. — Using the optical pyrometer. As the intensity of the light emitted at the higher temperatures becomes dazzling, it is found desirable to introduce a piece of red glass in the eye piece at R. This also eliminates any question of matching colors, or of the observer's ability to distinguish colors. It is further of value in dealing with bodies which do not radiate light of the same composition as that emitted by a black body, since nevertheless the intensity of radiation of any one color from 222 . THE WORKING OF STEEL such bodies increases progressively in a definite manner as the temperature rises. The intensity of this one color can therefore be used as a measure of temperature for the body in question. Figures 114 to 116 show the way it is read. CORRECTION FOR COLD-JUNCTION ERRORS The voltage generated by a thermo-couple of an electric pyrometer is dependent on the difference in temperature be- tween its hot junction, inside the furnace, and the cold junc- tion, or opposite end of the thermo-couple to which the copper wires are connected. If the temperature of this cold junction rises and falls, the indications of the instrument will vary, although the hot junction in the furnace may be at a constant temperature. A cold-junction temperature of 75°F., or 25°C, is usually adopted in commercial pyrometers, and the pointer on the pyrometer should stand at this point on the scale when the hot junction is not heated. If the cold-junction temperature rises about 75°F., where base metal thermo-couples are used, the pyrometer will read approximately 1° low for every 1° rise in temperature above 75°F. For example, if the instrument is adjusted for a cold-junction temperature of 75°, and the actual cold-junction temperature is 90°F., the pyrometer will read 15° low. If, however, the cold-junction temperature falls below 75°F., the pyrometer will read high instead of low, approximately 1° for every 1° drop in temperature below 75°F. With platinum thermo-couples, the error is approximately ]>4° for 1° change in temperature. Correction by Zero Adjustment. — Many pyrometers are supplied with a zero adjuster, by means of which the pointer can be set to any actual cold-junction temperature. If the cold junction of the thermo-couple is in a temperature of 100°F., the pointer can be set to this point on the scale, and the readings of the instrument will be correct. Compensating Leads. — By the use of compensating leads, formed of the same material as the thermo-couple, the cold junction can be removed from the head of the thermo-couple to a point 10, 20 or 50 ft. distant from the furnace, where the temperature is reasonably constant. Where greater accuracy is desired, a common method is to drive a 2-in. pipe, with a pointed closed end, some 10 to 20 ft. into the ground, as shown PYROMETRY AND PYROMETERS 223 in Fig. 118. The compensating leads are joined to the copper leads, and the junction forced down to the bottom of the pipe. The cold junction is now in the ground, beneath the building, at a depth at which the temperature is very constant, about 70°F., throughout the year. This method will usually control the cold-junction temperature within 5°F. Where the greatest accuracy is desired a compensating box will overcome cold-junction errors entirely. It consists of a case enclosing a lamp and thermostat, which can be adjusted Fig. 118. — Correcting cold-junction error. to maintain any desired temperature, from 50 to 150°F. The compensating leads enter the box and copper leads run from the compensating box to the instrument, so that the cold junction is within the box. Figure 119 shows a Brown compensating box. If it is desired to maintain the cold junction at 100°: the thermostat is set at this point, and the lamp, being wired to the 110- or 220-volt lighting circuit, will light and heat the box until 100° is reached, when the thermostat will open the circuit and 224 THE WORKING OF STEEL the light is extinguished. The box will now cool down to 98°, when the circuit is again closed, the lamp lights, the box heats up, and the operation is repeated. These will compensate for a number of thermo-couples. Fig. 119. — Compensating box. BROWN AUTOMATIC SIGNALING PYROMETER In large heat-treating plants it has been customary to maintain an operator at a central pyrometer, and by colored electric Fig. 120. — Brown automatic signaling pyrometer. lights at the furnaces, signal whether the temperatures are correct or not. It is common practice to locate three lights above each furnace — red, white and green. The red light burns when the temperature is too low, the white light when the temperature is within certain limits — for example, 20°F. of the correct temperature — and the green light when the temperature is too high. Instruments to operate the lights automatically have been PYROMETRY AND PYROMETERS 225 devised and one made by Brown is shown in Fig. 120. The same form of instrument is used for this purpose to auto- matically control furnace temperatures, and the pointer is depressed at intervals of every 10 sec. on contacts corresponding to the red, white and green lights. Fig. 121.— Automatic temperature control. AN AUTOMATIC TEMPERATURE CONTROL PYROMETER Automatic temperature control instruments are similar to the Brown indicating high resistance pyrometer with the excep- tion that the pointer is depressed at intervals of every 10 sec. upon contact-making devices. No current passes through the pointer which simply depresses the upper contact device tipped with platinum, which in turn comes in contact with the lower contact device, platinum-tipped, and the circuit is completed through these two contacts. The current is very small, about 15 226 THE WORKING OF STEEL }?{o amp., as it is only necessary to operate the relay which in turn operates the switch or valve. A small motor is used to depress the pointer at regular intervals. The contact-making device is adjustable throughout the scale range of the instru- ment, and an index pointer indicates the point on the in- strument at which the temperature is being controlled. The space between the two contacts on the high and low side, Fig. 122. — Portable thermocouple testing molten brass. separated by insulating material, is equivalent to 1 per cent of the scale range. A control of temperature is therefore pos- sible within 1 per cent of the total scale range. Figure 121 shows this attached to a small furnace. PYROMETERS FOR MOLTEN METAL Pyrometers for molten metal are connected to portable thermo-couples as in Fig. 122. Usually the pyrometer is port- able, as shown in this case which is a Brown. Other methods of mounting for this kind of work are shown in Figs. 123 to 124. The bent mountings designed for molten metal, such as brass or copper and is supplied with either clay, graphite or carborun- dum tubes. Fifteen feet of connecting wire is usually supplied. The angle mountings, Fig. 124, are recommended for baths such as lead or cyanide. The horizontal arm is usually about 14 in. long, and the whole mounting is easily taken apart making PYROMETRY AND PYROMETERS 227 replacements very easy. Details of the thermo-couple shown in Fig. 122 are given in Fig. 125. This is a straight rod with a protector for the hand of the operator. The lag in such couples is less than one minute. These are Englehard mountings. PROTECTORS FOR THERMO-COUPLES Thermo-couples must be protected from the danger of mechan- ical injury. For this purpose tubes of various refractory materials are made to act as protectors. These in turn are usually protected by outside metal tubes. Pure wrought iron is largely used for this purpose as it scales and oxidizes very Fig. 123. — Bent handle thermocouple with protector. slowly. These tubes are usually made from 2 to 4 in. shorter than the inner tubes. In lead baths the iron tubes often have one end welded closed and are used in connection with an angle form of mounting. Where it is necessary for protecting tubes to project a con- siderable distance into the furnace or tube made of nichrome is frequently used. This is a comparatively new alloy which stands high temperatures without bending. It is more costly than iron but also much more durable. When used in portable work and for high temperatures, pure nickel tubes are sometimes used. There is also a special metal tube made for use in cyanide. This metal withstands the intense penetrating characteristics of cyanide. It lasts from six to ten months as against a few days for the iron tube. 228 THE WORKING OF STEEL The inner tubes of refractory materials, also vary according to the purposes for which they are to be used. They are as follows : Marquardt mass tubes for temperatures up to 3,000°F., but they will not stand sudden changes in temperature, such as in contact with intermittent flames, without an extra outer covering of chamotte, fireclay or carborundum. Fig. 124. — Other styles of bent mounting. Fused silica tubes for continuous temperatures up to 1,800°F. and intermittently up to 2,400°F. The expansion at various temperatures is very small, which makes them of value for portable work. They also resist most acids. Chamotte tubes are useful up to 2,800°F. and are mechanically strong. They have a small expansion and resist temperature PYROMETRY AND PYROMETERS 229 changes well, which makes them good as outside protectors for more fragile tubes. They cannot be used in molten metals, or baths of any kind nor in gases of an alkaline nature. They are used mainly to protect a Marquardt mass or silica tube. Carborundum tubes are also used as outside protection to other tubes. They stand sudden changes of temperature well and resist all gases except chlorine, above 1,750°F. Especially useful in protecting other tubes against molten aluminum, brass, copper and similar metals. Clay tubes are sometimes used in large annealing furnaces where they are cemented into place, forming a sort of well for the insertion of the thermo-couple. They are also used with portable thermo-couples for obtaining the temperatures of molten iron and steel in ladles. Used in this way they are naturally short-lived, but seem the best for this purpose. Fig. 125. — Straight thermocouple and guard. Corundite tubes are used as an outer protection for both the Marquardt mass and the silica tubes for kilns and for glass fur- naces. Graphite tubes are also used in some cases for outer protections. Calorized tubes are wrought iron pipe treated with no alumi- num oxide which often doubles or even triples the life of the tube at high temperature. These tubes come in different sizes and lengths depending on the uses for which they are intended. Heavy protecting outer tubes may be only 1 in. in inside diameter and as much as 3 in. outside diameter, while the inner tubes, such as the Marquardt mass and silica tubes are usually about % in. outside and % in. inside diameter. The length varies from 12 to 48 in. in most cases. Special terminal heads are provided, with brass binding posts for electrical connections, and with provisions for water cooling when necessary. APPENDIX Table 32. —Temperature Conversion Tables. Table 33.— Comparison Between Degrees Centigrade and Degrees Fahrenheit. Table 34. — Weight of Round, Octagon and Square Carbon Tool Steel per Foot. Table 35. — Weight of Round Carbon Tool Steel 12 In. in Diameter and Larger, per Foot. Table 36. — Decimal Equivalents of a foot. 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CC -f CM o CO CO ■* CM o CO CO ■* CI o O CM 1- co t> OS i- 00 co >o CO A co a - - CM 33 •cB 03 33 1- 03 - ■ r. co ~ CM o CM 5 CI CO CI o CI CM t- 00 t- e- o co co CM 00 eo 00 00 10 oo CO co eo CO co en co o 0) a> CM o> eo 0) >* O) IO 0) CO o> t- O) co 0) O) O) O o O CO rH i> CM CO co o> •* o CO rH l> CM CO CO 03 ■* o CO rt i> CM co 10 io CM CM co CM CO CI CM CM 00 CM co CM 03 CM o co o CO CO CI co CM co co co CO co -r CO IO co >o co CO CC CO CO CC co CO ■* CM O co CO -# CM O CO CD ■* CM o oo CO ■* CM O X CO ■* CM O CM CO CO 00 CC X CO OS 33 CO 03 CO 03 CO OS o CM IO c l> 33 O 2 CO ■* co X O CI t- oo CM CM O) CM o eo eo CM eo eo eo eo 10 eo CC eo eo CO eo o> eo o 1-1 CM eo * ■* IO CO co en CO CM t- CM CO M co CO £ CO CM CM CO l> co CO 03 00 ■CH c s co IO rt CO CM CI oo eo CO 03 00 ■* •* CM CM 1 1 1 1 o 1 O o 1-1 r-i CM CM CO co ■* IO IO CO o t> l> co 00 OS CO o CM .-h CO CO 1 1 CM - CI 1 CM 1 co IO 01 1 CO CO CM 1 o CI CM 1 CM ~ CM 1 1 CO 'O 1 CO -t 1 o CC 1 CM 1 03 1 CO 1 co 1 1 CI CM 1 1 •* CM CO o o O 0) o 00 O O CO o o O eo © CM o o o o 0) O CO o o CO o IO o o eo o CM o o CO o ■* 33 1 co 1 CO 1 CM 1 l> 1 1 CO o ■* 03 1 co co C3 CO CM CM 1 1 X -J CM 1 1 o 1 «o 03 1 o - 1 CO 1 co 1 co i- 1 1> CO 1 CM CO 1 CO 1 IO 1 IO 1 O -r 1 co 1 CO CM 1 eo CI 1 j 00 xc r(i CM O C/J PT| - CM rH CO oo O H ( ) CO c- CO en o < w W, eo 03 rH ra CO co ori •* - to O u CO CO ■* IO IO H on CO ■* CM o ■* h, H T •-i OS o P-, H CM eo ^H m CO ,-j K CM on IO CO r^ K U - • L4 v O h h m M i. _SJ co co fi co CO 01 r- t; C m cs e ^| , CO CO r^S 'n « >i ts g, o ■■5 ^ ^ M R =3 5 O J33 ^ a a 2q c H ^2 j=i ■S O ° to fe "" ° « > co co c3 O — i +> ^ \5.S I- 2 T3 a jd 234 THE WORKING OF STEEL Those using pyrometers will find this and the preceding conversion table of great convenience: Table 33. — Comparison Between Degrees Centigrade and Degrees Fahrenheit Degrees Degrees Degrees Degrees Degrees Degrees Degrees F. C. F. C. F. C. F. C. F. C. F. C. F. C. -40 -40.0 3 -16.1 40 7.7 89 31.6 132 55.5 175 79.4 275 135.0 -39 -39.4 4 -15.5 47 8.3 90 32.2 133 56.1 176 80.0 300 148.8 -38 -38.8 5 -15.0 48 8.8 91 32.7 134 56.6 177 80.5 325 162.7 -37 -38.3 6 -14.4 4!) 9.3 92 33.3 135 57.2 178 81.1 350 176.6 -36 -37.7 7 -13.8 50 10.0 93 33.9 136 57.7 179 81.6 375 190.5 -35 -37.2 8 -13.3 51 10.5 94 34.4 137 58.3 180 82.2 400 204.4 -34 -36.6 9 -12.7 52 11.1 95 35.0 138 58.8 181 82.7 425 218.3 -33 -36.1 10 -12.2 53 11.6 96 35.5 139 59.4 182 83.3 450 232.2 -32 -35.5 1J -11.6 54 12.2 97 36.1 140 60.0 183 83.8 475 246.1 -31 -35.0 12 -11.1 55 12.7 98 36.6 141 60.5 184 84.4 500 260.0 -30 -34.4 18 -10.5 56 13.3 99 37.2 142 61.1 185* 85.0 525 273.8 -29 -33.9 14 -10,0 57 13.8 100 37.7 143 61.6 186 85.5 550 287.7 -28 -33.3 15 - 9.3 58 14.4 101 38.3 144 62.2 187 86.1 575 301.6 -27 -32.7 10 - 8.8 59 15.0 102 38.8 145 62.7 188 86.6 600 315.5 -26 -32.2 17 - 8.3 GO 15.5 103 39.4 146 63.3 189 87.2 625 329.4 -25 -31.6 IS - 7.7 01 16.1 104 40.0 147 63.8 190 87.7 650 343.3 -24 -31.1 19 - 7.2 02 16.6 105 40.5 148 64.4 191 88.3 675 357.2 -23 -30.5 20 - 6.6 63 17.2 106 41.1 149 65.0 192 88.8 700 371.1 -22 -30.0 21 - 6.1 64 17.7 107 41.6 150 65.5 193 89.4 725 385.0 -21 -29.4 22 - 5.5 65 18.3 108 42.2 151 66.1 194 90.0 750 398.8 -20 -28.8 23 - 5.0 66 18.8 109 42.7 152 66.6 195 90.5 775 412.7 -19 -28.3 24 - 4.4 67 19.4 110 43.3 153 67.2 196 91.1 800 426.6 -18 -27.7 25 - 3.8 68 20.0 111 43.8 154 67.7 197 91.6 825 440.5 -17 -27.2 20 - 3.3 69 20.5 112 44.4 155 68.3 198 92.2 850 454.4 -16 -26.6 27 - 2.7 70 21.1 113 45.0 156 68.8 199 92.7 875 468.3 -15 -26.1 28 - 2.2 71 21.6 114 45.5 157 69.4 200 93.3 900 482.2 -14 -25.5 29 - 1.6 72 22.2 115 46.1 158 70.0 201 93.8 925 496.1 -13 -25.0 30 - 1.1 73 22.7 116 46.6 159 70". 5 202 94.4 950 510.0 -12 -24.4 31 - 0.5 74 23.3 117 47.2 160 71.1 203 95.0 975 523.8 -11 -23.8 32 - 0.0 75 23.8 118 47.7 161 71.6 204 95.5 1,000 537.7 -10 -23.3 33 + 0.5 70 24.4 119 48.3 162 72.2 205 96.1 1,100 593.3 - 9 -22.7 34 1.1 77 25.0 120 48.8 163 72.7 206 96.6 1,200 648.8 - 8 -22.2 35 1.6 78 25.5 121 49.4 164 73.3 207 97.2 1,300 704.4 - 7 -21.6 36 2.2 79 26.1 122 50.0 165 73.8 208 97.7 1,400 760.0 - 6 -21.1 37 2.7 80 26.6 123 50.5 166 74.4 209 98.3 1,500 815.5 - 5 -20.5 38 3.3 81 27.2 124 51.1 167 75.0 210 98.8 1,600 871.1 - 4 -20.0 39 3.8 82 27.7 125 51.6 168 75.5 211 99.4 1,700 926.6 - 3 -19.4 40 4.4 83 28.3 126 52.2 169 76.1 212 100.0 1,800 982.2 - 2 -18.8 41 5.0 84 28.8 127 52.7 170 76.6 213 100.5 1,900 1,037.7 - 1 -18.3 42 5.5 85 29.4 128 53.3 171 77.2 214 101.1 2,000 1,093.3 -17.7 43 6.1 80 30.0 129 53.8 172 77.7 215 101.6 2,100 1,148.8 + 1 -17.2 44 6.6 87 30.5 130 54.4 173 78.3 225 107.2 2,200 1,204.4 2 -16.6 45 7.2 88 31.1 131 55.0 174 78.8 250 121.1 2,300 1,260.0 9 x degrees C. Degrees Fahrenheit = h 32 Degrees Centigrade 5 x (degrees F. - 32) PYROMETRY AND PYROMETERS 235 Three other useful tables are also given on the following pages. Table 34. — Weight of Round, Octagon and Squake Carbon Tool Steel per Foot Size Size in Round Octagon Square in Round Octagon Square inches inches He 0.010 0.011 0.013 2M 16.79 17.71 21.37 X 0.042 0.044 0.053 2% 18.51 19.52 23.56 Ms 0.094 0.099 0.120 2H 20.31 21.42 25.86 X 0.168 0.177 0.214 2% 22.20 23.41 28.27 5 /U 0.262 0.277 0.334 3 24.17 25.50 30.78 X 0.378 0.398 0.481 ZX 26.23 27.66 33.40 Ke 0.514 0.542 0.655 ZX 28.37 29.92 36.12 X 0.671 0.708 0.855 3% 30.59 32.27 38.95 Kg 0.850 0.896 1.082 ZX 32.90 34.70 41.89 Vs 1.049 1.107 1.336 z% 35.29 37.23 44.94 %. 1.270 1.339 1.616 m 37.77 39.84 48.09 % 1.511 1.594 1.924 ZX 40.33 42.54 51.35 13 /l6 1.773 1.870 2.258 4 42.97 45.34 54.72 X 2.056 2.169 2.618 4M 48.51 51.17 61.77 15 /lG 2.361 2.490 3.006 ±X 54.39 57.37 69.25 1 2.686 2.833 3.420 4% 60.60 63.92 77.16 M 3.399 3.585 4.328 5 67.15 70.83 85.50 IK 4.197 4.427 5.344 5X 74.03 78.08 94.26 i% 5.078 5.356 6.646 5X 81.25 85.70 103.45 IX 6.044 6.374 7.695 5% 88.80 93.67 113.07 l« 7.093 7.481 9.031 6 96.69 101.99 123.12 1M 8.226 8.674 10.474 7 131.61 138.82 167.58 i% 9.443 9.960 12.023 8 171.90 181.32 218.88 2 10.744 11.332 13.680 9 217.57 229.48 277.02 2M 12.129 12.793 15.443 10 268.60 283.31 342.00 2K 13.598 14.343 17.314 11 325.01 342.80 413.82 2% 15.151 15.981 19.291 12 386.79 407.97 492.48 High-speed steel, being more dense than carbon steel, weighs from 10 to 11 per cent more than carbon steel. This should be added to figures given in the table. 236 THE WORKING OF STEEL Table 35. — Weight of Round, Carbon Tool Steel 12 In. in Diameter and Larger, per Foot Diameter, Weight Diameter, Weight Diameter, Weight inches per foot inches per foot inches per foot 12 386.790 15% 677.527 19% .1,049.010 12% 395.518 16 687.600 19% 1,061.705 12% 404.246 16% 699.017 20 1,074.400 12% 412.974 16% 710.435 20% 1,088.502 12% 421 . 702 16% 721.852 20% 1,102.605 12% 430.430 16% 733.270 20% 1,116.707 12% 439.158 16% 744.687 20% 1,130.810 12% 447.886 16% 756.105 20% 1,144.912 13 456.615 16% 767.522 20% 1,159.015 13% 465.343 17 778.940 20*% 1,173.118 13% 474.071 17% 790.358 21 1,187.220 13% 482.799 17% 801 . 777 21% 1,201.322 13% 491.527 17% 813.195 21% 1,215.425 13% 500.255 17% 824.614 21% 1,229.527 13% 508 . 983 17% 836.030 21% 1,243.630 13% 517.711 . 17% 847.447 21% 1,257.732 14 526.440 17% 858.863 21% 1,271.835 14% 536.512 18 870.280 21% 1,285.937 14% 546.585 18% 883.105 22 1,300.040 14% 556.657 18% 895.920 22% 1,315.485 14% 566.730 18% 908.740 22% 1,330. 930 14% 576.802 18% 921.560 22% 1,346.375 14% 586.875 18% 934.380 22% 1,361.820 14% 596 . 947 18% 947.200 22% 1,377.265 15 607.020 18% 960.020 22% 1,392.710 15% 617.092 19 972.840 22% 1,408.155 15% 627.165 19% 985.035 23 1,423.600 15% 637.237 19% 998.230 23% 1,454.490 15% 647.310 19% 1010.925 23% 1,485.380 15% 657.382 19% 1,023.620 23% 1,516.270 15% 667.455 19% 1,036.315 24 1,547.160 To find the weight of discs made of carbon steel, in diameters up to and including 12 in., without any allowance for finishing multiply the per foot weight of round bar steel, shown herewith by the decimal equivalent of a foot given in the following table : PYROMETRY AND PYROMETERS 237 Table 36. — Decimal Equivalents of a Foot In. H H % V2 Vs H Vs 0.000 0.010 0.021 0.031 0.042 0.052 0.063 0.073 1 0.083 0.094 0.104 0.115 0.125 0.135 0.146 0.156 2 0.167 0.177 0.188 0.198 0.208 0.219 0.229 0.240 3 0.250 0.260 0.270 0.281 0.292 0.302 0.313 0.323 4 0.333 0.344 0.354 0.364 0.375 0.385 0.396 0.406 5 0.416 0.427 0.437 0.448 0.458 0.469 0.479 0.480 6 0.500 0.510 0.520 0.531 0.542 0.552 0.563 0.573 7 0.583 0.594 0.604 0.615 0.625 0.635 0.646 0.656 8 0.666 0.677 0.687 0.698 0.708 0.719 0.729 0.740 9 0.750 0.760 0.770 0.781 0.792 0.802 0.813 0.823 10 J3.833 0.844 0.854 0.865 0.875 0.885 0.896 0.906 11 0.916 0.927 0.937 0.948 0.953 0.969 0.979 0.990 Example. — If the weight of a carbon steel disc 7 in. diameter, \% in. thick is desired, turn to page 233, where the per foot weight of 7 in. round is given as 131.6 lb. Multiply this by the decimal equivalent of 1% in., or 0.135, as shown in the above table, and the product will be the net weight of the disc. 131.61 lb. = the weight of 1 ft. of 7 in. round. 0. 135 = the per foot decimal equivalent of 1% in. 65805 39483 13161 17.76735 lb. = weight of disc 7 in. diam. 1% in. thick without any allowance for finishing. 238 THE WORKING OF STEEL AUTHORITIES QUOTED Addis, W. H., 102 American Machinists' Handbook, 69 American Steel Treaters' Soci- ety, 117 American Gear Mfrs. Asso., Ill Automatic and Electric Fur- naces Ltd., 161 Arnold, Prof. J. O., 167 B Burleigh, R. W. Borden, B. Boker, Herman & Co. Brown Instrument Co., 224 Brown, Lipe Chapin Co., 121 C Campbell Curtis Airplane Co. Carhart, H. A., 42 E Englehard, Charles, 227 Ens aw, Howard, 12, 79, 95 F Firth-Sterling Steel Co., 176 Firth, Thomas & Sons, 137 Fowler, Henry, 151 G Gilbert & Barker, 164, 188 H Hayward, C. R., 35 Howe, Dr. H. M., 8* Hoover Steel Ball Co., 61 Heathcote, H. L., 85 Harris, Matthew, 94 Hunter, J. V., 192 J Janitzky, E. J., 117 Latrobe Steel Co., 150, 178 Ludlum Steel Co., 175 Leeds & Northrup Co., 211 Lyman, W. H., 199 M Mansfield, C. A. Midvale Steel Co. McKenna, Roy C, 164 Moulton, Seth A., 199 N Niles, Bennet, Pond, 67 Parker, S. W. Poole, C. R. S S. A. E. (Society Automatic En- gineers), 39, 46, 49, 134 Sauveur, Albert, 105, 232 Springfield Armory, 78, 120 Sellack, T. G. Smith, A. J., 101 Suverkrop, E. A., 121 Shirley, Alfred J. Taylor Instrument Co., 215 U U. S. Ball Bearing Co. United Steel Co. Underwood, Charles N. V Van Deventer, John H., 86 W Johnston, A. B., 35 Juthe, K. A., 1, 24, 65, 75, 79, 105, Wood, Harold F., 46 145 Wheelock, Lovejoy & Co., 69 INDEX A B C of iron and steel, ix Absorption of carbon, rate of, 83 Air hardening steels, 183 Analysis of high speed steel, 165 Alloy steel, annealing, 76 properties of, 34 Alloys and their effect, 24 in high speed steel, 166 in steel, value of, 14 upon steel, 24 Alpha iron, 22, 105 Annealing, 22 care in, 154, 155 furnace, 190 high-chromium steel, 36 high speed tools, 174 in bone, 77 methods, 122 proper, 114 rifle components, 78 rust-proof steel, 36 steels, 75 temperature, 114 work, 112 Austentite, 22, 106 Automotive industry, application of Liberty engine materials to, 46 temperature control, 225 Axles, heat treatment of, 61 B Balls, making steel, 61 Barium chloride process, 178 Baths for tempering, 157 Bessemer converter, 2 Beta iron, 22, 105 Blending compounds, 103 Blue brittleness, 56 Borax and sand as a flux, x Bone, annealing in, 77 Boxes for case hardening or carburiz- ing, 80 Breaking test gears, 126 Brinell hardness, 13-19 hardness and tensile, 20 test, 116 Broach hardening furnace, 188 Brown automatic pyrometer, 224 Burning, 23 Calescence, 108 Calorized tubes, 229 Carbon, 107 content at various tempera- tures, 84 content of case hardened work, 81 in cast iron, ix in tool steel, 149-150 introduction of, 96 penetration of, 95 steel, 15 steel forgings, Liberty engine, 48 steel tools, 145 steels, S. A. E., 39 steels, temper colors, 163 tool steel, forging, 65 Carbonizing, see Carburizing. Carborundum tubes, 229 Carburization, preventing, 93 Carburizing by gas, 93 boxes, 80 compounds, 102 effect of size, 117 gas consumption by, 101 local, 94 material, 85 nickel steel, 125 or case hardening, 79 239 240 INDEX Carburizing by gas, pots for, 123 process of, 113 short method, 124 sleeves, 132 Car door type of furnace, 190 Case hardening boxes, 80 cast iron, 89 local, 94 or surface carburizing, 79 see Carburizing, Case-hardening steels, 16 treatments for various steels, 92 Cast iron, carbon in, ix case hardening, 89 Case, depth of, 86 "Cementite," 21, 106 Center column furnace, 186 Centigrade table, 232-234 Chamotte tubes, 228 Chart of carbon penetration, 97 and punches, steel for, 151 heat treatment, 151 shape, 151 Chrome steel, 26-27 Chrome-nickel steel, 27-28 steel, forging, 66 Chrome-vanadium steel, 15 Chromium, 26-27, 107 steels, S. A. E., 41 Chromium-cobalt steel, 178 Chromium-vanadium steel, S. A. E., 41 Classification of steel, 11 . Clay tubes, 229 Cold end compensator, 213 junction errors, 222 shortness, 166 worked steel, 65 Color in tempering, 157 Colors on carbon steels, 163 Combination tank, 90 Comparison of fuels, 191 Compensating leads, 222 Compensator for cold ends, 214 automatic, 214 Composition of steel, 12, 105 Compound, blending, 103 separating from work, 102 Compounds for carburizing, 102 Connecting rods, Liberty motor, 42, 52 Continuous heating furnace, 71 Controlling factors, 107 Converter, bessemer, 2 Cooling quenching oil, roof system, 74 rate of for gear-forgings, 51 Copper, effect of in medium carbon steel, 35 Copper-plating to prevent carburiz- ing, 93 Corrosion of high-chromium steel, 38 of rust-proof steel, 38 Corundite tubes, 229 Cost of operating furnaces, 200 Cracks in hardening, preventing, 160 Crankshaft, Liberty motor, 54 Critical point, 112 points, 10, 108 Crucible or tool steel, annealing, 76 Cutting off high speed steel, 172 Cyanide bath for tool steel, 133 D Decalescent point, 11-112 Decarbonizing of outer surface, 153 preventing, 154 Depth of case, 86 Detrimental elements in steel, 166 Dies, drop forging, 133 quenching, 147 soft spots in, 147 tempering round, 161 Drawing, 23 ends of gear teeth, 127 Drop forging dies, 133 E Effect of alloys, 167 of different carburizing ma- terial, 87 of size of piece, 89-117 of copper in medium carbon steel, 35 Electric process of steel making, 4 Elements, different, 107 INDEX 241 Enlarging steel, 161 Equipment for heat treating, 121 "Eutectic," 21 "Eutectoid,"22 Furnaces, tool, 187 water cooled fronts, 197 Fuels, comparison of, 191 for furnaces, 199 F Fahrenheit temperature table, 232- 234 "Ferrite," 21, 106 Fish oil for hardening, 110 Flame shields, 193 Flange shields for furnaces, 197 Flux, borax and sand, x Forging furnace, 189 high speed tools, 174 improper, 66 of steel, 64 practice, heavy, 195 rifle barrels, 69 Forgings, carbon steel Liberty engine, 48 Formed tools, high speed, 174 Fractures, examining by, 159 Furnace, continuous heating, 71 crucible, 4 data, 199 electric, 6 Heroult, 6 open hearth, 3 records, 129 Furnaces, 185 annealing, 190 broach hardening, 188 car door type, 190 center column, 186 cost of operating, 200 data on, 199 forging, heavy, 195 fuels for, 199 gas fired, 190 high speed steel, 187 lead pot, 185 manganese steel, 198 muffle, 189 oil fired, 186 operating costs, 200 screens for, 192 16 G Gages, changes due to quenching, 162 tempering, 161 Gamma iron, 22, 105 Gas, carburizing by, 93 consumption for carburizing, 101 fired furnace, 190 illumination for carburizing, 97 Gear blanks, heat treatment of, 111 forgings, rate of cooling for Liberty engine, 51 hardening machine, 130 steel, transmission, 59 teeth, drawing ends of, 127 Gears, Liberty engine, 50 Gleason tempering machine, 129 Grain, refining, 91 size, 23 Graphitic carbon, ix Grinding high speed steel, 176 II Hair lines in forgings, 56 Hardening carbon steel for tools, 145 cracks, preventing, 160 dies, 146 gears, 130 high speed steel, 171 high speed tools, 177 of high-chromium steel, 37 of rust-proof steel, 37 J room, modern, 146 Heating, effect of size, 117 Heat, judging by color, 110 treating departments, 122 equipment, 121 forgings, 44 inspection of, 125 Liberty motor, 44 nickel chrome steel, 13 242 INDEX Heat, of axles, 61 of chisels, 151 of gears, 131 of high speed steel, 170 of rifle parts, 120 of steel, 105 S. A. E., 134-137 treating, departments, treat- ment, difference in, 14 Heroult furnace, 6 High-chromium steel, 36 annealing of, 36 corrosion of, 38 hardening of, 37 Highly stressed parts of Liberty engine, 49 High speed steel, analysis of, 166 annealing, 75 cutting off, 172 forging, 65 furnace, 187 hardening, 171 heat treatment of, 170 instructions for, 175, 180 manufacture, 166, 169 pack hardening, 172 structure of, 168 Hints for steel users, 159 "Hypo-eutectic,"21 "Hypo-eutectoid,"22 Illuminating gas for carburizing, 97 Improper forging, 66 Influence of size on heating, 117 Inspection of heat treatment, 125 Internal stresses, relieving, 154 Introduction of carbon, 96 Jewelers' tools, 146 Judging heat of steel by color, 110 Lathe and planer tools, 176 tools, high speed, 173 Latrobe temper list, 150 Lead bath, 154 pot furnace, 185 Leeds & Northrup potentiometer, 211 optical pyrometer, 220 Liberty engine, highly stressed parts of, 49 Liberty engine materials, application to automatic industry, 46 motor connecting rods, 42, 52 motor, crankshaft, 54 motor piston pin, 57 Linseed oil for hardening, 110 Local case hardening, 94 Luting mixture, 100 M Machineability of steel, 72 Machinery steel, annealing, 77 Magnet test, 109 Malleable iron, ix Manganese, 29-30, 107 steel, 15, 29-30 furnace, 198 Manufacture of high speed steel, 169 Marquardt mass tubes, 228 Martensite, 22, 106 Medium carbon steel, effect of copper on, 35 Microphotographs, 114 Microscopic examination, 158 Milling cutters, high speed, 174 Mixture for luting, 100 Modern hardening room, 146 Molten metal pyrometers, 226 Molybdenum, 32 Muffle furnace, 189 N Nickel, 107 Nickel-chrome steel, 15-19 Nickel-chromium, 27-28 steels, S. A. E., 40 Nickel, influence of on steel, 25 steel, 24-26 affinity for carbon, 125 steels, 18 S. A. E., 39 INDEX 243 Non-homogeneous melting, 24 Non-shrinking steels, 35 "Normalizing," 22 temperature, 16 O Oil bath for tempering, 157 cooling on roof, 74 fired furnace, .186 for hardening, 110 hardening steel, forging, 66 steels, 35 temperature of quenching, 124 Open hearth furnace, 3 Operating costs of furnaces, 200 Osmondite, 106 Outer surface decarbonizer, 153 Over-heated steel, restoring, 137 Overheating, 23 dies, 148 Pack-hardening, 87 high speed steel, 173 Packing work for carburizing, 123 Paste for hardening dies, 146 "Pearlite,"21, 106 Penetration of carbon, 95 carbon, chart of, 97 in case hardening, 83 Phosphorous, 33 Pickling Liberty motor forgings, 44 Piston pin, Liberty motor, 57 Placing pyrometers, 210 Planer tools, high speed, 173 "Points" of carbon in steel, 9 Potentiometer, Leeds & Northrup, 211 Pots for carburizing, 123 Press for testing gears, 126 Preventing carburization, 93 cracks in hardening, 160 Properties of alloy steels, 34 of alloy steels, table, 34 of steel, 12 Protective screens for furnaces, 192 Puddled iron, ix Punches and chisels, steels for, 151 Py-rod, 208 Pyrometers, 202 calibration, 208 copper ball, 202 indicating, 219 inspection, 208 iron ball, 202 molten metal, 226 optical, 206, 220 placing, 210 recording, 216 Siemens, 202 testing, 209 water, 203 Q Quality and structure of high speed steel, 168 of steel, 149 Quenching, 22 after carburizing, 86-88 dies in tank, 147 obsolete method, 148 oil, temperature of, 124 tank, 89 tool steel, 156 K Rate of absorption of carbon, 83 Recalescence, 109 Recalescent point, 11 Recording temperatures, 127 Red shortness, 166 Refining the grain, 91 Regenerative open hearth furnace, 3 Restoring overheated steel, 137 Rifle barrels, forging, 69 components, annealing, 78 parts, heat treatment of, 120 Roof system of cooling oil, 74 Rust-proof steel, 36 annealing of, 36 corrosion of, 38 hardening of, 37 244 INDEX S S. A. E. carbon steels, 39 chromium steels, 41 chromium-vanadium, 41 heat treatments, 134-137 nickel-chromium steels, 40 nickel steels, 39 screw stock, 39 silico-manganese steel, 41 standard steels, 39 Salt bath for tempering, 157 Sclerescope test, 116 Screens for furnaces, 192 Screw stack, S. A. E., 39 Sentinels, melting of, 207 Separating work from compound, 102 Silversmiths' tools, 146 Size of piece, effect of, 89-117 influence of. 117 Sleeves, carburizing, 132 hardening and shrinking, 132 shrinking, 132 Shields for furnace doors, 193 Short method of carburizing, 124 Shrinking steel, 161 Silica tubes, 228 Silico-manganese steels, S. A. E., 41 Silicon, 33, 107 Sorbite, 22, 106 Specimens, test, 23 Standard S. A. E. steels, 39 Steel balls, stock for, 62 bolts, making, 61 composition of, 105 for chisels and punches, 151 forging of, 64 give it a chance, 148 heat treatment of, 105 high speed, 165 making, 1 bessemer process, 1 crucible process, 4 electric furnace process, 4 open hearth, 1 tools, carbon, in, 149 users' hints, 159 Structure of high speed steel, 168 Sulphur, 33, 108 Tables, air, oil and water hardened steel, 38 alloy steels, properties of, 34 carbon content, 84 carbon steels, 39 case hardening, 97 changes due to quenching, 162 chromium steels, 41 chromium-vanadium steels, 41 colors and temperature, 163 composition of steels, 51, 52 cost of furnaces, 200 effect of size, 118 fuels, comparison of, 191 high-chromium steel, 37 nickel-chromium steels, 40 nickel steels, 39 operating cost of furnaces, 200 production cost of furnaces, 201 S. A. E. steels, 49 screw stock, 39 silico-manganese steels, 41 stock for balls, 62 temperature conversion, 232- 234 tempering temperatures, 158 weight of steel, 235-237 Tank for quenching, 89 dies, 147 Taylor instruments, 215 Temper, colors of, 157 list, Latrobe, 150 of steel, 149 Temperature recorders, 127 tables, 232-234 Temperatures for tempering, 158 Tempering colors on carbon steels, 163 gages, 161 high speed tools, 177 machine, Gleason, 129 round dies, 161 temperatures, 158 theory of, 156 INDEX 245 Tempers of carbon steel, 150 Testing heat treatment, 125 Tests of steel, 16 Test specimens, 23 Theory of tempering, 150 Thermocouple, 204 base metal, 205 cold end, 206 placing, 218 protectors, 227 rare metal, 205 Time for hardening, take, 148 Tool furnace, small, 187 or crucible steel, annealing, 76 steel, cyanide bath for, 133 quenching, 150 Tools, carbon in different, 149 carbon steel, 145 of high speed steel, 173 tempers of various, 150 Transmission gear steel, 59 Treatments for various steels, 92 Troosite, 22, 106 Tubes, calorized, 229 carborundum, 229 Tubes, Chamotte, 22S clay, 229 Marquardt mass, 22S silica, 228 Tungsten, 30-32, 108 steel, 30-32 U Users of steel, hints for, 159 V Vanadium, 28-29, 108 steel, 28-29 W Water annealing, 155 cooled furnace fronts, 197 Weight of steel bars, 235-237 Working instructions for high speed steel, 175 Wrought iron, ix