j
M /o c
3 ao 4o
6O QO 94 IOO
M'/o 100 97 SO 60 -40 2.0 GO
Fig. 406. Diagram showing the structural composition of binary alloys whose component
metals are partially soluble in each other in the solid state.
Figure 405. By comparing it with the fusibility curve of metals entirely insoluble
(Fig. 396) it will be noted that the only differences between them are (1) that the
eutectic line SES' instead of extending over the whole length of the diagram now st < >\ >s
at the points S and S' corresponding respectively to 5 per cent of metal M and to 10
CHAPTER XXV CONSTITUTION OF .METALLIC ALLOYS
425
per cent of metal M', and (2) the introduction of the branches SA and S'B indicates the
changes of solubility of the metals as the alloys cool from the eutectic to atmospheric
temperature. These curves show that at atmospheric temperature M' retains in
solution 3 per cent of 37 and that M retains in solution 6 per cent of M'. LEL' is
the liquidus, LSES'L' the solidus. Clearly, any alloy containing less than 5 per cent
of the metal M or less than 10 per cent of the metal M' solidifies as a solid solution,
the diagram showing the absence of eutectic alloys. In other words, alloys contain-
ing from to 5 per cent of M may be considered as alloys of M' and of a solid solution
of .17' plus 5 per cent of .17, LM' being the liquidus and LS the_sqlidus of such alloys
and their solidification taking place as explained in the case of any two metals form-
ing solid solutions. And, likewise, alloys with less than 10 per cent of M' may be re-
garded as alloys of the metal M and of a solid solution of M plus 10 per cent of M',
their liquidus being represented by L'M and their solidus by US'. For all alloys
containing between 5 and 90 per cent of M the diagram shows that a eutectic alloy is
formed and that the mechanism of the solidification is apparently the same as the one
10 SO 3O +O SO O JO QO SO IOO % Cu
ooo
coo.
700
coo
100
1084-,
962
SolifL soiuiion. A. +
Solid solution, B
o 10 20 30 to so eo 70 ao so too
A torn. / a Cu .
Fig. 407. Fusibility curve of alloys of silver and copper.
(Desch.)
described in the case of alloys of insoluble metals. It should be noted, however, that
the two components of these alloys are no longer the pure metals but two solid solu-
tions, namely, a solution of M' containing 5 per cent of M and a solution of M con-
taining 10 per cent of M', one of these solid solutions, therefore, crystallizing when the
temperature of the alloy reaches any point on the lines LEL' and the eutectic alloy
being made up of a fine conglomerate of these two solid solutions. To clarify let us
consider an allo^ represented by the point R, Figure 405. At N its solidification be-
gins, crystals of a solid solution of M' containing 5 per cent of M being formed. At P
the residual molten mass, having reached the eutectic ratio, crystallizes at a constant
temperature as a fine aggregate of the two solid solutions. Since the mutual solubili-
ties of the metals M and M' decrease, however, as the alloy cools below the eutectic
temperature, it is evident that each crystal must undergo a gradual transformation.
These transformations are indicated by the branches SA and S'B. After the
solidification of the eutectic, all alloys are aggregates of the two solid solutions whose
compositions are represented by the points S and S', that is, in the case under con-
sideration, arbitrarily, M' plus 5 per cent of M and M plus 10 per cent of M'. At atmos-
pheric temperature all alloys are aggregates of two solid solutions whose compositions
correspond to the points A and B, that is in the case considered M' plus 3 per cent of .17
426
CHAPTER XXV CONSTITUTION OF METALLIC ALLOYS
and M plus 6 per cent of .I/'. At any point below the eutectic line, the corresponding
alloy is an aggregate of two solid solutions whose compositions are indicated by the
corresponding points on the branches SA and S'B. At ( '. for instance, in case of alloy R,
the structure is composed of free crystals of solid solution D and of eutectic, the com-
'*&*$*#**
.f>
^^^^^^^-'
Fig. 408. Silver-copper alloy. Copper 15 per cent.
Magnified 600 diameters. Dark constituent is
silver containing a little copper. (Osmond. j
Fig. 409. Silver-copper alloy eutectic.
Copper 28 per cent. Magnified 600
diameters. (Osmond.)
Fig. 410. Silver-copper tilloy. Copper (>."> per cent.
Magnified 000 diameters. Light constituent is
copper containing a little silver. (Osmond.)
ponents of which are solid solution D and solid solution F. In other words, as the alloy
cools from the eutectic line to atmospheric temperature, the composition of its two
constituents shifts respectively from S to .1 and from 8' to R.
The structural composition of alloys whose component metals are partially soluble
when solid may be represented in the usual way as shown in Figure 406. Its interpre-
CHAPTER XXV CONSTITUTION OF METALLIC ALLOYS 427
tation does not call for further elaboration. Between and 3 per cent of M and
between and 6 per cent of M', solid solutions are formed of corresponding composi-
tions. Between 3 and 40 per cent of M, the free solid solution formed is saturated with
.]/. and between 40 and 94 per cent of M it is saturated with M', while the eutectic
is made up of the two saturated solutions. The fusibility curve of silver-copper alloys
is shown in Figure 407 as an example of alloys whose components remain partly solu-
ble in each other after solidification and typical structures of these alloys are given
in Figures 408 to 410.
CHAPTER XXVI
EQUILIBRIUM DIAGRAM OF IRON-CARBON ALLOYS
Fusibility Curve of Iron-Carbon Alloys. Steel and cast iron are essentially alloys
of iron and carbon, and their fusibility curve or equilibrium diagram may be con-
structed as in the case of any binary alloy, namely, by determining the independent
cooling curves of a number of alloys of the series and plotting the evolutions of heat
/Soo _
looo
Percent C O
Percent Fe 3 C O
/.O 1.7 2.0 3.0 4.04.3 JTO 6.O 6.67
A5" 30 45 60 7^ 9O IOO
Fig. 411. Fusibility curve of iron-carbon alloys.
noted against the corresponding temperatures. The resulting curve is shown in the
diagram of Figure 411.
While it is not generally possible for molten iron slightly above its melting-point
to dissolve more than 5 per cent of carbon, the diagram has been constructed so as to
include a percentage of carbon up to 6.67 per cent which corresponds to 100 per cent,
Fe 3 C. That portion of it, however, corresponding to more than 5 per cent of carbon,
has been drawn in dotted lines. The complete equilibrium diagram should include
the evolutions of heat occurring after solidification, known as the critical points,
which have been fully described in these chapters, but they are purposely left out of
the diagram of Fig. 412, it being desired first to confine our attention to the mechanism
428
CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IROX-CARBOX ALLOYS 429
of the? solidification of iron-carbon alloys. In view of the explanation of the meaning
of fusibility curves given in Chapter XXV, it will be evident that iron and carbon al-
loys are partially soluble in each other when solid, that LEU is their liquidus and
LSS' their solidus and that the point E indicates the formation of a eutectic alloy.
As carbon increases from to about 1.70 per cent, the alloys solidify as solid solutions
of corresponding carbon content, LA being the liquidus and LS the solidus. These
solid solutions considered as microscopical constituents are called austenite. The so-
lidification of alloys containing between 1.7 and 4.3 per cent carbon begins when their
temperature reaches the line LE, crystals of a solid solution containing 1.70 per cent
carbon (sometimes called saturated austenite), being then formed which keep on
growing until the line SS', temperature 1130 deg., is reached when, clearly, a eutectic
/~/ypo -e ui~e eft c a / ' /ot/s
Hyper- eufecfic
/oo
Hypo .
f-/yper- o u i~e c t' rc
^-eutecfic A
V P'ro-evfect'i c
Safurafed /
V Cement/ fe
c
Ausfen ife /f[
.0 75
A
" -N.
/
5
/!'
o
A\\ufm^'f*f ^
|.
Sol lu \SOIUi tOD
/\\\ \ *- t// e
i r\
O ,-
(A sf& YeJ
A^afurafed
Ausfenite \
o 5o
A + Cemer
,f/y e j \"
~~Q
t
K
X
'
K
/
\
S5
i
V
2s
y
y'
Ik
o
k
%C o '/.o >.o
so 4.o
^O 6.O 6.67
/o/~ 3 C O A5~ 3O
45 60 75 90 too
Fig. 412. Structural composition of iron-carbon alloys immediately after their solidification.
is formed composed of that solid solution and of another constituent. The nature of
the other constituent present in the eutectic alloy formed during the solidification of
iron-carbon alloys has been in dispute. It seems at first natural to infer that elemental
carbon, i.e. graphite, is that constituent, in which case the eutectic alloy would be
made up of minute crystalline particles alternately of saturated austenite and of
graphite. Many evidences, however, point to carbon being dissolved in molten iron
as the carbide Fe 3 C (cementite) and to its always solidifying as Fe 3 C, although, as
later explained, it may break up into iron and graphite (Fe 3 C = 3Fe+C) immediately
after its solidification. If this hypothesis be correct, it follows that the eutectic alloy
must be a mechanical mixture of minute particles of saturated austenite and of FeaC.
It would seem at first as if the microscopical examination of alloys of suitable compo-
sitions should readily reveal the nature of the eutectic alloy. It will soon be seen,
however, that both cementite and graphite are generally found in solidified eutectifer-
ous alloys, the microscopical test leaving us in doubt as to which of the two constitu-
430 CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IROX-CARBON ALLOYS
ents formed first. In the author's opinion it seems more probable that when an iron-
carbon alloy containing more than some 1.7 per cent carbon solidifies, a eutectic of
saturated austenite and of cementite is always produced, or in other words, that in
the diagram of Figure 411 the curve L' E indicates the crystallization of cementite and
not of graphite. The opposite view will be considered later. Let us now follow the
solidification of four typical alloys, namely, R, /(", K" ', R'", containing respectively
1 per cent, 3 per cent, 4.3 per cent, and 4.8 per cent of carbon, the first two being,
therefore, hypo-eutectic alloys, the third the eutectic alloy, and the fourth a hyper-
eutectic alloy. As the alloy R cools, it begins to solidify at Af through the formation
of crystals of a solid solution the composition of which is represented by the point T
on the solidus. On cooling from M to N these crystals grow through successive addi-
tions of crystalline matter, the composition of which varies from T to N while the
composition of the molten bath shifts from M to U, the last drop solidifying having
the composition U. As soon as the crystalline matter is deposited, however, at least if
time be given, diffusion takes place through each crystal so that finally they are chem-
ically homogeneous and of composition N , the completely solidified metal being com-
posed of homogeneous crystalline grains of austenite containing one per cent carbon.
At any temperature V between the solidus and the liquidus the crystals in equilib-
rium with the molten metal must have the composition Q. It may at least be con-
ceived that if the cooling through and below the solidification period be rapid, the
crystalline grains of austenite will not be chemically homogeneous, complete diffusion
having been prevented;
In the case of an alloy whose composition is represented by the point R' in the
diagram, it begins to solidify at M' (some 1230 degrees ('.), when crystals of iron
containing 1.70 per cent of carbon (saturated austenite) begin to form, the composition
of the molten metal meanwhile shifting from M' to E. At 0', temperature 1130, the
residual molten mass has reached the eutectic composition and now solidifies at a
constant temperature, namely, the eutectic temperature, the completely solid metal
being made up of crystalline grains of saturated austenite surrounded by a eutectic alloy
composed of minute crystals of saturated austenite and minute crystals of cementite.
The alloy K" has the eutectic composition (4.3 per cent carbon). It remains
liquid until its temperature falls to 1130 deg. C. when it solidifies at a constant
temperature after the fashion of eutectic alloys.
The alloy R'" contains more carbon than the eutectic alloy. On reaching its
solidification point M'" crystals of cementite begin to form, increasing in size as the
metal cools from M'" to ()'" while the composition of the bath shifts from M'" to E.
At 0'" the residual molten mass having now the composition of the eutectic alloy,
freezes at a constant temperature, the completely solidified alloy being made up of
crystals of cementite embedded in a ground mass consisting of the eutectic alloy.
Structural Composition of Iron-Carbon Alloys Immediately after Solidification. -
The structural composition of iron-carbon alloys immediately after their solidification,
assuming that Fe 3 C and not graphite forms, may be represented in the usual way by
the diagram of Figure 412. The diagram clearly shows (1) that alloys containing less
than 1.70 per cent of carbon are made up wholly of solid solutions, (2) that alloys
containing between 1.70 and 4.3 per cent carbon are made up of decreasing propor-
tions of saturated austenite and increasing proportions of eutectic, (3) that alloys
containing exactly 4.3 per cent of carbon are composed entirely of eutectic, and (4) that
alloys containing more than 4.3 per cent carbon contain an increasing amount of free
CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IROX-CARBON ALLOYS 431
cementito, and decreasing amount of euteetic the latter disappearing altogether when
the metal contains 6.67 per cent carbon. 1
A modified form of the structural composition diagram may profitably be combined
/Soo
o
I
o
loo
7-5
SO
2-5
Auste
D
O
C F> H
2 3 <4
f~'erceni~ Carbon.
F"
6.67
Fig. 413. Fusibility curve and structural composition diagram of iron-carbon alloys.
with the equilibrium diagram as shown in Figure 413. Its interpretation should be
obvious. The area A BCD represents the structural composition of all alloys contain-
ing less than 1.7 per cent of carbon, and shows that they are made up of 100 per cent
1 Howe questions the existence below solidification of pro-eutectic cementite on the ground that it
graphit i/.cs as soon as formed unless the cooling be extremely rapid or considerable manganese present.
432 CHAPTKK XXVI EQUILIBRIUM DIAGRAM OF IRON-CARBON ALLOYS
of austenite. By dividing this area by the line AC, however, it is further shown graphi-
cally that the composition of the austenite of these alloys varies, and that they may he
considered as being made up of ABC saturated austenite diluted by ADC pure iron,
clearly indicating that with carbon the alloy is entirely made up of iron and with
1.7 per cent carbon entirely of saturated austenite. The area BCH represents the
proportion of free (pro-eutectic) saturated austenite formed during the solidification
of any alloy containing between 1.70 and 4.3 per cent carbon. The area BEFH rep-
resents the proportion of eutectic present in any alloy containing more than 1.7 per
cent of carbon. By dividing this area in two portions, moreover, by means of the line
BF we show graphically the relative proportions of saturated austenite and of cenien-
tite in the eutectic. Finally, the area EOF indicates the percentage of pro-eutectic
Temperature
iv> oi * <
<
c
\X x
^ NX ^O /
^P
^ //
\ V-* W
v y
\ *^ ~9"i /**
\ o** ^ ""*^ ("O/
\ ~~^? ? ' /
Z'
IIQO
IOO6
Au $ ~/~e ni te -& ropht f~& eui~e ofic, sol if il ' e eu1~ec,1~i c. sol id i fie\5.
i.o
IS
2.O
30
J.O
4-S
4.Q
GO
SO
75
GO
9O
667
/OO
Fig. 415. Combined graphite-cementite fusibility curves of iron-carbon alloys.
In the first instance the two following equations
(1) A + E = 100
100
100
will give the values of A and E for any known carbon content (C) while in the latter
case the equations
(1) Cm + E = 100
100
100
will likewise give the values of Cm and E.
An alloy, for instance, containing 3 per cent of carbon will be found to contain 50
per cent of eutectic and 50 per cent of saturated austenite, while an alloy with 5 per
cent carbon is composed of 70.5 per cent of eutectic and 29.5 per cent free cementite.
434 CHAPTER XXVI KQI'ILIBHIUM DIAGRAM OF IRON-CARBON ALLOYS
Iron-Graphite Fusibility Curve. It has already been mentioned that some
writers claim that graphite instead of ceinentite may, and if time be given docs, form
on solidification; in other words, that the eutectic alloy may be' composed of saturated
austenite and graphite, and that free graphite may separate during the solidification
of alloys containing more than 4.3 per cent carbon. The diagram interpreting this
assumption which may be called the iron-graphite fusibility curve is shown in Figure
414. It will be seen to be similar to the iron-cementite diagram (Fig. 411).
Combined Graphite-Cementite Diagram. Recognizing the possibility of the
formation of a graphite-austenite eutectic and of a cementite-austemte eutectic ac-
cording to the rate of cooling, some writers, notably ('harpy and Crenel, Heyn, and
Benedicks, recommend the use of double solidification curves in the equilibrium dia-
gram of iron-carbon alloys. These double curves are shown in Figure 415, the dotted
lines referring to the austenite-graphite system. It will be noted that free graphite
and the graphite-austenite eutectic form respectively at temperatures slightly higher
than those at which free ceinentite and the cementite-austenite eutectic form, the
solidification of the latter constituents being regarded as due to surfusion or under-
cooling. It is accordingly believed that only the iron-graphite system is stable, the
iron-cementite system being "metastable." Our reasons for believing that graphite
and not cementite is the final condition to be assumed by carbon are based on repeated
and concordant observations that any condition promoting stable equilibrium results
in the transportation of cementite into graphite as, for instance, very slow cooling
during and below solidification or long exposure of cementite (as in the manufacture
of malleable cast-iron castings) to a high temperature, while on the contrary, treat-
ments opposing equilibrium, such as quick cooling, always result in the formation or
retention of cementite. Roozeboom, when he first took up the study of the iron-
carbon diagram, believed that cementite was the final stable condition of carbon, any
graphite having formed during solidification combining with iron at some 1000 degrees
C. to form cementite. The error of this view soon became apparent, however, to
Roozeboom himself.
Graphitizing of Cementite. Although recognizing the fact that graphite and not
cementite must be the final condition assumed by carbon, the author believes with
some other observers that graphite never forms directly as iron-carbon alloys solidify,
its occurrence always resulting from the breaking up of cementite according to the
reaction
Fe 3 C = 3Fe + C
from which it would follow that the iron-graphite fusibility curve need not be in-
cluded in the equilibrium diagram. Even those who believe in the possibility of the
direct formation of graphite do not deny that ceinentite is the constituent which
generally forms first on solidification; they state that the separation of graphite from
molten iron is possible only in the case of very slow cooling. As a matter of fact, how-
ever, they offer no conclusive evidences that such separation ever takes place. From
the formation of "kish," that is, of graphite floating on the surface of a ladleful of
molten cast iron, it does not follow that such graphite formation was not preceded by
the formation of cementite. If, on very slow cooling, graphite separated directly from
molten iron, the bulk of it at least should rise to the top of the molten bath and the
solidified mass should be found much richer in graphite near its surface than at some
distance from it. The author does not understand such heterogeneity in the dis-
tribution of graphitic carbon to be observed in the case of gray cast-iron cast-
CHAPTKH XXVI EQUILIBRIUM DIAGRAM OF 1RON-CARBOX ALLOYS 435
ings. 1 On the contrary, on the assumption that graphite results from the breaking up of
cementite soon after its solidification, it is readily understood why, in spite of their very
great difference in specific gravity, iron and graphite are found uniformly distributed in.
the various parts of castings. The microscopical examination of the structure of very
.slowly cooled castings does not reveal the existence of a graphite-austenite eutectic.
That cementite is unstable, being readily converted into iron and graphitic carbon,
is also generally admitted. It is upon this instability of cementite that the important
industrial operation of converting white cast-iron castings into graphitic malleable
castings is based. And there is abundant evidence that the higher_the temperature,
the more readily is cementite dissociated, from which it follows that the higher the
temperature at which cementite forms the more readily will it be converted into
graphitic carbon. Bearing this in mind, and with the assistance of the diagram of
Figure 3, let us look more closely into the graphitizing of cementite. The diagram
shows clearly that, during the solidification of alloys containing more than 1.70 per
cent of carbon, (1) some cementite forms as pro-eutectic cementite if the metal con-
tains more than 4.3 per cent carbon, (2) some cementite forms as eutectic cementite in
all alloys, (3) some cementite remains dissolved in the eutectic-austenite of all alloys,
and (4) some cementite remains dissolved in the free austenite of alloys containing less
than 4.3 per cent carbon. Considering first the free cementite, that is, the pro-eutectic
and the eutectic cementite, it is evident that the former is formed at a higher tempera-
ture, and that the more carbon in the alloy the higher the temperature at which it
begins to form. It seems safe to infer, therefore, that pro-eutectic cementite will break
up into graphite and ferrite more readily than eutectic cementite, this being consistent
with the well-known fact that hyper-eutectic alloys are generally rich in graphite even
after relatively quick cooling. The presence of pro-eutectic cementite may also pro-
mote the formation of graphitic carbon because once this graphitizing process is
started, it is likely to extend, if time be given, to the bulk of the cementite, first the eu-
tectic cementite and later the austenite-cementite undergoing the change. Alloys con-
taining less than 4.3 per cent carbon and consequently free from pro-eutectic cementite
should not become graphitic as readily because of the lower temperature at which
eutectic-cementite forms. If a large proportion of cementite be formed, however,
that is, if the alloys contain more than 3 or 3.5 per cent of carbon, a certain amount
of graphitizing is readily induced through slow cooling. With decreasing carbon
the breaking up of cementite becomes progressively more difficult until, in alloys con-
taining less than 1.7 per cent carbon (the steel series), and, therefore free from eutectic
cementite, graphitic carbon is very seldom formed.
It should be borne in mind that while those alloys which contain but a small pro-
portion of carbon cannot be made graphitic, when a large proportion of carbon is
present, the graphitizing once started may be made to include the totality of the
cementite, thus explaining the freedom of steel from graphite and the freedom of
some cast irons from cementite.
The foregoing remarks apply to pure iron-carbon alloys, the influence of the
elements generally present in commercial products having been purposely ignored.
When dealing with commercial steel and cast iron, the well-known influence of silicon
in promoting the formation of graphitic carbon should be remembered as well as the
opposite 1 influence of sulphur and manganese 1 . Because of the presence of a notable
1 Howe reports the segregation of graphite in the upper part of lash-bearing east iron, but this
is readily explained on the ground that such irons must be liyper-eutectic in composition and that
the pro-eutectic cementite beginning to graphitize while the iron is still partially liquid shows a
tendency To rise to the top, hence indeed the formation of kish.
Fig. 417. Magnified 7.~>l> diameters.
Fig. 41(1. Magnified ">() dimnetora.
\^. 11'.). Magnified 760 diameteis.
Fig. 41S. Magnified ">" diameters.
Fi K . IL>CI. - .M:igmlu:d."iOdianii-i.T.s.' Fig. 421. Magnified 760 diametew.
Figs 41(i and 417. Iron-carbon alloy. Hypo-eutcctic. Structure immediately after solidification. Dark crystallite of
nturated aiutenitc in a matrix of aurtenlte-oemwitiU ruti-ctic. Figs. 41S and 41!). - Iron-carbon alloy. Aiisir,,i:,.-
ccnii'iititi. rutoctic. Figs. 420 and 421. Ir.m-<-:trl>.m alloy. Hyper-cuteotic. Strui'ture iinnifdiati'ly after snlidifi-
cation. Nil-dies of fcinc'iititf in a matrix of ailsti'iiiti-cc'inc'iititc cutoctk-. (QorODB.)
436
CHAPTER XXVI EQI'ILIBKH M DIAGRAM OF IKOX-CARbOX ALLOYS 437
proportion of silicon, commercial cast irons after slow cooling are necessarily more
graphitic than pure alloys of same carbon content.
Structure of Iron-Carbon Alloys Immediately after Solidification. If the alloy
contains less than some 1.70 per cent carbon it is made up after complete solidification
of crystalline grains of austenite. It has been explained, however, that in the absence
of manganese or other ''retarding" elements it is not possible to prevent, even through
very rapid cooling, the transformation of some of the austenite at least into martensite.
The polyhedric structure of austenite has been illustrated in these lessons in the case
of special steels (manganese and nickel steels) and it is now welLunderstood that the
r
6.67
Fig. 4122. Equilibrium diagram of iron-carbon alloys.
frequent network structures of slowly cooled steel are due to the existence of poly-
hedral austenitic structures above their critical range.
If the alloy contains from 1.70 to 4.3 per cent carbon it is made up, after solidifi-
cation, of crystals of saturated austenite and of eutectic alloy. This is well shown
after (kurens in Figure 416, in which the dark "pine tree" crystals consist of saturated
.Mistenite, while the ground mass is the cementite-austenite eutectic. 1 In Figure 417
the same structure is shown more highly magnified. If the alloy contains exactly 4 3
per cent carbon, it consists wholly of eutectic as shown under different magnifications
m Figures 418 and 419. It has been seen that, theoretically, this eutectic contains
47.7 per cent, of saturated austenite (the dark constituent), and 52.3 per cent of cem-
entite. Alloys containing more than 4.3 per cent carbon consist after solidification
of free cementite in the form of needles embedded in a eutectic matrix as shown in
Figures 420 and 421.
It should be noted that the dark constituent occurring in these structures and
described as saturated austenite may not be absolutely unaltered austenite because of
1 Wiist has suggested the name of " Ledcburite" for this eutectic in honor of the late well-known
German metallurgist A. Ledebur.
438 CHAPTER XXVI KQl'ILIBRIUM DIAGRAM OF IROX-CARIiON ALLOYS
CHAPTER XXVI I'XjriLIBKH'M DIACKA.M OF JHOX-CARBOX ALLOYS 439
the difficulty of completely preventing the transformation of that constituent even
in the presence of a large amount of carbon and by very sudden cooling. If the aus-
tenite has undergone some transformation, however, so that it contains some mar-
tensite and even troostite those transformations must have taken place in situ and the
structures reproduced in Figures 6 to 11 must represent accurately the structural
aspect of the corresponding alloys after solidification.
Complete Equilibrium Diagram. In the foregoing pages only the solidification
curves of iron-carbon alloys have been considered and the probable mechanism of
their freezing explained. Their equilibrium diagram, however, jnust include all heat
evolutions observed on cooling from the liquid condition to atmospheric temperature;
in other words, the thermal critic ;1 points fully described in previous chapters arc
part of the complete equilibrium diagram as indicated in Figure 422.
Since the meaning of every curve of this diagram has been discussed, it only re-
mains to inquire into any possible structural or other changes taking place after
solidification and before the alloys reach their respective thermal critical point or
points, that is, while they cool from the solidus LSS' to the eutectoid line CDF. The
changes which do or may take place as the alloys cool in this range are clearly stated
in Figure 42:>. In this diagram the most likely significance of every curve is indicated
as well as the nature of all structural transformations, and of all possible resulting
structures after complete cooling. The author believes that it embodies those infer-
ences best supported by analogy and by experimental evidences. Although neces-
sarily involving some repetition, a methodical examination of the various parts of
this complete diagram seems advisable, as it will permit a recapitulation of the various
matters previously discussed.
Let us consider (1) the solidification of iron-carbon alloys, (2) their cooling from
the solidus LtfES' to the eutectoid temperature CDF, and (3) their cooling through
the eutectoid temperature and their final structures.
According to the mechanism of their solidification iron-carbon alloys are divided
into three classes, namely, (1) alloys containing less than 1.70 per cent of carbon, (2)
alloys containing between 1.70 and 4.3 per cent carbon, and (3) alloys containing
more than 4.3 per cent of carbon. Alloys containing less than 1.70 per cent of carbon
and including, therefore, all the steels of commerce solidify as solid solutions of the
carbide Fe. ( ( ' (cementite) in gamma iron, these solutions being known as austenite.
LA is the liquidus and LS the solidus of these alloys. Alloys containing between 1.70
and 4.3 per cent of carbon solidify through the formation of crystals of saturated
austenite at gradually decreasing temperatures and through the final solidification,
at the euteetic temperature, of the residual molten metal necessarily of eutectic com-
position. Alloys containing more than 4.3 per cent of carbon solidify through the
formation of cementite crystals at gradually decreasing temperatures, and through to
final solidification, at the eutectic temperature, of the residual molten metal necessarily
of eutectic composition.
In cooling below their solidus, LS, alloys with less than 1.70 per cent carbon undergo
no change until they reach their thermal critical points Ar 3 , Ar 3 .2, Ar 3 . 2 .i or Ar cm as
the case may be, when, if they contain less than some 0.85 per cent of carbon (hypo-
eutectoid steels), some iron is set free and converted into beta iron, while if they
contain more carbon (hyper-eutectoid steels), cementite is liberated. In either case
when the eutectoid temperature is reached the residual austenite, now of eutectoid
composition (0.85 per cent carbon), is converted into pearlite.
440 CHAPTER XXVI EQUILIBRIUM DIACHAM OF 1ROX-CARBOX ALLOYS
ISOO, 2 ^ 6_
F'ro - e u Te c ti c
te \ Cerri entile
Structural
corn-position
i rrtrn ec//a/e /y
ofter-
Solid if i cat I on
SfrucTurol
com po-s it/On
/mm ed i a te/y
Structural
compos it ion
/6e /ow
2 4 6 6.57
C-arbon /o
Fig. 424. Equilibrium and struct unil composition cli:is>':uii of iron-carbon allovs.
CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IRON-CARBON ALLOYS 441
After solidification, alloys containing between 1.70 and 4.3 per cent carbon are
aggregates of saturated austenite (austenite containing 1.70 per cent C or 25.5 per
cent cement it i 1 ) and of cenientite-austenite eutectic. On cooling below their solidus,
cementite (pro-eutectoid cementite) is liberated both from the free and from the
eutectic-austenite, while if the cooling be sufficiently slow both the eutectic and pro-
eutectoid cementite may be partly or wholly dissociated into graphite and iron (ferrite).
Indeed, the graphitizing may even include the eutectoid cementite, in which case the
alloy is made up solely of ferrite and graphite.
Alloys containing more than 4.3 per cent of carbon are, immediately after solidi-
fication, aggregates of cementite (pro-eutectic cementite) and of cementite-austenite
eutectic. On slow cooling below their solidus, cementite (pro-eutectoid cementite) is
liberated from the eutectic austenite while the pro-eutectic, eutectic, and pro-eutectoid
Fig. 425. The author's early equilibrium diagram (1896).
cementite may be partly or wholly dissociated into graphite and ferrite, in some ex-
treme cases the eutectoid cementite even being graphitized.
On cooling through the eutectoid temperature, any remaining austenite is bodily
converted into pearlite.
The above consideration clearly shows that in alloys containing more than some
1.70 per cent carbon four types of structure may be formed according to the rate of
cooling below the solidus:
(I) Cementite plus pearlite, the structure of white cast iron, readily produced by
quick cooling and representing a metastable equilibrium. (II) Ferrite and graphite,
an extreme case, possible only after very slow cooling and in the presence of much
silicon, little manganese, and sulphur, and representing stable equilibrium. (Ill) Cem-
ent ite plus pearlite and graphite, the structure of gray cast iron with hyper-eutectoid
matrix, resulting from slow cooling, promoted by the presence of silicon and opposed
by sulphur and manganese. (IV) Pearlite, ferrite, and graphite, the structure of gray
cast iron with hypo-eutectoid matrix, produced because of slower cooling or because
of the presence of more silicon or of less sulphur and manganese.
442 CHAPTKH XXVI EQUILIBRIUM DIAGRAM OF 1RON-CAHHOX ALLOYS
It will be explained in the next chapter that, according to the phase rule, only two
components may be present in a binary alloy in a state of equilibrium from which
it follows that gray cast irons, since they contain besides iron both cementite and
graphite, are out of equilibrium. One of the components must disappear if the alloy
is to assume equilibrium. Cementite is undoubtedly that component as proven by
the malleablizing of cast iron when cementite is readily dissociated into graphite and
ferrite on prolonged heating to a high temperature.
In Figure 424 the complete equilibrium diagram is shown combined with three
constitutional diagrams showing graphically the structural composition of iroii-car-
bon alloys (1) immediately after their solidification, (2) immediately before the eutec-
toid temperature, and (3) below the eutectoid temperature, on the assumption that
no graphitic carbon is formed. The structural changes taking place while the alloys
1.500-
1.400"
* 1.300-
S 1.200-
^1,100-
it l '
1
2
i
4
Fig. 426. Roberts-Austen's first equilibrium diagram (1897).
cool below their solidus down to the eutectoid temperature are, in this way, clearly
depicted. The following facts, for instance, are graphically shown, (1) the pro-eutectic
cementite formed during the solidification of hyper-eutectic alloys and the eutectic
cementite present in all alloys containing more than 1.70 per cent carbon remain un-
changed as the alloy cools to atmospheric temperature, (2) the free saturated austenite
of hypo-eutectic alloys, as well as the eutectic-austenite, are converted into eutectoid
austenite through the liberation of cementite (pro-eutectoid cementite), the area
EDH representing the cementite thus set free, and (3) in hypo-eutectoid alloys iron
is set free as shown by the area FJG. The lower diagram shows that, in cooling
through the eutectoid temperature, the remaining austenite, now necessarily of
eutectoid composition, and sometimes called hardenite is converted into pearlite.
Taking, for instance, the metal whose composition and temperature are represented
by the point R, its transformations and final structure are clearly shown. At M it
begins to solidify through the formation of crystals of saturated austenite; from M to
N the austenite crystals continue to grow, the percentage of free austenite present in
the solidified metal being represented by the distance OP; at N the residual bath
CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IROX-CARBOX ALLOYS 443
solidifies as a eutectic alloy, the percentage of which is proportional to the distance
KO; this eutectic contains KL = PQ = TU per cent of cementito and LO per cent
of saturated austenite; LI' is the total amount of austenite in the alloy; after solidifi-
cation in cooling from N to K, pro-eutectoid cementite is liberated both from the
free and from the eutectic-austenite, Q8 representing the percentage of cemeiitite
finally expelled; on reaching the point K, the remaining austenite, ST, is of eutectoid
composition, when it is sometimes called hardenite, and in cooling through K this
austenite is converted into pearlite, the metal being finally made up of TU per cent
of eutectic cementite, UV per cent of pro-eutectoid cementite, and VX per cent of
pearlite, the latter containing VW per cent of cementite, and WX per cent of ferrite,
or of TV per cent of free cementite and VX per cent of pearlite, or again of TW
per cent of total cementite and WX per cent of ferrite.
Historical. In view of the scientific and practical importance of the equilibrium
3-0 &Z
CARBON PER CENT
* *Z tti.fi s ft S *
l-'ig. 427. Roberts-Austen's second equilibrium diagram (1899).
diagram of iron-carbon alloys, a brief historical sketch of its evolution should be of
interest to the reader. The first diagram was published by the author in 1896. 1 It is
reproduced in Figure 425. It will be noted that, although the diagram includes only
the thermal critical points, it is otherwise substantially accurate. In describing it
the author wrote in part:
"Figure 1 shows graphically the position of the critical points in cooling steels of
various carbons. The width of the black lines does not refer to the intensity of the
retardations, but only indicates the range of temperature which they cover. For
instance, it shows that the single retardation of high carbon steel begins at about
680 deg. C. and ends at about 640 deg. C. The maximum evolution of heat lies some-
where between these limits, but not necessarily in the middle.
' This graphical representation was obtained by plotting the results of the investi-
gations of Osmond, Howe, Roberts-Austen, Arnold, and the writer; and, with one or
two exceptions all their figures fall very nearly within the limits here indicated."
1 "The Microstructure of Steel and the Current Theories of Hardening," ALBERT SAUVEDK,
Transactions American Institute of Mining Engineers. 1896, p. 867.
444 CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IRON-CAKBOX ALLOYS
It is from this modest beginning that the present diagram was evolved. 1
In 1897 Roberts-Austen published in his fourth report of the Alloys Research Com-
mittee of the Institution of Mechanical Engineers the diagram reproduced in Fig. 426.
Two years later, in 1899, the diagram shown in Fig. 427 was published by Roberts-
Austen and Stansfield in the fifth report of the Alloys Research Committee. Some of
the conspicuous features of this diagram should be noted. The solidification point of
pure iron was indicated to be 1600 degrees C. whereas we know now that it is nearly
1500 deg. No attempt had been made yet at ascertaining the end of the solidification,
that is, the solidus, of alloys forming solid solutions; the formation of a eutectic on
solidification was indicated as taking place in alloys containing more than one per cent
carbon; graphite was supposed to crystallize during the solidification of alloys con-
'too'
soo
000*
Warte isite
Fsrr'le*
PerUff
3L-
-P*
***
Ma
Ci 'rbon Per 3
Wart, visit*
~!ra/t hike
nfrJ-s
T.is
=r2
Liquid.
yCrafi/iite
F'
a
&
R
Fig. 428. Roozeboom's equilibrium diagram (1900).
taming more than 4.3 per cent carbon, there being in the diagram no indications of pos-
sible formation of cementite; the eutectic alloy was assumed to be a graphite-iron eu-
tectic ; critical points occurring below the eutectoid temperature were represented in the
diagram and marked "hydrogen points" (see Chapter X, "Minor Critical Points");
the Ar cm curve was arbitrarily extended to yield a V-shaped curve. Roberts- Austen
mentioned the formation of a solid solution, free in hypo-eutectic steels, and as a con-
stituent of the eutectic in alloys of eutectic composition, and he ascribed the presence
of free cementite in cast iron to the liberation of that constituent from solid solution.
In 1900 Roozeboom took up the study of Roberts-Austen's diagram, and applying
to it the teachings of the phase rule published the diagram of Fig. 428 as a probably
accurate representation of the solidification mechanism of iron-carbon alloys and of
the structural transformations taking place after solidification. In this diagram, the
line 6a, that is, the solidus of alloys forming solid solutions, is for the first time indicated ;
1 Since these remarks were written Prof. H. M. Howe has expressed the opinion that credit for
the first equilibrium diagram is due to Rcinhard Mannosmann.
CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IROX-CARBOX ALLOYS 445
1500
X?
5
X
I40O
X
S
2
1300
X
1200
1
kl
5 "00
f-
z
) 10 '
li
ft
D
<
Jj 900
I
kl
H
^
800
CARBON PER CENT
Tig. 429. Carpenter's and Kcrlinij's equilibrium diagram (190-1).
446 CHAPTER XXVI EQUILIHUH M D1.U1KAM OF IRON-CARBON ALLOYS
the word martensite is used instead of austenite to denote the solid solution of iron
and carbon; free graphite is assumed to form during the solidification of alloys con-
taining more than 4.3 per cent carbon and the constituents of the eutectic alloy are
supposed to be martensite (solid solution) and graphite. The Ar ( . m curve of hyper-
eutectoid steels is arbitrarily extended as an horizontal line starting from E (1.75 per
cent carbon and 1000 deg. C.) and extending to the end of the diagram. Roox,eboom
argued that, while graphite formed on solidification in all alloys containing more than
2 per cent carbon, this graphite at 1000 deg. (line EF) recombined with iron to yield
cementite so that, finally, alloys in equilibrium would contain only ferrite and cementite,
thus conforming to the phase rule which forbids the presence of more than two com-
ponents in binary alloys. It has since been conclusively shown that Roozeboom was
in error, that while the ferrite-cementite system is in equilibrium according to the
TEMPER
ATURE
1500'
1400
1300
1100
IOOO
900
600
700
600
500
IF
A
^
-^s
-^
Li
au
D
\
S LI
^\
3UIC
^^
^^^
A
)
4\
QtHO
ENTI'
M *;
& M
\ <
XEC
RSI
ALS
"^
Ss
9*'
r*r\
CEM
YtT
M
IXE
>
gr
__.
- _
__ -
^
s .
"'%'
....
r-
'E"
1
r>
f 11
CR\
'STA
V
'/
1
1
1
U
' /
' h
IXE
) CR
YSTfi
LS
E'
JTE
:TIC
&
\
1
& E
r" TE
:TIC
C
;MEr
TITE
CRY
STAL^
-^
'E
t
^t
PER
ITE
p
EAR
LITE
& c
EME
NTI
re
PEAR
LITE
Pt
/? CA
wr
?Aff6
ON
ION
Fe
r f j -f 5 6 CEM
-TIT
Fig. 430. Benedicks' double equilibrium diagram.
phase rule, it is in metastable equilibrium, the ferrite-graphite system being the only
stable one. The hypothetical horizontal line EF is now consequently omitted from
the equilibrium diagram, and the Ar ( . m curve made to join the eutectic line at its
origin (a).
In 1904 Carpenter and Keeling made a series of very careful experiments in order
to ascertain the evolutions of heat taking place in cooling pure iron-carbon alloys from
the liquid state to atmospheric temperature. By plotting their results, the equilibrium
diagram reproduced in Figure 429 was obtained. The solidification of pure iron is
shown to take place at 1500 deg. C. The curves arc otherwise identical to those of
Roozeboom, the horizontal line EF having been introduced. The faint evolutions of
heat occurring in the vicinity of u'OO deg. ( '. already discovered by Roberts-Austen
and ascribed by him to the presence of hydrogen, were also observed by Carpenter
and Keeling, as well as some faint evolutions in the vicinity of 775 deg., the meaning
of which remains uncertain.
CHAPTER XXVI EQUILIBKITM DI.UIKAM OF IROX-CARBOX ALLOYS 447
When it became apparent that graphite and not cementite must he the final stable
form of carbon, several authorities argued that two equilibrium conditions could exist
according to the rate of cooling during solidification, one of them stable, the other
metiistable, and that this should be indicated in the diagram. This view was presented
notably by ('harpy and Grenet, by Benedicks and by Heyn. The double diagram
advocated by them is represented in Figure 430. The solidification of free cementite
and of the cementite-austenite eutectic being assumed to be due to the well-known
phenomenon of surfusion or undercooling, the corresponding curves are arbitrarily
outlined at temperatures slightly lower than those pertaining to the formation of free
500-
a 1
Carbon, per Cent,.
Fig. 431. Rosenli.-iin's equilibrium diagram (1911).
graphite and of graphite-austenite eutectic. The author has already shown why, in
his opinion, the graphite curves should bo left out. The view that cementite always
forms during the solidification of iron-carbon alloys but that being unstable it is
readily dissociated into ferrite and graphite, seems to be better supported by experi-
mental evidences and more consistent with practical facts.
Rosenhain has recently plotted the experimental results of Carpenter and Keel-
ing, of Gutowsky and of himself, obtaining the diagram reproduced in Figure 431. He
considers Gutowsky's results in regard to the form of the solidus curve of alloys form-
ing solid solutions as more accurate than those previously published, arid he incorpo-
rates them in the diagram as shown in Fig. 431, the solidus line being rounded instead
of straight as heretofore represented. In justification of his course, Rosenhain writes :
" We have now to consider the curved portion of the 'solidus,' the line AD. This
448 CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IROX-CARBOX ALLOYS
represents the temperatures at which the alloys have just completed their freezing
process, that is, have just become completely solid, or, conversely, it represents the
temperature of incipient fusion on heating. In the earlier investigations, and even in
those of Messrs. Carpenter and Keeling, these temperatures were obtained by esti-
mating the point on each of the cooling-curves where the heat-evolution due to solidi-
fication came to an end. Unfortunately, the end of a heat-evolution is never sharply
indicated on the curves, so that this estimation was admittedly vague. Quite recently
that determination has been repeated, and with considerable greater accuracy, lie-
cause a very much more satisfactory method was available . . .
"The method of determining the 'solidus' was to take small pieces of steel, of
known composition, heat them, and suddenly cool them from successively higher
temperatures; afterward each specimen was examined by means of the microscope.
IfiOO
A
^
*^*
1200
2
f
\3
+ liquid
^
liquid
^
gra.
phite +
iquid
N,
-A
^
~v5--'^
D
9
^*^
r+grap
TitC
1145-^
F
H 7
El
H
1095"/
G
,915
/ J
tFe.C
o
Fe c C
f grap!
ite
\78S
I
CO
R
^800
T
K
M
or-tt \
1
r
+ F<
: 3 C
X 725"
*
Fe 3 C -
graphit
e
S
a
+ Fe,C
S S 1
,615
>
W
600
V
u
o
^y ^. jTgo
C
400
Percent
carbon
N a
X &
123
4 567891
* Fig. 432. Upton's equilibrium diagram.
It is easy, as the photographs show, to determine what is the particular point at which
you have reached a temperature where there was a small quantity of liquid metal
present at the moment of quenching."
Upton's Diagram. The rather revolutionary diagram shown in Figure 432 has
been proposed by G. B. Upton. He considers it more satisfactory than the double
diagram, as it does away with the necessary conception of a metastable and a stable
equilibrium at nearly the same temperature. Upton argues that cementite decom-
poses above 800 deg. C. into graphite and iron, but that even after prolonged an-
nealing some 3.5 per cent carbon remains combined from which it is inferred that the
carbide Fe 6 C forms (carbon 3.46 per cent) stable in the region LEFK in the dia-
gram although he adds that it might be a solid solution containing that amount of
carbon which forms at about 800 deg. Fe 6 C is claimed to be converted into Fe 3 C thus
accounting for the evolutions of heat in this region reported by Carpenter and Keel-
ing. At about 600 deg. according to the diagram Fe 3 C is converted into Fe = C thus
explaining the evolutions of heat detected at that temperature by many observers.
It is very difficult to accept the hypothesis that graphite is not the stable condition of
CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IRON-CARBON ALLOYS 449
carbon in the area LEHR and that Fe2C and not Fe 3 C is the condition of the carbon
remaining combined after complete slow cooling. The existence of both FeeC and
Fe 2 C is based on chemical tests the significance of which is far from evident. Justi-
fication for the line EF is claimed on the ground that evolutions of heat have been
reported by Carpenter and Keeling as occurring at 1050 to 1100 deg. Other ob-
servers, however, have generally failed to detect these retardations. There are
2700
2500 -
2300'
8100
1900
1700
700
S 1 2 3 4 5 6 7 3
Fig. 433. Ruff's equilibrium diagram.
10
other serious objections to Upton's diagram and its construction is so highly specula-
tive as to render its closer study inadvisable in these pages.
Ruff's Diagram. Professor Ruff has published the equilibrium diagram repro-
duced in Figure 433, which, it will be noted, is of the double type, GK representing
equilibrium with graphite and SK with cementite. The diagram does not extend
below the eutectoid line PK but includes alloys containing as much as 10 per cent
carbon. The line D'H indicates the increasing solubility of carbon in iron with in-
creasing temperature. At some 2200 deg. C. molten iron saturated with carbon
contains nearly 10 per cent of that element. At this temperature Ruff believes that
the alloy consists of the carbide Fe 2 C as explained in Chapter XXII. As the tem-
perature increases above 2200 deg. the solving power of iron for carbon decreases as
450 CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IRON-CARBON ALLOYS
indicated by the line HI, carbon being rejected, probably through the breaking up
of some Fe 2 C into iron and graphite (see Chapter XXII). At some 2700 deg. iron
can retain but a little over 7 per cent of carbon in solution. In cooling below 2200
deg. (line HD') graphite and Fe 3 C are formed from the transformation of Fe 2 C
(3Fe 2 C = 2 Fe 3 C + C).
1 234 SO 1 8 9 10
Fig. 434. Wittorff's equilibrium diagram.
Wittorff 's Diagram. N. M. Wittorff worked out the diagram reproduced in
Figure 434. It will be noted that (1) starting with an alloy containing some 11 per
cent carbon, as it cools from T to R, that is, from some 2400 to 2000 deg. C. the
carbide FeC 2 crystallizes out according to the diagram, (2) between R and M (2000
to 1700 deg.) Fe 3 C forms through the transformation of some FeC 2 (3) between M
and D (1700 to 1350 deg.) both FeC and Fe 4 C are formed necessarily at the expense
of FeC 2 which disappears and possibly also through the transformation of some of
the Fe 3 C, and (4) below D (1350 deg.) the liquid phase disappears.
CHAPTER XXVI EQUILIBRIUM DIAGRAM OF IRON-CARBON ALLOYS 451
Investigations of a region of the equilibrium diagram but little explored should
be welcomed but in view of the fact that the experimental results of the different
observers as well as the conclusions based upon them are at such variance, it seems
advisable to omit from these pages a closer scrutiny of these recent diagrams. When
some of the points that need clearing up have been settled the matter involved will
be duly incorporated in a subsequent edition of this treatise.
CHAPTER XXVII
THE PHASE RULE
The Phase Rule to which references have been made in the preceding chapters
should now be considered as it has been found of much assistance in interpreting cor-
rectly the iron-carbon equilibrium diagram.
Enunciation of the Phase Rule. The phase rule was enunciated in 1878 by Wil-
lard Gibbs, at the time Professor of Physics in Yale University. It is one of the most
notable contributions ever made to physical chemistry.
The phase rule deals with the equilibrium of systems and is generally expressed
by the formula:
F = C + 2-P
showing the relation existing between the degrees of freedom (F) of a system, the num-
ber of components (C), and the number of phases (P); it tells us that the number of
degrees of freedom of any system is equal to the number of its components plus two,
minus the number of phases present. In order to understand the phase rule and its
application, it is necessary and sufficient to have an accurate understanding of the
meaning of the terms employed in its enunciation, namely, equilibrium, degrees of
freedom, components, and phases.
Equilibrium. A substance or system may be said to be in a state of equilibrium
when it is chemically and physically at rest, meaning by chemical rest that chemical
compounds are neither being dissociated nor formed, and by physical rest, not the
absence of motion but the absence of molecular transformation, such as changes of
state or allotropic changes. It is necessary, however, to distinguish between homo-
geneous and heterogeneous substances. A substance is said to be homogeneous when it
is chemically and physically uniform throughout, i.e. when any two portions of it pos-
sess identical chemical and physical properties. Homogeneous substances are neces-
sarily gaseous mixtures, elements, chemical compounds, or liquid and solid solutions.
The equilibrium of a homogeneous system is sometimes called homogeneous equi-
librium. A heterogeneous substance is made up of two or more physically separate
parts, that is, of parts having different physical properties. Ice and water, many
rocks, and many alloys are instances of heterogeneous substances. If the com-
ponent parts of heterogeneous substances may be present in indefinite proportions,
the substances are mechanical mixtures; if they occur in definite proportions, the
substances are eutectic or eutectoid alloys. The equilibrium of heterogeneous systems
is sometimes called heterogeneous equilibrium.
Howe has recently suggested that the homogeneous constituents of alloys be called
"metarals" because of the great analogy between the constitution of metallic alloys
and of rocks, the minerals being the homogeneous components of the latter, while the
word aggregate is very frequently used to designate heterogeneous alloys. In metal-
452
CHAPTER XXVII THE PHASE RULE 453
lography, therefore, metarals and aggregates may conveniently replace the equivalent
terms, homogeneous and heterogeneous substances, of the physical chemist.
Only three independently variable factors can affect the equilibrium of a system,
namely, (1) the temperature, (2) the pressure, and (3) the concentration or composi-
tion. If arbitrary values may be given to one or more of these factors without destroy-
ing the chemical and physical rest of the system, its equilibrium is said to be stable.
On the contrary, if a change in value of any one of these three factors results in chemi-
cal or physical transformation, i.e. in atomic or molecular activity such as dissociation
or formation of chemical compounds, changes of state, or allotropic changes, the
equilibrium of the system was unstable. Water under atmospheric pressure is in
stable equilibrium, for we may change its temperature within wide limits without
causing it to undergo a change of state, while of course its chemical composition
remains likewise unaffected. All elements are generally in a state of stable equilib-
rium, as well as an infinite number of substances composed of two or more elements,
for they may be heated, for instance, through wide ranges of temperatures without
upsetting their physico-chemical equilibrium. Examples of unstable equilibrium,
however, are far from uncommon. During the solidification of substances, for in-
stance, stages must generally be passed through during which the equilibrium of the
substance is unstable, and it is often possible through very rapid cooling to retain
in the cold the unstable conditions, because of the rigidity of the substance now
opposing the changes needed for a return to stable equilibrium. It has been seen
in these chapters that hardened steel is, for the above reason, unstable, hence the
possibility of tempering it by slight reheating.
The kind of equilibrium known as metastable remains to be described. Liquids
may be cooled, when taking the necessary precautions, below their normal freezing-
point, without freezing, the phenomenon being known as superfusion, surfusion, or
undercooling, and the substance being said to be in metastable equilibrium.
Water, for instance, may be cooled below deg. C. and still remain liquid.
The introduction of a solid fragment of the substance, a piece of ice in the case
of water, results in the solidification of the liquid while its temperature rises to its
normal freezing-point. Otherwise, the substance may be kept liquid below its
solidification point for any length of time. If the temperature of the liquid con-
tinues to fall, however, a point is reached when its equilibrium becomes unstable, i.e.
when further lowering of temperature causes the liquid to solidify. To state the case
broadly, the failure on the part of a system to undergo a certain chemical or physical
transformation when that transformation is due, although given the necessary time,
results in metastable equilibrium, while its failure to undergo a transformation because
of the necessary time being denied, as in quenching, results in unstable equilibrium.
Metastable equilibrium is stable, at least within narrow limits of temperature, while,
theoretically at least, slight heating of a substance in unstable equilibrium should
result in a partial return to a more stable condition, that is, in a partial occurrence of
the transformation that was suppressed by quick cooling.
Degrees of Freedom. By the degrees of freedom (sometimes called degrees of
liberty), of a system is meant the number of the three independently variable factors,
temperature, pressure, and concentration, which may arbitrarily be made to vary
without disturbing the system's physico-chemical rest. It has already been noted that
a system, in order to be in stable equilibrium, must have at least one degree of free-
dom. It will also be understood that no system can have more than two degrees of
freedom because in the case of arbitrary values being given to two of the factors, the
454 CHAPTER XXVII THE I'll ASK Kl'LK
value of the third is necessarily fixed, this being due to the known rigid relations
existing between temperature, pressure, and concentration.
Systems which have no degree of freedom are said to be "unvariant" or "non-
variant." Their equilibrium is necessarily unstable. Systems having one degree of
freedom are called "univariant" or "monovariant," and those with two degrees of
freedom "bivariant" or "divariant."
Phases. By the phases of a system are meant the homogeneous, physically dis-
tinguishable, and mechanically separable constituents of that system. Water and ice,
for instance, are possible phases of the water-ice system; quartz, felspar, and mica are
phases of granite, that is, of the silica-alumina-potash system. It will be apparent that
phases must necessarily be gaseous mixtures, elements, definite chemical compounds,
or solutions. As previously mentioned, Howe, following the petrographical nomencla-
ture, and noting that the minerals are the phases of rocks, calls "metarals" the phases
of metals and alloys.
Components. The components of a system are described by Findlay as "those
constituents the concentration of which can undergo independent variation in the
different phases," by Bancroft as "substances of independently variable concentra-
tion," by Mellor as those "entities which are undecomposable under the conditions
of experiments," by Howe as "free elements and those compounds which in the nature
of the case are undecomposable under the conditions contemplated, and so play the
part of elements." The components of a system may be either chemical compounds
or elements, but there is at times some difficulty in grasping the distinction between
the components of a system and its ultimate chemical constituents. The criterion by
which to decide whether an entity is or is not a component, is the possibility of in-
dependent variation in the different phases. Take the system water, for instance:
evidently water and not hydrogen and oxygen is the component, because any
variation in the proportion of hydrogen would necessarily imply a corresponding
and well-defined variation in the proportion of oxygen and vice versa. Findlay
writes :
"In deciding the number of components in any given system, not only must the
constituents chosen be capable of independent variation, but a further restriction is
imposed, and we obtain the following rule: As the components of a system there are to be
chosen the smallest number of independently variable constituents by means of which
the composition of each phase participating in the state of equilibrium can be expressed
in the form of a chemical equation."
In the case of alloys, however, such difficulty does not arise, for the constituent
metals are always the components of the systems.
The Phase Rule Applied to Alloys. In dealing with alloys we may for all practi-
cal purposes ignore the influence of pressure, seeing that because of their feeble vola-
tility they are practically always subjected to atmospheric pressure. Omitting the
influence of pressure necessarily reduces by one the possible number of degrees of
freedom so that in the case of alloys the phase rule may be expressed by the formula :
F = C + 1 - P
signifying that the number of degrees of freedom is equal to the number of components
plus one, minus the number of phases. Since to be in stable equilibrium a system must
have at least one degree of freedom, it is obvious that an alloy made up of n metals
cannot have more than n phases. If it had n + 1 phases it would have no degree of
freedom, that is, its equilibrium would be unstable. With n - 1 phases it would have
CHAPTER XXVII THE PHASE RTLE
455
two degrees of freedom. It could not have less than n 1 phases, since it cannot have
more than two degrees of freedom.
The Phase Rule Applied to Pure Metals. Pure metals have only one component,
hut their possible phases are (1) liquid metal, (2) solid metal, (3) several allotropic con-
ditions of the solid metal. Let us consider Figure 435, which represents the solidi-
fication of a pure metal as explained in Chapter XXV.
Above the temperature T the metal is entirely liquid; it has but one phase, and
consequently one degree of freedom (F =1 + 1 1 = 1). The system above T is
univariant; its temperature may be altered within wide limits-^vjthout disturbing its
I
^ T
/ /me
Fig. 4:i r >. Equilibrium of pun; metals according to the Phase Rule.
equilibrium: it remains liquid. At the temperature T two phases are present, solid
metal and liquid metal, the metal having, therefore, no degree of freedom (F = 1 + 1
2 = 0): it is non-variant. Liquid and solid metal can exist only at one temperature,
the critical temperature of solidification, any change of its temperature resulting in
the disappearance of one of the phases, that is, in a return to stable equilibrium.
Increasing the temperature must result in the disappearance of the solid phase, while
lowering the temperature must cause the disappearance of the liquid phase. Below
the temperature T the system contains only the solid phase, being, therefore, univari-
ant: its temperature may be varied arbitrarily.
The Phase Rule Applied to Binary Alloys. Binary alloys having for components
the two alloying metals, the formula of the phase rule becomes:
F = 2+ 1 - P
or F = 3 - P
456
CHAPTER XXVII THE PHASE RULE
Clearly binary alloys when in a condition of stable equilibrium cannot have more than
two phases. With one phase they will be bivariant, with two phases univariant, and
with three phases non-variant. Let us apply the rule to the fusibility curves of binary
alloys of metals partially soluble in each other when solid (Fig. 436). Above the liqui-
dus MEM' there is but one phase present, namely the liquid phase, the system being,
therefore, bivariant (F = 3 - 1 = 2), i.e. both temperature and concentration may be
varied arbitrarily without upsetting the equilibrium of the system, which means, in
the case under consideration, without causing its solidification. On reaching any
point L of the liquidus the alloy begins to solidify, and two phases are now present,
namely, solid solution and liquid alloy, the system becomes univariant (F = 3 - 2 = 1).
Having but one degree of freedom only the temperature or the concentration may be
Fig. 436. Equilibrium according to the Phase Rule of binary alloys whose component mchils .-ire
partially soluble in each other in the solid state.
arbitrarily varied. Should we, for instance, lower the temperature of alloy R from T
to T' (Fig. 436) the composition of the liquid phase necessarily shifts from L to L', and
that of the solid phase in equilibrium with it from s to s'. In the region MSES'M' of
the diagram bounded by the liquidus and solidus lines, therefore, the alloys are uni-
variant, any arbitrary change of temperature resulting in a well-defined change of
concentration and vice versa. At E, corresponding to eutectic composition and
eutectic temperature, three phases are present, namely two solid solutions and liquid
alloy, the system having no degree of freedom (F = 3 3 = 0) . Neither the tempera-
ture nor the concentration may be altered without causing the disappearance of at
least one of the phases. Increasing the temperature must result in the disappear-
ance of both solid solutions, the system becoming bivariant, while lowering it must
be followed by the disappearance of the liquid phase. Again, shifting the concen-
tration to the left or right of E must yield the univariant system solid solution plus
liquid. Clearly two solid phases and a liquid phase can only exist at one critical
temperature and for one critical composition of the alloy; in the case of a eutectic
CHAPTER XXVII THE PHASE RULE 457
alloy these three phases can exist only at its freezing temperature. In the areas
AMSB and DM'S'C single homogeneous solid solutions only are present, that is, but
one phase exists, and the corresponding alloys have, therefore, two degrees of freedom.
Arbitrary changes both of temperature and composition within these areas do not
disturb the equilibrium of the system. Within the region BSS'C two phases occur,
solid solution M and solid solution M', the corresponding alloys having, therefore, but
one degree of freedom. Increasing the temperature from P to P', for instance, must
result in shifting the composition of the solid solutions respectively from R to R' and
from to 0'.
The Phase Rule Applied to Iron-Carbon Alloys. Since iron-carbon alloys belong
to the class of binary alloys the constituents of which are partially soluble in each
other in the cold, the application of the phase rule to their equilibrium diagram should
not present any difficulty, but we have now to consider allotropic changes as well as
changes of state. Their possible phases or metarals are: (1) liquid iron, (2) liquid
solution of carbon (or FesC) in iron, (3) solid solution (austenite) of carbon (or FesC)
in gamma iron, (4) solid gamma iron, (5) solid beta iron, (6) solid alpha iron (ferrite),
(7) solid solution (martensite) 1 of carbon (or FesC) in beta iron, (8) solid cementite,
(9) graphite, and possibly others. The exact nature of troostite and sorbite being
still in doubt, they are not here classified as phases, seeing that they may be, and
probably are, aggregates of two or more phases, unless indeed they be, according to
Benedicks, emulsions or colloidal solutions. Scientists do not agree, however, as to
whether colloidal solutions are or are not phases, opinions differing in regard to their
homogeneity. Indeed some writers like Le Chatelier question the existence of colloidal
solutions which they consider as finely divided aggregates. Pearlite evidently is not
a phase, but an aggregate of the two phases, ferrite and cementite, in constant pro-
portion after the fashion of eutectic and eutectoid mixtures.
Let us now apply the teachings of the phase rule to the iron-carbon equilibrium
diagram (Fig. 437) . The number and kinds of phases existing at different temperatures,
and for different proportions of the components, iron and carbon, have been clearly
indicated and will be readily understood in view of the foregoing considerations.
Above the liquidus LEU all alloys^ are composed of but one liquid phase, and have,
therefore, two degrees of freedom; between the liquidus and solidus, that is, in the region
LSE and L'S'E, two phases are present, liquid solution plus solid solution (austenite),
or liquid solution plus solid FesC, hence the corresponding alloys have here but one
degree of freedom^ (alloys of composition E and at the corresponding temperature are
evidently made up of three phases, namely liquid solution plus solid austenite plus
solid cementite, being, therefore, non-variant; in the region LADS all alloys being com-
posed of but one phase, namely, solid austenite, are bivariant; at D the alloy contains
three phases, ferrite, cementite, and austenite, and is, therefore, non- variant; in the
area DSS'F two phases are present, solid solution (austenite) plus cementite, and the
system has but one degree of freedom. If, as is often the case, cementite is in this
region decomposed into iron and graphite the alloys are for the time being non-variant,
becoming again univariant on the complete disappearance of cementite. In the region
ABH beta iron and austenite are present, the alloys having in consequence but one
degree of freedom; in the region BCDH alpha ferrite and austenite are present and
the alloys, therefore, are univariant. Finally below CDF three possible cases should
be considered: (I) the cementite formed during solidification and subsequent cooling
1 All investigators do not, agree as to the homogeneity, that is the phase-like character of marten-
site, some still regarding it as an aggregate.
458
CHAPTER XXVII THE Pi [ASK RULE
<0
CHAPTER XXVII THE PHASE RULE 459
remains unchanged, in which case the alloys are made up of the two phases ferrite and
cementite, being, therefore, univariant, their equilibrium, however, as previously ex-
plained, is supposed to be metastable; (II) the cementite has been completely con-
verted into ferrite and graphite, only those two phases being present, undoubtedly
representing the stable equilibrium of all iron-carbon alloys; (III) the dissociation of
cementite has been incomplete, both cementite and graphite being present, which
with ferrite give three phases, the corresponding alloys being non-variant and, there-
fore, their equilibrium unstable. Condition (I) generally prevails in all grades of steel,
and is readily produced in cast iron by rapid cooling especially Jnjthe absence of con-
siderable silicon, the resulting alloys being known as white cast iron. Condition (II)
never obtains in steel, but may be produced in highly carburized alloys by very slow
cooling through and below solidification, especially in the presence of much silicon
and in the absence of manganese and sulphur. Condition (III) is the condition of the
gray cast irons of commerce, their compositions and other influences prevailing during
their cooling being such as to cause the graphitizing of varying proportions of cementite.
APPENDIX
REPORT OF COMMITTEE 53 OF THE INTERNATIONAL ASSOCIATION FOR
TESTING MATERIALS
ON THE NOMENCLATURE OF THE MICROSCOPIC SUBSTANCES
AND STRUCTURES OF STEEL AND CAST IRON
Presented by the Chairman H. M. HOWE and the Secretary of the Committee ALBERT SAUVEUR
at the VI th Congress, New York, September, 1912
The Committee for studying this problem is constituted as follows:
Professor H. M. HOWE, Chairman, New York.
Professor ALBERT SAUVEUR, Secretary, Cambridge, Mass.
Members: F. OSMOND, Paris; Dr. H. C. H. CARPENTER, Manchester; Prof. W.
CAMPBELL, New York; Prof. C. BENEDTCKS, Stockholm; Prof. F. WUST, Aachen;
Prof. A. STANSFIELD, Montreal; Dr. J. E. STEAD, Middlesbrough; Prof. L. GUILLET,
Paris; Prof. E. HEYN, Berlin-Lichterfelde; Dr. W. ROSENHAIN, Teddington.
I. GENERAL PLAN
We first enumerate the substances of such importance as to warrant it, indicating
roughly their constitution, and then define and describe certain of them.
The conditions which we meet are (1) that we need definitions on which all can
agree; and this implies that they must be free from all contentious matter and be
based on what all admit to be true; (2) that the reader must needs know the current
theories as to the constitution of these substances, and these theories are necessarily
contentious. We meet these conditions by the plan of giving (1) the Name which we
recommend for general use, followed immediately in parentheses by the other names
used widely enough to justify recording them; (2) the Definition proper, based on an
undisputed quality, e.g. that of austenite, which we base on its being an iron-carbon
solid solution, purposely omitting all reference to the precise nature of solvent and
solute; and (3) Constitution, etc., etc., in which we give the current theories as to the
nature of solvent and solute and appropriate descriptive matter.
The distinction between these three parts should be understood. (1) The Names
actually used are matters of record and indisputable. (2) The Definitions are matters
of convention or treaty, binding on the contracting parties, though subject to de-
nouncement, preferably based on some determinable property of the thing defined as
distinguished from any theory as to its nature, or if necessarily based on any theory
it should be a theory which is universally accepted. It is a matter purely of conven-
tion and general convenience what individual property of the thing defined shall
form the basis of the definition. The name and the definition should endure perma-
nently, except in the case of a definition based on an accepted theory, which must be
460
APPENDIX NOMENCLATURE OF THE MICROSCOPIC CONSTITUENTS 461
changed if the theory should later be disproved. (3) Theories and Descriptions are
not matters of agreement or convention but dependent on observation, and therefore
always subject to be changed by new discoveries. They are temporary in their nature
as distinguished from the names and definitions which should be fixed, at least rela-
tively.
This case of austenite illustrates the advantage of non-indicative names. The
names which we propose to displace, "gamma iron" and "mixed crystals," imply
definite theories as to the nature of austenite, and hence might have to be abandoned
in case those theories were later disproved. The name "austenite" implies nothing,
like mineralogical names in general, and hence is stable in itself. Our infant branch
of science may well learn from its elder sister, which has tried and proved the advan-
tage of this non-indicative naming.
In those cases in which a name has been used in more than one sense we advise
the retention of one and the abandonment of the others, having obtained the consent
of the proposers of such names for their abandonment.
Many whose judgment we respect object to our including certain of the less used
names, e.g. from i to n in our list, holding them either to be confusing or to be needless.
It is true that several names (hardenite, martensite, sorbite, etc.), have been used
with various meanings, and hence confusingly, in spite of which most of them should
be retained, each with a single sharp-cut definition, because they are so useful.
As regards the alleged needlessness of certain names it is for each writer to decide
whether he does or does not need names with nice shades of meaning, such as osmon-
dite and troosto-sorbite. Those who look only at the general outlines and not at the
details have no right to forbid the workers in detail from having and using words
fitting their work; nor have those whose needs are satisfied by the three primary
colors a right to forbid painters, dyers, weavers, and others from naming the many
shades with which they are concerned. Like the lexicographer we must serve the
reader by explaining those words which he will meet, whether we individually use or
condemn them. We feel that we have exhausted our powers in cautioning writers
that certain words are rare and not likely to be understood by most readers, or are
improper for any reason, and in urging the complete abandonment of those with-
drawn by their proposers.
Needless words will die a natural death; needed ones we cannot kill. The good
we might do in hastening the death of the moribund by omitting them from this re-
port is less than the good we do by teaching their meaning to those who will meet
them in ante-mortem print. These readers have rights. We serve no class, but the
whole.
Illustrations. At the end of the several descriptions the reader is referred to
good illustrations in Osmond and Stead's "Microscopic Analysis of Metals," Griffin
& Co., London, 1904.
II. LIST OF MICROSCOPIC SUBSTANCES
The microscopic substances here described consist of
1. Meiarals, true phases, like the minerals of nature. These are either elements,
definite chemical compounds, or solid solutions and hence consisting of definite sub-
stances in varying proportions. These include austenite, ferrite, cementite, and
graphite.
462 APPENDIX NOMENCLATURE OF THK MICROSCOPIC CONSTITUENTS
2. Aggregates, like the petrographic entities as distinguished from the true minerals.
These mixtures may he in definite proportions, i.e. eutectic, -or eutectoid mixtures
(ledeburite, pearlite, steadite), or in indefinite proportions (troostite, sorbite). Those
aggregates which are important for any reason are here described.
(Many true minerals, such as mica, felspar, and hornblende, are divisible into
several different species so that these true mineral names may be either generic or
specific. These genera and species are definite chemical compounds in which one
element may replace another. Other minerals, such as obsidian, are solid solutions
in varying proportions, and in these also one element may replace another. Metarals
like minerals differ from aggregates in being severally chemically homogeneous.)
These two classes may be cross classified into :
(A) The iron-carbon series, which come into being in cooling and heating.
(B) The important impurities, manganese sulphide, ferrous sulphide, slag, etc.
(C) Other substances.
The most prominent members of the iron-carbon series are:
I. molten iron, metaral, molten solution, but hardly a microscopic constituent;
II. the components which form in its solidification :
(a) austenite, solid solution of carbon or iron carbide in iron, metaral,
(6) cementite, definite metaral, Fe 3 C,
(c) graphite, definite metaral, C;
III. the transition substances which form through the transformation of austenite
during cooling:
(d) martensite, metaral of variable constitution; its nature is in dispute;
(e) troostite, indefinite aggregate, uncoagulated mixture,
(/) sorbite, indefinite aggregate, chiefly uncoagulated pearlite plus ferrite or ce-
mentite;
IV. products 1 of the transformation of austenite:
(g) ferrite,
(/*) pearlite.
This transformation may also yield cementite and graphite as end products in
addition to those under 6 and c.
In addition to the above, the names of which are universally recognized and in
general use, the following names have been used more or less:
(i) ledeburite (Wiist), definite aggregate, the austenite-cementite eutectic;
(j) ferronite (Benedicks), hypothetical definite metaral, ft iron containing about
0.27 per cent of carbon;
(k) steadite (Sauveur) , definite aggregate, the iron-phosphorus eutectic (rare) ;
and three transition stages in the transformation of austenite, viz. :
(I) hardenite (Arnold), collective name for the austenite and martensite of eutec-
toid composition;
(m) osmondite (Heyn), boundary stage between troostite and sorbite;
(ri) troosto-sorbite (Kourbatoff ) , indefinite aggregate, the troostite and the sorbite
which lie near the boundary which separates these two aggregates (obsolescent) .
'In hypo-eutectoid steels these habitually play the part of end products, though according to
the belief of most the true end of the transformation is not reached till the whole has changed into
a conglomerate of ferrite plus graphite.
APPENDIX NOMENCLATURE OF THE MICROSCOPIC CONSTITUENTS 463
III. DEFINITIONS AND DESCRIPTIONS
Carbon-Iron Equilibrium Diagram, Figure 438. Under the several substances
about to be described an indication will be given of the parts of the carbon-iron equi-
librium diagram Figure 438 to which they severally correspond.
Austenite, Osmond (Fr. Austenite, Ger. Austenit, called also mixed crystals and
gamma iron. Up to the year 1900 often called martensite and wrongly sometimes
still so called). Metaral of variable composition.
Definition. The iron-carbon solid solution as it exists above the transformation
1500
1400
1300
1200
A
iooo-
rj
I*
o
B 900-
o
H
800-
M
700-
600-
500-
1.
Molten Iron
(Per Fondu)
Molten
(Per Fondu)
f
flusbenibe
C
/
3.
/Austenite
5.
Austenite + Cementite
Pearl ite
8.B.
Cementite
Pearl ite
K
1 2 3 4 5
Carbon per cent
Y\K. 438. A,: The line PSK is often called "Ai". A 3 : The line COS is often called "A,", and
this name is sometimes applied to the line SE.
range or as preserved with but moderate transformation at lower temperatures, e.g.
by rapid cooling, or by the presence of retarding elements (Mn, Ni, etc.), as in 12 per
cent manganese steel and 25 per cent nickel steel.
Constitution and Composition. A solid solution of carbon or iron carbide (prob-
ably Fe 3 C) and gamma iron, normally stable only above the line PSK of the carbon-
iron diagram. It may have any carbon content up to saturation as shown by the line
SE, viz.: about 0.90 per cent at S (about 725 deg. C.) to 1.7 per cent at E (about
1130 deg.). The theory that the iron and the carbide or carbon, instead of being dis-
solved in each other, are dissolved in a third substance, the solution of eutectoid com-
464 APPENDIX NOMENCLATURE OF THE MICROSCOPIC CONSTITUENTS
position (Fe 24 C, called hardenite) is not in accord with the generally accepted theory
of the constitution of solutions, and is not entertained widely or by any member of
this committee.
Crystallization. Isometric. The idiomorphic vug crystals are octahedra much
elongated by parallel growth. The etched sections show much twinning. (Osmond
and most authorities.) Le Chatelier believes it to be rhombohedral. Cleavage
octahedral.
Varieties and Genesis. (l) Primary austenite formed in the solidification of carbon
steel and hypo-eutectic cast iron; (2) eutectic austenite, interstratified with eutectic
cementite, making up the eutectic formed at the end of the solidification of steel con-
taining more than about 1.7 per cent of carbon, and of all cast iron.
Equilibrium. It is normal and in equilibrium in Region 4, and also associated
with beta iron in Region 6, with a iron in Region 7, and with cementite in Region 5.
It should normally transform into pearlite with either ferrite or cementite on cooling
past AI into Region 8.
Transformation. In cooling slowly through the transformation range, Ar 3 - Ari,
austenite shifts its carbon content spontaneously through generating pro-eutectoid
ferrite or cementite, to the eutectoid ratio, about 0.90 per cent, and then transforms
with increase of volume at Ari into pearlite, q.v., with which the ejected ferrite or
cementite remains mixed. Rapid cooling and the presence of carbon, manganese, and
nickel obstruct this transformation, (1) retarding it, and (2) lowering the temperature at
which it actually occurs, and in addition (3) manganese and nickel lower the temperature
at which in equilibrium it is due. Hence, by combining these four obstructing agents
in proper proportions the transformation may be arrested at any of the intermediate
stages, martensite, troostite, or sorbite, 1 q.v., and if arrested in an earlier stage it
can be brought to any later desired stage by a regulated reheating or "tempering."
For instance, though a very rapid cooling in the absence of the three obstructing ele-
ments checks the transformation but little and only temporarily, yet if aided by the
presence of a little carbon it arrests the transformation wholly in the martensite
stage; and in the presence of about 1.50 per cent of carbon such cooling retains about
half the austenite so little altered that it is "considerably" softer than the usually
darker needles of the surrounding martensite, with which it contrasts sharply. Again,
either (a) about 12 per cent of manganese plus 1 per cent of carbon, or (6) 25 per cent
of nickel, lower and obstruct the transformation to such a degree that austenite per-
sists in the cold apparently unaltered, even through a slow cooling. (Hadfield's man-
ganese steel and 25 per cent nickel steel, manganiferous and nickeliferous austenite
respectively.)
Occurrence. When alone (12 per cent manganese and 25 per cent nickel steel
and Maurer's 2 per cent carbon plus 2 per cent manganese austenite) polyhedra, often
coarse, much twinned at least in the presence of martensite, and readily developing
slip bands. In hardened high-carbon steel it forms a ground mass pierced by zigzag
needles and lances of martensite.
Etching. All the common reagents darken it much more than cementite, less
1 Though the transformation can be arrested in such a way as to leave the whole of the steel
in the condition of martensite, it is doubted by some whether it can be so arrested as to leave the
whole of it in any of the other transition stages. Troostite and sorbite caused by such arrest are
habitually mixed, troostite with martensite or sorbite or both, and sorbite with pearlite or troostite
or both.
APPENDIX NOMENCLATURE OF T1IK MICROSCOPIC CONSTITUENTS 465
than troostite or sorbite, and usually less, though sometimes more, than martensite,
which is recognized by its zigzag shape and needle structure. With ferrite and pearlite
it is never associated.
Physical Properties. Maurer's austenite of 2 per cent manganese plus 2 per
cent carbon is but little harder than soft iron, and 25 per cent nickel steel and Had-
field's manganese steel are but moderately hard. Yet as usually preserved in hardened
high carbon steel, the hardness of austenite does not fall very far short of that of the
accompanying martensite, probably because partly transformed in cooling-. (Os-
mond's words are that it is "considerably" softer than that martensite.)
Specific Magnetism. Very slight unless perhaps in intenselieTds. In Hadfield's
manganese steel and 25 per cent nickel steel, very ductile.
Illustrations. "Microscopic Analysis of Metals," Figures 20, 50, and 51 on
pp. 39, 100, and 101.
Cementite (Sorby, "intensely hard compound"; Ger. Cementit, Fr. Cementite;
Arnold, crystallized normal carbide). Definite metaral.
Definition. Tri-ferrous carbide, Fe 3 C. The name is extended by some writers
so as to include tri-earbides in which part of the iron is replaced by manganese or
other elements. Such carbides may be called " manganiferous Cementite," etc.
Occurrence. (a) Pearlitic as a component of pearlite, q.v.; (6) eutectic;
(c) primary or pro-eutectic; (d) pro-eutectoid; (e) that liberated by the splitting up of
the eutectic or of pearlite; and (/) uncoagulated in sorbite, troostite, and perhaps mar-
tensite. (c), (d), and (e) are grouped together as "free" or "massive."
Primary cementite is generated in cooling through Region 3; eutectic cementite
on cooling past the line EBD; pro-eutectoid cementite in cooling through Region 5;
pearlitic cementite on cooling past the line PSK, or AI. Though the several varieties
of cementite are generally held to be all metastable, tending to break up into graphite
plus either austenite above AI or ferrite below A], yet they have a considerable and
often great degree of persistence. The graphitizing tendency is completely checked
in the cold but increases with the temperature and with the proportion of carbon
and of silicon present, and is opposed by the presence of manganese.
Crystallization. Orthorhombic, in plates.
Structure. (a) Pearlitic, in parallel unintersecting plates alternating with plates
of ferrite; (6) eutectic, plates forming a network filled with a fine conglomerate
of pearlite with or without pro-eutectoid cementite; (c) primary, in manganiferous
white cast iron, etc., in rhombohedral plates; (d) in hyper-eutectoid steel, pro-eutec-
toid cementite forms primarily a network enclosing meshes of pearlite through which
cementite plates or spines sometimes shoot if the network is coarse; (e) cementite
liberated from pearlite merges with any neighboring cementite; (/) the structure of
uncoagulated cementite cannot be made out. On long heating the pro-eutectoid
and pearlitic cementite spheroidize slowly, and neighboring particles merge; (a) in
white irons rich in phosphorus in flat plates embedded in iron-carbon-phosphorus
eutectic.
Etching, etc. After polishing stands in relief. Brilliant white after etching with
dilute hydrochloric or picric acid; darkened by boiling with solution of sodium picrate
in excess of sodium hydrate.
Physical Properties. Hardest component of steel. Hardness = 6 of Mohs scale.
Scratches glass and felspar but not quartz; very brittle. Specific magnetism about
two thirds that of pure iron.
460 APPENDIX NOMENCLATURE OF THE MICROSCOPIC CONSTITUENTS
Illustrations. "Microscopic Analysis of Metals," Figures 42 and 43 on
pp. 84, 85.
Martensite (Fr. Martensite, Ger. Martensit). Metaral. Its nature is in dispute.
Definition. The early stage in the transformation of austenite characterized by
needle structure and great hardness, as in hardened high-carbon steel.
Constitution. I. (Osmond and others.) A solid solution like austenite, q.v., ex-
cept that the iron is partly beta, whence its hardness, and partly alpha, whence its
magnetism in mild fields. II. (Le Chatelier.) The same except that its iron is essen-
tially alpha, and the hardness due to the state of solid solution. III. (Arnold.) A spe-
cial structural condition of his "hardenite" (austenite); not widely held. IV. A solid
solution in gamma iron. V. (Benedicks.) The same as I, except that the iron is wholly
beta and that beta iron consists of alpha iron containing a definite quantity of gamma
iron in solution.
Equilibrium. It is not in equilibrium in any part of the diagram, but represents
a metastable condition in which the metal is caught during rapid cooling, in transit
between the austenite condition stable above the line Ai and the condition of ferrite
plus cementite into which the steel habitually passes on cooling slowly past the
line AI.
Occurrence. The chief constituent of hardened carbon tool steels, and of medium
nickel and manganese steels. In still less fully transformed steels (1.50 per cent
carbon steel rapidly quenched, etc.) it is associated with austenite; in more fully
transformed ones (lower carbon steels hardened, high carbon steels oil hardened, or
water hardened and slightly tempered, or hardened thick pieces even of high carbon
steel) it is associated with troo'stite, and with some pro-eutectoid ferrite or cementite,
q.v., in hypo- and hyper-eutectoid steels respectively. In tempering it first changes
into troostite; at 350 deg. -400 deg. it passes through the stage of osmondite; at
higher temperatures it changes into sorbite; and at 700 deg. into granular pearlite.
On heating into the transformation range this changes into austenite, which on cool-
ing again yields lamellar pearlite.
Characteristic specimens are had by quenching bars 1 cm. square of eutectoid
steel, i.e. steel containing about 0.9 per cent of carbon, in cold water from 800 (leg. C.
(1472 deg. F.).
Structure. When alone, habitually in flat plates made up of intersecting needles
parallel to the sides of a triangle. When mixed with austenite, zigzag needles, lances,
and shafts.
If produced by quenching after heating to 735 deg. C., it consists of minute crystal-
lites resembling the globulites of Vogelsang, which are rarely arranged in triangular
order. At times so fine as to suggest being amorphous.
Etching. With picric acid, iodine or very dilute nitric acid etches usually darker
than austenite, but sometimes lighter, always darker than ferrite and cementite, but
always lighter than troostite.
Illustrations. "Microscopic Analysis of Metals," Figure 19 on p. 38, Figure 52
on p. 102.
Ferrite (Fr. Ferrite, Ger. Ferrit). Definite metaral.
Definition. Free alpha iron.
Composition. Nearly pure iron. It may contain a little phosphorus and
silicon but its carbon content, if any, is always small, at the most not more than 0.05
per cent, and perhaps never as much as 0.02 per cent.
APPKXDIX XOMKXCLA'ITKK OF THE MICROSCOPIC COXSTITUENTS 467
Occurrence. (a) Pearl i tic as a component of pearlite, q.v.; (b) pro-eutectoid
ferrite generated in slow cooling through the transformation range; (c) that segre-
gated from pearlite, i.e. set free by the splitting up of pearlite, especially in low car-
bon steel; (d) uncoagulated as in sorbite, and probably troostite. (b) and (c) are
classed together as free or massive.
Thus ferrite is normal and stable in regions 7 and 8.
Crystallization. Isometric, in cubes or octahedra.
Structure. (a) Pearlitic ferrite, unintersecting parallel plates alternating with
plates of ceincntite; (b) pro-eutectoid ferrite in low carbon steel forms irregular poly-
gons, each with uniform internal orientation. In higher carbon steel after moderately
slow cooling, especially in the presence of manganese, it forms a network enclosing
meshes of pearlite. In slower cooling this network is replaced by irregular grains
separated by pearlite; (c) the ferrite set free by the splitting up of pearlite merges
with the pro-eutectoid ferrite, if any; (d) the structure of the ferrite in sorbite, etc.,
cannot be made out.
Etch ini/. Dilute alcoholic nitric or picric acid on light etching leaves the
ferrite grains white with junctions which look dark. Deeper etching, by Heyn's
reagent or its equivalent, reveals the different orientation of the crystals or grains,
(a) as square figures parallel to the direction of the etched surface, (b) as plates which
dip at varying angles and become dark or bright when the specimen is rotated under
oblique illumination. Still deeper etching reveals the component cubes (etching
figures, Atzfiguren), at least if the surface is nearly parallel to the cube faces..
Physical Properties. Soft; relatively weak (tenacity about 40,000 Ibs., per
sq. in.); very ductile; strongly ferro-magnetic ; coercitive force very small.
drain Xize. For important purposes (1) etch deeply enough, e.g. with copper-
ammonium chloride, to reveal clearly the junctions of the grains; (2) count on a photo-
graph of small magnification the number of grains in a measured field so drawn as to
exclude fragments of grains; after (3) determining the true grain boundaries by ex-
amination under high powers (Heyn's method). Deep nitric acid etching is inaccurate,
because an apparent grain boundary may contain several grains.
Illustrations. " Microscopic Analysis of Metals," Figures 41, 56 on pp. 79, 116.
Osmondite (Fr. Osmondite, Ger. Osmondit).
Definition. That stage in the transformation of austenite at which the solubility
in dilute sulphuric acid reaches its maximum rapidity. Arbitrarily taken as the
boundary between troostite and sorbite.
Earlier Definition. Denned by the V th Congress as having the "maximum sol-
ubility in acids and by a maximum coloration under the action of acid metallographic
reagents." The present definition is confined to maximum rapidity of dissolving,
because we do not yet know that this in all cases co-exists with the maximum depth
of coloration, and in any case in which these two should not co-exist, the old defini-
tion does not decide which is true osmondite.
Constitution. The following hypotheses have been suggested, none of which
has firm experimental foundation: (1) A solid solution of carbon or an iron carbide
in alpha iron. (2) The colloidal system of Benedicks in its purity, troostite being this
system while forming at the expense of martensite, and sorbite, being this system
coagulating and passing into pearlite. (3) The stage of maximum purity of amor-
phous alpha iron on the way to crystallizing into ferrite.
Occurrence. Hardened carbon steel of about 1 per cent of carbon when reheated
468 APPENDIX NOMENCLATURE OF THE MICROSCOPIC CONSTITUENTS
(tempered) to 350-400 deg. C. passes through the stage of troostite to that of
osmondite, and on higher heating to that of sorhite. What variation if any from this
temperature is needed to bring hardened steel of other carbon content to the osmond-
ite stage is not known. In that it represents a true boundary state between troostite
and sorbite it differs in meaning from troosto-sorbite, which embraces both the troost-
ite and the sorbite which lie near this boundary. Indeed osmondite has sometimes
been used in this looser sense. Writers are cautioned that, however useful these terms
may prove for making these nice discriminations, they are not likely to be familiar
to general readers.
Etching. According to Heyn it differs from troostite and sorbite in being that
stage in tempering which colors darkest on etching with alcoholic hydrochloric acid.
The present definition and description of osmondite should displace previous ones,
because they have the express approval of Professor Heyn, the proposer of the name,
and M. Osmond himself.
Ferronite (Fr.Ferronite, Ger. Ferronit) (Benedicks). Hypothetical definite metaral.
Definition. Solid solution of about 0.27 per cent of carbon in beta iron.
Occurrence (hypothetical). In slowly cooled steels and cast iron containing
0.50 per cent of combined carbon or more, that which is generally believed to be fer-
rite, whether pearlitic or free, is supposed by Benedicks to be ferronite.
Hardenite (Fr. Hardenite, Ger. Hardenit).
Definition. Collective name for austenite and martensite of'eutectoid composi-
tion. It includes such steel (1) when above the transformation range, and (2) when
hardened by rapid cooling.
Observations. On the generally accepted theory that austenite is a solid solution
of carbon or an iron carbide in iron, hardenite is the solution of the lowest transforma-
tion temperature, i.e. the eutectoid. The theory that instead it is a definite chemical
compound, Fe2.iC, is considered under Austenite. Its proposer includes under
hardenite both eutectoid (0.90 per. cent carbon) austenite when above the transforma-
tion range and the martensite into which that austenite shifts in rapid cooling (hard-
ening).
Other Meanings. Originally (Howe, 1888) collective name for austenite and
martensite of any composition in carbon steel. Osmond (1897), austenite saturated
with carbon. Both these meanings are withdrawn by their proposers.
Pearlite (Sorby's "pearly constituent." At first written "pearlyte" Fr. Perlite,
Ger. Perlit). Aggregate.
Definition. The iron-carbon eutectoid, consisting of alternate masses of ferrite
and cementite.
Constitution and Composition. A conglomerate of about 6 parts of ferrite to 1 of
cementite. When pure, contains about 0.90 per cent of carbon, 99.10 per cent of
iron.
Occurrence. Results from the completion of the transformation of austenite
brought spontaneously to the eutectoid carbon content, and hence occurs in all
carbon steels and cast iron containing combined carbon and cooled slowly through
the transformation range, or held at temperatures in or but slightly below that range,
long enough to enable the ferrite and cementite to coagulate into a mass microscopic-
ally resoluble. Hence it is the normal constituent in Region 8. Its ferrite is stable
but its cementite is metastable.and tends to transform into ferrite and graphite.
Varieties and Structure. Because pearlite is formed by the coagulation of the
APPENDIX NOMENCLATURE OF THE MICROSCOPIC CONSTITUENTS 469
ferrite and cementite initially formed as the irresoluble emulsion, sorbite, (Arnold's
sorbitic pearlite) there are the indefinitely bounded stages of sorbitic pearlite (Arnold's
normal pearlite), i.e. barely resoluble pearlite, in the border-land between sorbite and
laminated pearlite; granular pearlite, in which the cementite forms fine globules in a
matrix of ferrite; and laminated or lamellar pearlite, consisting of fine, clearly defined,
non-intersecting, parallel lamellae alternately of ferrite and cementite. The name
granular pearlite was first used by Sauveur to represent what is now called sorbite.
This meaning has been withdrawn.
An objection to Arnold's name "normal poarlite" is that ii^ is likely to mislead.
"Normal" here apparently refers to arising under normal conditions of cooling, but
(1) it rather suggests structure normal for pearlite, which surely is the lamination
characteristic of eutectics in general, and (2) the general reader has no clue as to what
conditions of cooling are here called normal. Many readers are not manufacturers,
and even in manufacture itself air cooling is normal for one branch and extremely
slow furnace cooling for another. Arnold calls troostite "troostitic pearlite" and
sorbite "sorbitic pearlite." This is contrary to general usage, which restricts pearlite
to microscopically resoluble masses.
Etching. After etching with dilute alcoholic nitric or picric acid it is darker than
ferrite or cementite but lighter than sorbite and troostite. A magnification of at
least 250 diameters is usually needed ^or resolving it into its lamellae, though the
pearlite of blister steel can often be resolved with a magnification of 25 diameters.
The more rapidly pearlite is formed, the higher the magnification needed for re-
solving it.
Illustrations. Lamellar pearlite. Osmond and Stead, "Microscopic Analysis,"
Figure 11 on p. 19, Granular pearlite, idem, Figure 18 on p. 36; Heyn and Bauer,
"Stahl und Eisen," 1906, Figure 14, opposite p. 785.
Graphite (Ger. Graphit, Fr. Graphite). Definite metaral.
Definition. The free elemental carbon which occurs in iron and steel.
Composition. Probably pure carbon, identical with native graphite.
Genesis. Derived in large part, and according to Gcerens wholly, from the de-
composition of solid cementite. Others hold that its formation as kish may be from
solution in the molten metal, and that part of the formation of temper graphite may
be from elemental carbon dissolved in austenite. It is the stable form of carbon in
all parts of the diagram.
Occurrence. (1) as kish, flakes which rise to the surface of molten cast iron and
usually escape thence;
(2) as thin plates, usually curved, e.g. in gray cast iron, representing carbon which
has separated during great mobility, i.e. near the melting range;
(3) as temper graphite (Ger. Temperkohle, Ledebur) pulverulent carbon which
separates from cementite and austenite, especially in the annealing process for mak-
ing malleablized castings.
Graphite and ferrite are sometimes associated in a way which suggests strongly
that they represent a graphite-austenite eutectic. But the existence of such a true
eutectic is doubted by most writers.
Properties. Hexagonal. H. 1-2. Gr. 2.255. Streak black and shining, luster
metallic; macroscopic color, iron black to dark steel gray, but always black when seen
in polished sections of iron or steel under the microscope; opaque; sectile; soils paper;
flexible; feel, greasy.
470 APPENDIX NOMENCLATURE OF Till: MICROSCOPIC COXSTlTTKVrs
Troostite (Fr. Troostitc, Ger. Troostit). Probably agrregate. (Arnold, troostitic
pearlite.)
Definition. In the transformation of austenite, the stage following martensite
and preceding sorbite (and osnionditc if this stage is recognized).
< 'oH.fliltilion an/I Composition. An uncoagulated conglomerate of the transition
stages. The degree of completeness of the transformation represented by it is not
definitely known and probably varies widely. Osmond and most others believe that
the transformation, while generally far advanced, yet falls materially short of comple-
tion; but Benedicks and Arnold (9) believe that it is complete. The former belief
that it is a definite phase, e.g. a solid solution of carbon or an iron carbide in either /3
or 7 iron, is- abandoned. Its carbon content like that of austenite and martensite
varies widely.
Occurrence. It arises either on reheating hardened (e.g. martensitie steel) to
slightly below 400 deg., or on cooling through the transformation range at an inter-
mediate rate, e.g. in small pieces of steel when quenched in oil, or quenched in water
from the middle of the transformation range, or in the middle of larger pieces quenched
in water from above the transformation range. With slightly farther reheating it
changes into sorbite; with higher heating into sorbitic pearlite, then slowly into granular
pearlite, and probably indirectly into lamellar pearlite. It occurs in irregular, fine-
granular or almost amorphous areas, colored darker by the common etching reagents
than the martensite or sorbite accompanying it. A further common means of dis-
tinguishing it from sorbite is that it is habitually associated with martensite, whereas
sorbite is habitually associated with pearlite.
Areas near the boundary between troostite and sorbite are sometimes called
troosto-sorbite.
Properties. Hardness, intermediate between that of the martensitic and the
pearlitic state corresponding to the carbon content of the specimen. In general the
hardness increases, the elastic limit rises, and the ductility decreases, as the carbon
content increases. Its ductility is increased rapidly and its hardness and elastic limit
lowered rapidly by further tempering, which affects it much more markedly than
sorbite.
Sorbite (Fr. Sorbite, Ger. Sorbit). Aggregate. (Arnold, sorbitic pearlite.)
Definition. In the transformation of austenite, the stage following troostite
and osmondite if the stage is recognized, and preceding pearlite.
Constitution and Composition. Most writers believe that it is essentially an un-
coagulated conglomerate of irresoluble pearlite with ferrite in hypo- and cementite
in hyper-eutectoid steels respectively, but that it often contains some incompletely
transformed matter.
Occurrence. The transformation can be brought to the sorbitic stage (1) by re-
heating hardened steel to a little above 400 deg., but not to 700 deg. at which tem-
perature it coagulates into granular pearlite; (2) by quenching small pieces of steel
in oil or molten lead or even by air cooling them; (3) by quenching in water from just
above the bottom of the transformation range, An. Sorbite is ill-defined, almost amor-
phous, and is colored lighter than troostite but darker than pearlite by the usual
etching reagents. It differs further from troostite in being softer for given carbon
content, and usually in being associated with pearlite instead of martensite, and
from pearlite in being irresoluble into separate particles of ferrite and cementite.
As sorbite is essentially a mode of aggregation it cannot properly be represented
APPENDIX NOMENCLATURE OF THE MICROSCOPIC CONSTITUENTS 471
on the equilibrium diagram. Its components at all times tend to coagulate into
pearlite, yet it remains in its uncoagulated state at all temperatures below 400 deg.
Properties. Though slightly less ductile than pearlitic steel for given carbon
content, its tenacity and elastic limit are so high that a higher combination of these
three properties can be had in sorbitic than in pearlitic steels by selecting a carbon
content slightly lower than would be used for a pearlitic steel. Hence the use of
sorbitic steels, e.g. first hardened and then annealed cautiously, for structural pur-
poses needing the best quality.
Manganese Sulphide (Fr. Sulphur de Manganese, Ger^ Schwefelmangan), MnS
(Arnold and Waterhouse). Metaral.
Occurrence, etc. Sulphur combines with the manganese present in preference to
the iron, forming pale dove or slate gray masses, rounded in castings, elongated in
forcings.
Ferrous Sulphide (Fr. Sulphure de Fer, Ger. Schwefeleisen), FeS. Metaral.
Occurrence. The sulphur not taken up by the manganese forms ferrous sulphide,
FeS, which, probably associated in part with iron as an Fe-FeS eutectic, forms by
preference more or less continuous membranes surrounding the grains of pearlite.
Color, yellow or pale brown.
Sulphur Prints. When silk impregnated with mercuric chloride and hydrochloric
acid (Heyn's and Bauer's method) or bromide paper moistened with sulphuric acid
(Baumann's method) is pressed on polished steel, the position of the sulphur-bearing
areas, whether of FeS or MnS, records itself by the local blackening which the evolved
H 2 S causes. Phosphorus bearing areas also blacken Baumann's bromide paper.
MISCELLANEOUS
Eutectoid, Saturated, etc. The iron-carbon eutectoid is pearlite. Steel with more
carbon than pearlite is called hyper-eutectoid, that with less is called hypo-eutectoid.
Arnold's names "saturated," "unsaturated," and "supersaturated," for eutectoid,
hypo-eutectoid, and hyper-eutectoid steel respectively, have considerable industrial
vise in English-speaking countries, but are avoided by most scientific writers on the
ground that they are misleading, because, e.g. there is only one specific temperature,
AI, at which eutectoid steel is actually saturated, and, if any other temperature is in
mind, that steel is not saturated. Above AI it is clearly undersaturated.
The objection to the names sorbite, troostite, martensite, and austenite, that
each of them covers steel of a wide range of carbon content, is to be dismissed because
a like objection applies with equal force to every generic name in existence.
The theoretical matter in this report is given solely for exposition and the com-
mittee disclaims the intent to impose any theory. This report is offered for adop-
tion subject to this disclaimer on the ground that the adoption of theories is beyond
the powers of a Congress.
INDEX
A, AT, Ac, Ar 3 , Ac 3 , Ar 3 . 2 , Acs. 2 , Ar 3 . 2 .i, Ac 3 . 2 .i, Ar cm , Acc m . See critical points,
notation.
Allotropic theory of the hardening of steel, 87, 309
Allotropy, definition of, 106
of cementite, 192
iron, 106
Alloy steels. See special steels.
Alloys, constitution of, 407
, fusibility curves of, 411 to 427
, microstructure of, 411 to 427
of iron and carbon, equilibrium diagram of, 439 to 448
, fusibility curves of, 428 to 448
, phase rule applied to, 457 to 459
, structural composition immediately after solidification of,
429
, phase rule applied to, 454 to 459
, solidification of, 409 to 427
, structural composition of, 421 to 448
, whose component metals form solid solutions, solidification and constitution
of, 411 to 415
are insoluble in each other in the solid state, solid-
ification and constitution of, 415 to 423
partially soluble in each other in the solid state,
solidification and constitution of, 417 to 448
Alpha iron, 182, 207
, crystallization of, 107
, description of, 106
theory of the hardening of steel, 310
Alumina powder for polishing, preparation of, 52, 53
American ingot iron, 101
Amorphous cement vs. boundaries of crystalline grains, 91, 103
heat treatment of pure metals, 97
the straining of metals, 94
Anhedrons. See allotrimorphic crystals.
Annealing, air cooling in, 235
cold worked steel, 246
, cooling in, 233
, double treatment in, 240
for malleablizing cast iron, 401
, furnace cooling in, 235
, heating for, 231
, influence of maximum temperature in, 236
time at maximum temperature in, 239
, nature of operation, 231
of steel, 231 to 273
, oil and water quenching in, 239
'473
474 INDEX
Annealing, purpose of, 231
, rate of cooling vs. carbon content in, 234
size of objects in, 234
steel castings, 248
temperatures for steel, 233
Austenite, crystallization of, 215, 262
, definition, description, occurrence, and structure of, 277 to 280
, Osmond's test showing relative softness of, 281
, relative softness of, 286
, saturated, 429
Austenitic and pearlitic structures, relation between, 263
special steels, 332
steel, tempering of, 300
B
Baumann on sulphur printing, 45
Beilby on amorphous cement, 91, 94
Belaiew on the crystallization of steel and meteorites, 288 to 216
Benedicks' equilibrium diagram of iron-carbon alloys, 446
Beta iron, 183
, crystallization of, 107
, description of, 106
theory of the hardening of steel, 309
Binary alloys. See alloys.
Bismuth, crystalline grains of, 90
Bivariant equilibrium, definition of, 454
Black heart castings, 401
, annealing for, 402
Brittleness, intercrystalline, 271
, intergranular, 271
of low carbon steel, 271
Burnt steel, production and structure of, 259
C
Cameras, 27 to 33
Campion and Ferguson fusible alloy, 41
Carbide steel, 326
Carbon, condition of, in hardened and tempered steel, 305
, hardening and combined in steel, 305
in pearlite, 131
in steel, 119
solubility in iron, 364
temper, 398
theory of the hardening of steel, 310
Carpenter and Keeling's cooling curves of steels, 167
determinations of the critical points, 167
equilibrium diagram of iron-carbon alloys, 445, 446
Case hardened articles, heat treatment of, 324
steel, tempering of, 325
hardening by gas, 319
, composition of iron or steel subjected to, 315
, cooling after, 324
, distribution of carbon after, 316
, duration of, 316
, materials used for, 318
, mechansim of, 322
of steel, 315 to 325
INDEX 475
Case hardening, temperatures for, 315
Cast iron, calculation of structural composition of, 370, 375, 394
, chilled castings of, 378
, constitution, properties, and structure of, 304 to 397
containing only combined carbon, 369
graphitic carbon, 366
, eutectic, 379, 381
, formation of combined and graphitic carbon in, 366
, impurities in, 386 to 397
, influence and occurrence of manganese in, 387
phosphorus in, 388
silicon in, 386
sulphur in, 386
, malleable, 398-406
, solidification and cooling of, 381
, structural composition vs. physical properties of, 378
steel, structure of, 208 to 220
Castings suitable for malleablizing, 399
Cement carbon, definition of, 122
Cementation. See case hardening.
'o! iron and steel, 315 to 325
Cementite, allotropy of, 192
, definition and description of, 122
, etching of, 131
, free, definition of, 129
, graphitizing of, 257, 384, 398
in high carbon steel, 128
, primary. See cementite, pro-eutectic.
, pro-eutectic, 432
, spheroidizing of, 252
Cementitic special steels, 326, 333
Chilled castings, 378
Chrome-nickel steel, 353
steel, 349
, uses and properties of, 349
-tungsten steel. See high-speed steel.
Chromium, influence on critical points of iron of, 349
Cleavage, brittlenoss. See intercrystalline brittleness.
definition of, 86
Cold working, crystalline growth after, 96
, influence on structure and properties of steel of, 227
Colloidal solution, 285
Components, definition of, 454
Condensers, 26, 27
Cooling and heating curves of iron and steel, 169 to 181
curves of pure metals, 407
Copper, microstructure of, 86
, twinnings in, 95
Critical points and crystallization, 200, 204
dilatation, 199
electrical conductivity, 200
magnetic properties, 203
, calorimetric method for determination of, 179
, Carpenter and Keeling's determination of, 167
, causes of, 182 to 198
, definition of, 158
, determination of, 169 to 181
, graphical representation of the position and magnitude of, 169
476 INDEX
Critical points, heat absorbed or evolved at, 167
in high carbon (hyper-eutectoid) steel, 166
iron, description of, 163
medium high carbon steel, 165
pure iron, 163
very low carbon steel, 164
, influence of chemical composition on position of, 162
speed of heating and cooling on, 161, 162
, magnetic method for determination of, 179
, melting-points method for determination of, 179
, merging of, 165, 167
, metallographic method for determination of, 179
, minor, 167
, notation, 159
, occurrence of, 159 to 181
, relation between structure of steel and, 195
, their effects, 199 to 207
, thermo-electric method for determination of, 179
, use of neutral bodies in detecting, 173
range. See critical points,
temperatures. See critical points.
Crystalline grains. See grains.
growth in metals on annealing, 96
of strained ferrite, 265 to 271
Crystallite of iron, 105
Crystallites, definition of, 87
Crystallization and critical points, 200, 204
, cubic, of metals, 90
of austenite, 208
iron, 103
steel, 208
, process of, 86, 87
Crystallography, systems of, 91
Crystals, allotrimorphic, definition of, 87
, cubic, of iron, 103
, definition of, 86
, formation of, 86
, idiomorphic, definition of, 87
, mixed. See mixed crystals.
Cubic crystallization of iron, 103
metals, 90
Degrees of freedom, definition of, 452
liberty. See degrees of freedom.
Desch's types of cooling curves, 177
Dilatation and critical points, 199
Divariant equilibrium. See bivariant equilibrium.
Ductility of steel, structural composition vs., 141
E
Electric arc lamps, 23 to 27
furnaces, 39
Electrical conductivity and critical points, 200
Electrolytic iron, crystallizing properties of, 111, 112
microstructure of, 101
Electromagnetic stages, 15
INDEX 477
Equilibrium, bivariant, definition of, 454
, definition of, 452
diagram. See fusibility curves.
of iron-carbon alloys, 439 to 448
, Benedicks' diagram, 446
, Carpenter and Keeling's diagram, 445
, Roberts-Austen's diagrams, 442, 443
, Roozeboom's diagram, 444
, Rosenhain's diagram, 447
, Ruff's diagram, 449
, the author's early diagram, 441
, Upton's diagram, 448
, Wittorff's diagram, 450
, metastable, definition of, 453
, stable, definition of, 452
, univariant, definition of, 454
, unstable, definition of, 453
, unvariant, definition of, 454
Ktching, 42,_43, 62, 64
figures. See etching pits,
for macrostructure, 47
of cementite, 43, 131
wrought iron, 45
pits, formation of, 90
in iron, 46, 104
nitric acid, 42
picric acid, 42
sodium picrate, 43
Stead's reagent, 43
Kutcctic alloys, 99, 120
, constitution and occurrence of, 415 to 427
, definition of, 418
, cast iron, 379
, iron-carbon, 429
Eutectoid, definition of, 121
steel, definition and structure of, 126, 127
Ewing and Rosenhain, straining of iron by, 110
metals, 92
Rosenhain's theory of crystalline growth of metals on annealing, 96, 97
F
1'errite, crystalline growth of, 265
, definition of, 104
, free, 121
in cast iron, 367
low carbon steel, 1 19
wrought iron, 114
Fibers in wrought, iron, llo
Finishing temperatures, influence on the structure and properties of steel of, 223
Free cementite, definition of, 129
ferrite, 121
Furnaces, electric, 39
Fusibility curves of alloys, 411 to 427
iron-carbon alloys, 428 to 450
G
Gamma iron, 182, 207
, crystallization of, 107
478 INDEX
Gamma iron, description of, 106
, twinning in, 107
Ghost lines in steel, 153 to 157
Grading of steel vs. its carbon content, 118
Grain refining treatment, 241
Grains, crystalline orientation of, 90
, ferrite, 102
, orientation of, 102
, growth of, on annealing, 96
of metals, definition and formation of, 89
, heterogeneousness of, 89
Graphitic carbon, factors influencing formation of, 366
in cast iron, 366
Graphitizing of cementite, 257, 384, 398
in malleablizing cast iron, 398
Granulation of steel, 209
Gray cast iron, 366
vs. malleable cast iron, 406
Guillet's theory of special steels, 326
H
Hadfield steel.. 345
Hard castings, 399
Hardened and tempered steel, microstructure of, 304
Hardening and tempering in one operation, 297, 299
carbon, definition of, 305
theory of the hardening of steel, 311
, cooling for, 275
, heating for, 274
of steel, 274 to 297
, theories of, 308 to 314
, structural changes on, 276
theories of the hardening of steel, classification of, 308
Hardenite, definition, occurrence, and properties of, 291
Heat tinting, 44
treatment of case hardened articles, 324
iron, influence of, 110, 111
metals, influence of, 96
Heating and cooling curves of iron and steel, 169 to 181
High-speed steel, 354 to 363
, composition of, 355
, discovery by Taylor and White of, 354
, etching of, 47, 361
, heating and cooling curves of, 357 to 361
, microstructure of, 355
, properties of, 354
, theory of, 356
, treatment of, 354
Hot working, influence on structure and properties of steel of, 221 to 225
Hyper-eutectoid steel, definition and structure of, 127
Hypo-eutectoid steel, definition and structure of, 127
I
Idiomorphic crystals, definition of, 87
Igevsky, picric acid etching, 42
Illumination for microscopical work, 18 to 27
Illuminators, vertical, 20 to 22
Impurities in cast iron, 386 to 397
INDEX 479
Impurities, in metals, influence of, 97 to 100
steel, 143 to 157
, segregation of, 153
influence on iron of, 112
Ingot iron, 101
Ingotism, 220
Intercrystalline brittleness, 271
Intergranular brittleness, 271
Interstrain theory of the hardening of steel, 313
Invar (nickel steel), 343
Inverted microscope, 31 to 33
Iris diaphragms, 11
Iron, affinity for carbon of, 315
, allotropy of, 106
, alpha, 182, 207
, description of, 108
, beta, 182, 207 *
, description of, 108
-carbon alloys, equilibrium diagram of, 439 to 450
, fusibility curves of, 428 to 450
, phase rule applied to, 455 to 459
, structural composition immediately after solidification of, 430
eutectic, 429
, cementation of, 315 to 325
-cementite fusibility curve. 428
, cooling and heating curves of, 169 to 181
, critical points of, 163, 182
crystallite, 104
, crystallization of, 102, 107
, crystallizing of, 111, 112
, cubic crystals of, 103, 104
, electrolytic, microstructure of, 101
, etching in hydrogen, 117
pits in, 104
, gamma, 182, 207
, description of, 108
-graphite fusibility curve, 434
, influence of chromium on critical points of, 349
heat treatment of, 110, 111
impurities on, 112
mechanical treatment of, 110
nickel on dilatation of, 343
tungsten on critical points of, 346
, microstructure of, 101
oxide in steel, 153
, slip bands in, 110
, straining of, 92
sulphide in steel, 146
Irreversible steels, 337
Isomorphous mixtures, definition of, 98
K
Kourbatoff's etching to color cementite, 43
reagent for hardened steels, 63, 280
L
Le Chatelier's inverted microscope, 67 to 71
Ledebur's temper carbon, 398
480 INDEX
Lieberkuhn, 20
Lights for microscopical work, 18 to 27, 50
Liquidus, definition of, 410
M
Macrostructure, etching for, 47
Magnetic properties and critical points, 203
method for determination of critical points, 179
specimen holders, 12
Magnifier, vertical, 23
Malleable cast iron, 398 to 406
, annealing for the manufacture of, 400
, packing materials for the manufacture of, 400
vs. gray cast iron, 406
castings. See malleable cast iron.
Manganese in cast iron, influence and occurrence of, 387
steel, 148
oxide in steel, 150
steel, 343 to 346
, austenitic, 345
, martensitic, 345
, pearlitic, 344
, water-toughening of, 345
sulphide in steel, 145, 151
Manipulations, 40 to 50
Martensite, definition, description, occurrence, properties, etching, and structure of, 283
Martensitic special steels, 332
steel, tempering of, 302
Matweieff's etching to color cementite, 43
method of etching slag in wrought iron, 1 17
Maurer, production of austenite by, 279
Mechanical refining, 229
stages, 8
treatment of iron, influence of, 110
metals, influence of, 96
steel, 221 to 225
Metallic alloys. See alloys.
, constitution of, 407 to 427
Metallographic laboratory, apparatus for, 5
Metallography, industrial importance of, 1
Metalloscope, universal, 14 to 18
Metals, cooling curves of, 407
, crystalline growth on annealing, 96
, crystallization of, 87
, cubic crystallization of, 90
, definition and formation of grains of, 89
, influence of heat treatment, 96, 97
mechanical treatment of, 96
, latent heat of solidification of, 408
, phase rule applied to, 455
, solidification of, 407
Metarals, definition of, 293
Metastable equilibrium, definition of, 453
Meteorites, microstructure of, 212
Microscopes and accessories, 5, 67 to 85
, inverted, 31 to 33, 67
Microstructure of cast steel, 208 to 220
electrolytic iron, 101
INDEX 481
Microstructure of hardened and tempered steel, 304
high carbon steel, 126
sulphur steel, 145
impure gold, 99
low carbon steel, 119
medium high carbon steel, 124
meteorites, 212
pure copper, 86, 89
gold, 86
iron, 101
metals, 86
worked steel, 221 to 230
wrought iron, 113 to 117
Mixed crystals, definition of, 98
Mohs scale of hardness, 123
Molybdenum steel, 351
Monovariant equilibrium. Sec univariant equilibrium
Mottled cast iron, 375
N
Nachet illuminating objectives, 22
prism vertical illuminator, 21
Nernst lamp, 25
Neumann's lines, 96, 109
Neutral bodies for the detection of critical points, 173
Nickel, influence of, on critical points of iron, 337
dilatation of iron, 343
steel, 336 to 343
, austenitic, 342
, case hardening of, 342
, critical points of commercial, pearlitic, 339
, hardening and annealing of, 339
, martensitic, 342
, pearlitic, 337
, properties of pearlitic, 338
Nitric acid etching, 42
Non-variant equilibrium. See unvariant equilibrium
O
Objectives, 8
Orientation of crystalline grains, definition of, 90
ferrite grains, 102
Osmond,' and Cartaud on the crystallization of iron, 107, 108
, on polishing, 51, 61
, production of austciiite by, 277
Osmondite, definition, description, and occurrence of, 303
Overheating, 258 ,
P
Parabolic reflector, 20
Patented wire, 247
Patenting, 247
Pearlite, carbon content of, 131
, definition and description of, 120
, formation of, 190
in high carbon steel, 126
low carbon steel, 120
, varieties of, 256
482 INDEX
Pearlitie special steels, 331
Phase rule applied to alloys, 454
iron-carbon alloys, 457
metals, 455
, definition of, 454
, enunciation and explanation of, 452
Polymorphism, 1()ti
Phosphorus in cast iron, influence and occurrence of, 388
steel, 144
Photography. See photomicrography.
Photomicrographic cameras, 27 to 33
Photomicrography, 48
Picrate of sodium etching, 43
Picric acid etching. 42
Pits. See etching pits.
Planes of cleavage. See cleavage.
Platinite (nickel steel), 343
Point of recalescence. See recalescence point.
Polishing, 40, 41, 51 to 62
machines, 34, 35, 51 to 61
Polyhedral special steels, 326, 332
Polymorphism. See allotropy.
Portevin's etching for macrostructure, 47
Potentiometer, 36
Preserving samples. 64
Prism vertical illuminator, 21, 84
Pseudomorphism, definition of, 304
Pure metals, crystallization and microstructure of, 86
Pyrometer, Lc Chatelier thermo-electric, for the determination of the critical points, 36
Pyrometers, 36
, self-recording, 37 to 39, 178
Q
Quaternary steels, 335. See also special steels,
vanadium steels, 340
Quenching in annealing, 240
Recalescence point, description and occurrence of, 158
Red-shortness in steel caused by sulphur, 147
Refining, mechanical, 229
Retardations. See critical points.
Retention theories of the hardening of steel, 308
Reversible steels, 337
Revillon on preparation of alumina for polishing, 53
Roberts-Austen's equilibrium diagrams of iron-carbon alloys. 444
use of neutral bodies for detecting critical points, 39, 173
Robin, 'on preparation of alumina for polishing, 53
production of austenite by, 278
Rohl on sulphur printing, 45
Roozeboom's equilibrium diagram of iron-carbon alloys, 444
Rosenhain and Ewen, on amorphous cement, 91
Ewing. See Ewing and Rosenhain.
Humfrey, straining of iron by, 110
Rosenhain's equilibrium diagram of iron-carbon alloys, 447
Ruff's equilibrium diagram of iron-carbon alloys, 449
INDEX 483
Saladin self-recording pyrometer, 37 to 39
Saladin's cooling and healing curves of steels, 175
Segregation of impurities in steel, 153
Self-hardening steel, 348
-recording pyrometers, 37 to 39, 178
Silicates in steel, 150
Silicon in cast iron, influence and occurrence of, :>sii
steel, 143, 144
steel, 352
Slag in wrought iron, 114, 110, 117
, composition of, 11G
Matweieff's method of etching, 117
, microstructurc of, 116
Slip bands, description and production of, 92
in iron, 110
Sodium picrate etching, 43
Solid solutions, 409
, definition of, 98
Solidus, definition of, 410
Solution theories of the hardening of steel, 309
Sonims, 143. 150
Sorbitc, definition, description, and formation of, 225, 230, 289
Sorby-Beck parabolic reflector. 20
Special steels, 326 to 363
, austcnitic, 332
, cementitic, 333
, constitution, properties, treatment, and uses of most important types,
320 to 335
, definition and general character of, 326 to 335
, influence of special elements on position of critical range in, 328
, martensitic, 332
. pearlitie, 331
, polyhedral, 332
, treatment of, 333
Specimen holders, 11 to 11
Spheroidizing of cementite, 252
Stable equilibrium, definition of, 453
Stages, electromagnetic, 15
, leveling 60
, mechanical, 8
Stead and Carpenter on the crystallizing properties of electrolytic iron, 111, 112
on heat-tinting, 44
phosphorus in cast iron, 388 to 392
the briulcness of low carbon steel, 271
crystalline growth of very low carbon steel, 265
on polishing, 53 to 55
Steadite, definition and description of, 390
Stead's brittlcness, 273
etching reagent for detection of phosphorus, 43
Steel, annealing of, 231 to 273
, temperatures of, 232
, brittlenesis of low carbon, '271
, burning of, 259
, calculation of structural composition of, 132, 148
, carbon in, 119
, case hardening of, 315 to 325
484 INDEX
Steel castings, annealing of, 248
, causes of critical points in, 182 to 198
, cementation of, 315 to 325
, chemical tests for the detection of sulphur in, 44, 45, 148
vs. structural composition of, 134, 148
, chrome, 349
-nickel, 353
, constitution, properties, treatment, and uses of most important types of special,
33(i to 363
, cooling and heating curves of, 169 to 181
, critical points of, 158 to 207
, crystallization of, 208
, ductility vs. structural composition of, 141
, effects of critical points in, 199 to 207
, eutectoid, definition and structure of, 126, 127, 216
, formation of graphite in high carbon, 257
, ghost lines in, 153 to 157
, grading of, 118
, hardening of, 274 to 297
, high carbon, cementite in, 127 to 131
, microstructure of, 126 to 131
, pearlite in, 126
-speed, 354 to 363
, etching of, 47
, hyper-eutectoid, definition and structure of, 127, 218
, hypo-eutectoid, definition and structure of, 129, 216
, impurities in, 143 to 157
, influence of cold working on the structure and properties of, 227
finishing temperatures on the structure and properties of, 223, 229
hot working on the structure and properties of, 221
, iron oxide in, 153
sulphide in, 146
, irreversible, 337
, ferrite in, 119
, microstructure of, 119 to 121
, pearlite in, 120
vs. wrought iron, 118
, manganese, 343 to 346
in, 148
oxide in, 152
sulphide in, 145, 151
, maximum strength of, 140
, mechanical refining of, 229
treatment of, 221 to 225
, medium high carbon, microstructure of, 124, 125
, micro-test for determination of carbon in, 135
, pearlite in, 124
, nickel, 336 to 343
, normal structure of, 118
, occurrence of critical points in, 158 to 181
of maximum hardening power, 296
overheated, 259
phosphorus in, 144
, physical properties of constituents of, 137
, production and structure of burnt, 259
, relation between structure above and below the critical range of, 262
and critical points of, 195
, reversible, 337
INDEX 485
Steel, segregation of impurities in, 153 to 157
, self-hardening, 34-S
, silicates in, 150
, silicon, 352
in, 142, 143
, special, 326 to 363
, structural changes on cooling in, 187
composition of, 132, 133
, structure of cast, 208 to 220
worked, 221 to 230
, sulphur in, 145, 151
, tempering of hardened, 298 to 306
, tenacity vs. structural composition of, 138 to 140
, theories of hardening of, 308 to 314
, tungsten, 346
, vanadium, 349
vs. carbon content, grading of, 118
, \\idmanstatten structure in, 212
Straining of iron, 92, 110
, crystalline growth after, 96
of metals, 92, 94
Stress theories of the hardening of steel, 311
Structural composition of alloys, 221 to 226
cast iron, calculation of, 370, 375, 395
iron-carbon alloys immediately after solidification, 430
steel, calculation of, 92, 132 to 134'
Subcarbide theory of the hardening of steel, 311
Sulphur in cast iron, influence and occurrence of, 388
steel, 145
, chemical tests for the detection of, 44, 45, 151
printing, 44, 45, 148
Taylor and White's discovery of high-speed steel, 354
Temper carbon, 398
Temperatures for annealing steel, 232
Tempering and the retention theories of the hardening of steel, 313
stress theory of the hardening of steel, 313
colors, 298
, decrease of hardness on, 306
, explanation of, 298
, heat liberated on, 307
, influence of rate of cooling in, 299
time in, 299
of austenitic steel, 300
case hardened steel, 325
hardened steel, 298 to 306
martensitic steel, 302
troostitic steel, 302
temperatures, 298
Tenacity of steel vs. structural composition, 138 to 140
Ternary steels, 326. See also special steels.
Thermal critical points. Sec critical points.
treatment. See heat treatment.
Toughening treatment, 241
Transformation points. See critical points,
range. See critical points.
486 INDEX
Transition const it uents. See also martensite, troostite, and sorbite.
, definition and formation of, 293
Troostite, definition, description, occurrence, properties, etching, and structure of, 285
Troostitic steel, tempering of, 302
Troosto-sorbite, 290
Tschernoff iron crystallite, 105
Tungsten, influence on the critical points of iron of, 346
steel, :;iii
Twinnings, and amorphous iron theory, 313
definition of, 95
in copper, 95
gamma iron, 107
marble, 94
produced by pressure, 95
> U
Univariant equilibrium, definition of, 454
Universal metalloscope, 14 to 18
Unstable equilibrium, definition of, 453
Unvariant equilibrium, definition of, 454
Upton's equilibrium diagram of iron-carbon alloys, 448
Vanadium steel, 349, 353
Vertical illuminators, 18 to 23
magnifier, 23
W
Water-toughening of manganese steel, 345
Welsbach lamp, 23
Widmanstatten structure, 212
Wittorff's equilibrium diagram of iron-carbon alloys, 450
White, cast iron, 369
heart castings, 401
, annealing for, 401
Maunsel. See Taylor and White.
Workshop microscopes, 81 to 84
Wrought iron, composition of, 113
, definition of, 113
, etching of, 45
, fibers in, 115
, microstructure of, 114 to 116
, slag in, 114, 116, 117
vs. low carbon steel, 118
Y
Yatscviteh, M., etching of high-speed steel, 47
Z
Zciss prism illuminator, 21
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