Fracture Toughness dynamic fracture toughness .

The irons have microstructures

comprising a matrix ranging from predominantly austenitic
to predominantly martensitic and numerous large M 7C3 car-

of White bides.

EXPERIMENTAL PROCEDURE
Cast Irons The experimental approach used a compositional grid that
provided a wide variation in the quantity of M 7C3 carbides
in a matrix of constant composition and of enough harden-
ability to prevent transformation of the austenite to pearlite
either during mold cooling or during air cooling after reheat-
K. H. Zum Gahr ing to various austenitizing temperatures. Twelve heats were
Ruhr-University of Bochum produced to provide a variation in carbide volume from about
West Germany 10% to 50%. One additional heat was made to provide enough
iron of constant carbide volume to determine the effect on
fracture toughness of a range of matrix microstructures ob-
William G. Scholz tained by a wide range of heat treatments.
Climax Molybdenum Company of Michigan
Ann Arbor, Michigan Material Preparation
Thirteen high-Cr/Mo white cast irons, with varying carbon
and chromium contents, were cast from induction-melted
heats. All heats were cast as 50-mm Y-blocks in baked sand
molds. The chemical compositions of the heats are given in
Table I.
SUMMARY Heat Treatment
The volume of the massive (primary and/or eutectic) Specimen blanks were cut from the Y-blocks with a tung-
carbides and the structure of the matrix influenced fracture sten carbide band saw and heat treated in an electric furnace
toughness of high-Cr/ Mo white cast irons. K lc fracture
toughness of structures with more than 30% carbides and
KId fracture toughness over the whole range of carbide vol-

umes (7-45%) decreased with increasing volume of carbides.

However, there was no significant difference either in K lc
values of the austenitic irons or of the martensitic irons
when the carbide volumes were in the range of 7% to about
20-30%.
At a constant carbide volume of 28%, some tempered
austenitic structures had greater KId values than any of the
martensitic structures. Martensitic structures, however, cov-
ered about the same range of K lc values as austenitic struc-
tures. At comparable stress-relieving heat treatments, mar-
tensitic structures generally had larger K lc values than
austenitic structures.

INTRODUCTION
High-chromium white cast irons are extensively used for
mining and milling service because they exhibit exceptional
abrasion resistance if the microstructure is properly con-
trolled. One example l of the use of large castings of high-
chromium white irons is the large autogenous grinding mill
for taconite ore shown in Figure 1. The shell liners and lift-
er bars are cast from high-chromium/ molybdenum white
iron. Wear rates of liners per ton of ore decreased 33% com-
pared to quenched-and-tempered martensitic steel formerly
used in this mill. Other applications include impact crush-
ers for limestone and cement clinker and rod mills for grind-
ing copper ore. Another important and increasing applica-
tion for high-chromium white irons is in rolling-mill rolls,
specifically those used for continuous hot rolling of steel
plate and strip.
It is evident from these applications that alloyed white
irons possess adequate toughness for quite severe service,
although no correlation has yet been established between
various toughness test results and the toughness required
for any service application. It appears that fracture tough-
ness measurements might give the desired correlations, and
attempts have recently been made to determine fracture
toughness of abrasion-resistant irons. 2 - 7 Fracture toughness
values were found to be in the same range as those deter-
mined for tool steels. 8 - 11 The purpose of this study was to Figure 1. Feed end liners In 11-m diameter autogenous mill
determine the influence of both carbide volume and matrix for grinding highly abrasive taconite ore. Hlgh-Cr / Mo Irons are
microstructure on toughness, in terms of both static and used for lifter bars and shell liners.

38 JOURNAL OF METALS. October, 1980

 Table I: Chemical Composition (Wt. %) and Massive Carbide Volume of High-Cr / Mo Irons

Element, % Carbide
Heat Volume,
No. C Si Mn Cr Mo Cu Ni P S %
17A 1.41 0.58 1.56 11.6 2.39 1.24 0.020 0.D18 0.030 7.1
17B 1.38 (0.58)* (1.56) 12.8 (2.39) (1.24) (0.020) (0.018) (0.030) 9.8
18A 2.00 0.59 1.54 15.8 2.35 1.14 0.020 NA** NA 14.4
18B 1.89 (0.59) (1.54) 17.8 (2.35) (1.14) (0.020) NA NA 17.4
16A 2.58 0.56 1.50 17.6 2.39 1.03 0.023 0.020 0.030 24.3
16B 2.48 (0.56) (1.50) 18.7 (2.39) (1.03) (0.023) (0.020) (0.030) 22.7
19A 2.87 0.58 1.52 20.0 2.36 0.94 0.020 NA NA 29.1
19B 2.79 (0.58) (1.52) 21.0 (2.36) (0.94) (0.020) NA NA 30.4
63 2.92 0.57 1.55 19.0 2.35 0.94 0.04 0.032 0.025 28.0
20A 3.50 0.61 1.59 23.4 2.47 0.87 0.022 0.020 0.030 37.6
20B 3.41 (0.61) (1.59) 24.1 (2.47) (0.87) (0.022) (0.020) (0.030) 41.1
21A 3.93 0.63 1.57 24.6 2.45 0.76 0.022 NA NA 45.4
21B 3.81 (0.63) (1.57) 25.7 (2.45) (0.76) (0.022) NA NA 38.8

·Values in parentheses were not analyzed but are assumed to be the ssme 88 those obtained on analysis of the "A" ingot of the same heat.
"Not analyzed.

with no protective atmosphere. Some specimen blanks from Table II:

each heat were stress relieved 200°C /2 h to test austenitic Summary of Heat Treatment Conditions for Heat 63, Containing
structures. For martensitic structures, specimen blanks were 2.9% C, 0.6% Si, 1.5% Mn, 19.0% Cr, 2.4% Mo, and 0.9% Cu
austenitized 9OO°C/5 h and forced-air cooled to room tem-
perature. These specimen blanks were then refrigerated twice
to -78°C in dry ice and methanol, and stress relieved REDOMINANTLYAUSTENITI PREDOMINANTLY MARlENSITIC
200°C/2 h. STRUCTURES STRUCTURES
The influence of the matrix structure on fracture toughness
was studied using specimens from Heat 63 only (see Table
I). Variations in matrix structure were obtained by the heat I CD As·Cast I
treatments listed in Table II.
CD 1120°C/4h ~ f- eD 1()()()OC/24h
Microstructure Analysis @ + 200°C/2h Furnace Cooled to 950°C
The volume of carbides in the microstructures of all 13 + 950°Cllh
heats was determined by computerized image analysis, using @ 200°C/2h I---
an Imanco Quantimet 720. Fifty areas on each specimen r-e CD l()()()OC / 4h
were examined at a microscopic magnification of 250X. A @ 250°C/2h
statistical analysis of the volume of massive carbides @ +200°C/2h
(primary and/ or eutectic carbides) used the values of the 50 ® 330°C/2h @ +250°C/2h
areas counted for each heat. The amount of retained aus-
tenite in selected microstructures was measured by an x-ray ® 4OO°C/2h @ +330°C/2h
diffraction method devised for alloy cast irons.12 @ +400°C/2h
® 550°C/2h @ +550°C/2h
Fracture Toughness CD 550°CIlOh @ +500°C/3h
Methods for measuring the fracture toughness values of
relatively brittle materials such as white cast irons have been @ 550°C/20h @ +500°C/10h
described in the literature. 4 •6 For determining static
fracture toughness (K[c) in this work, 12.5-mm-thick com-
@ 550°C/5h ® +500°C/20h
pact tension specimens were machined by grinding and @ 620°C/2h ® +500°CIlOh
+ 250°C/2h
notched by electrical discharge machining (EDM). The
specimens were precracked using a fatigue machine with a
loading cycle of P min = 350-450 Nand P max = 4600 N, at 30
® 700°C/2h
@ 950°C/4h
Hz. The precracked specimens, with a crack length of at least .. @) +200°C/2h
2 mm, were fractured under load control with a loading rate
of 17.8 kN / min using servohydraulic testing equipment. The
K[c fracture toughness was calculated according to ASTM
standard test procedure E399-78.
ri@ l()()()OC / 4h
+2 x 0.25 h at -78°C
The dynamic fracture toughness, K[d, was measured using
an impact test machine with an instrumented Charpy @ 9OO°C/4h
tup. The specimens, measuring 10 X 10 X 55 mm,were notch- r. ® +200°C/2h
ed by electrical discharge machining a O.2-mm radius slot 2
mm deep. The hammer of the testing equipment had a veloc-
ity of 1.23 m/ s at impact. Load and energy as a function of ® 1035°C/4h
+200°C/2h
time were recorded during each test. The fracture load was
JOURNAL OF METALS· October, 1980 39
 (3) (b) (c) (d)

Figure 2. Microstructures of experimental Irons: (a) as-cast Heat 18A (2.0C-15.8Cr-2.4Mo-1.1Cu), 14.4% carbides; (b) as-
cast Heat 19A (2.9C-20.0Cr-2.4Mo-0.9Cu), 29.1% carbides; (c) as-cast Heat 21A (3.9C-24.6Cr-2.4Mo-0.8Cu), 45.4% carbides;
and (d) heat-treated martensltlc Heat 17A (1.4C-11.6Cr-2.4Mo-1.2Cu), 7.1% carbides.

used to calculate KId values using the equation for three- EXPERIMENTAL RESULTS
point-bend specimens according to ASTM E399-78. An in- Influence of Carbide Volume
house investigation had previously shown that the difference
in calculated KId values between precracked and EDM- Microstructure. Figure 2 shows examples of microstructures
notched specimens is about 1-2 MPay'ffi. Therefore, we of the white cast irons used in this study. The as-cast irons
believe that EDM notch geometry is sufficient to lead to were predominantly austenitic (Figures 2a-2c) with this vol-
reliable results for the relatively brittle white irons. ume of massive carbides (primarily and/ or eutectic carbides)
All reported K l c and KId fracture toughness values are the varying between 7 and 45%. The carbides, examined by
average of at least two, and in a few cases three or four, test microprobe analysis, were found to be of the type (Cr.Fe3)C3.
values. The fracture toughness testing was carried out in air Their shape changed from eutectic networks between the
at 50% relative humidity and 21°C as average conditions. austenite dendrites (Figure 2a) for Heats 10, 17, and 18 to
The Vickers hardness of each specimen was measured lamellar or radial (Figure 2b) for Heats 19 and 63. The
using a 50 kg load. In addition to mechanical testing, change from one carbide morphology to the other occurred as
fracture surfaces of selected K lc and KId specimens were a slow transition in the carbide shape as the carbon plus
investigated in an AMR-l000 scanning electron microscope. chromium content (i.e. the carbide volume) increased. Pri-
The amount of carbide on fracture surfaces was measured by mary hexagonal carbide rods (Figure 2c) in addition to lamel-
using the linear intercept method on electron micrographs. lar and/ or radial eutectic carbides occurred in Heats 20
and 21.
Heat treatments of the as-cast irons between 900°C and
1035°C resulted in the austenite being depleted of carbon
due to the precipitation of secondary carbides (~0.5-1
9oor-----,-----r----r----r------.
• MARTENSITIC ~m, Figure 2d) . Consequently, much of the austenite trans-
• • AUSTENITiC formed to martensite during cooling to room temperature.
LO
C\I
The amount of austenite remaining in the structures at room
5: 800
temperature was reduced by refrigerating twice to -78°C.
Heating at 200°C /2 h was designed to reduce internal
iii
rn
Q)
stresses of the structures.
c: Hardness and Fracture Toughness. Figure 3 shows how the
"0
:u
.r; 700
increase in carbide volume raised the bulk hardness of pre-
o dominantly austenitic and predominantly martensitic struc-
U tures. The hardness of the martensitic structures was, as
~ expected, substantially greater than that of the austenitic
"0
~ 600
structures. The microhardness of the austenitic matrices
was about 410 HV 25 for all heats, and was independent
~ of carbide volume.
>
J: AUSTENITIC Figure 4 shows the influence of carbide volume on the K lc
gf 500 and KId fracture toughness- of the different irons in the
Q)
c: austenitic and the martensitic conditions. K l c fracture tough-
"0
:u • • ness values were found to be much the same with increasing
J: • 16B
1~ _ _ _ ._-4-- __
• HV25 carbide volume up to about 20% or 30% for the austenitic and
martensitic structures (Figure 4a) . For carbide volumes up
•
.)t!
"5 400
•• to 30%, the K l c values were substantially greater for the
•
al
• austenitic structures than for the martensitic structures at
the same carbide volume. K l c fracture toughness values were
determined to be about equal in the austenitic and mar-
3000~----~1~0------~2~O--~--~3~0------~4~0------~50
tensitic structures with carbide volumes greater than 30%.
VOLUME PERCENT CARBIDE Beyond a carbide volume of 30%, there was a marked de-
Figure 3. Relationship between hardness and carbide volume crease in the K l c values with increasing carbide volume (Fig-
for austenitic structures (as-cast + 200°C 1 2h) and martensitic ure 4a) .
structures (900°C / 5h, cooled by forced air, refrigerated twice KId values decreased with increasing carbide volume over
to -78°C, and stress relieved 200° C / 2h). the range of carbide volumes investigated (Figure 4b) . At

40 JOURNAL OF METALS· October, 1980

 35
AS·CAST + 2 HOURS AT 2O-700·C
~ AUSTEHITIC 34

~
30 A---
17A

.17B
18B
18A..
16B
.......
.63
•
19B
32

ftII
D-
2
"-
16B. ~9iA19B
.!.!
lII:: 25
17AA
A
A
A 16A. A 9A
63
~ftII
30

D-
...
vi
CD MARTENSlTIC 2
~
28
c:
-&.
:::I
:!!
lII::
~ 20 .!.!
26
!:::I ~
1$ ......
I!
LI.
CD
c: 24 900
..c:
III
:::I
15
.....
0
22 800
!:::I
0 10 20 30 40 50 1$
Carbide Volume, % I!
LI. 20 700 ~
:z:
(a) Static Fracture Toughness
Ii
!iii!

L --'"
600 ~
HV50 ~
35
-- --4.,. 'y...._.6-~- "
16 '6..._ ..
500

~ftII
30 14
0 100 200 300 400 500 600 100
400
D-
::E Tempering Temperature, °C
:!!
lII::
(a) As-Cast Austenitic Structures
...vi
CD
25

c:
..c:
III

~ 34
! 20
~
I!
LI.

15

o 10 20 30 50
Carbide Volume, %
(b) Dynamic Fracture Toughness
Figure 4. Static. (a) and dynamic (b) fracture toughness of .!.!
austenitic and martensltlc matrix irons as a function of volume ~
of massive carbide. Austenitic Irons were as-cast, stress-
relieved 200°C/2h; martensltlc Irons were heat treated i
..c:
24 900
900° C/5h, refrigerated twice at -78°C, and stress relieved
200° C/2h. 1
~ 22 800

a given carbide volume, the austenitic matrix exhibited 700 ~

greater KId values than the martensitic matrix. :z:

'"
Influence of the Matrix Structure 600 '"
~
'"~
Microstructures. The matrix structure of Heat 63, obtained
by the heat treatments listed in Table n, can be categorized 500
as predominantly austenitic or predominantly martensitic.
The volume of massive carbides, about 28%, was constant for
all derived matrix microstructures. Hereafter, heating as-cast 400
300 400 500 600 100
or quenched specimens to 200° will be referred to as stress reo
lieving, and heating specimens above this temperature but Tempering Temperature, °C
below the eutectoid temperature will arbitrarily be referred
to as tempering. However, heating the austenitic as·cast (b) Martensitic Structures (4 Hours at lOOO°C)
structure up to about 400°C for 2 h resulted mainly in stress
relieving and mild tempering of the martensite present Figure 5. Fracture toughness and hardness resulting from tem-
(about 24% of the matrix) in the structure. The amount of pering .Heat 63 for 2 11: (a) as-cast austenitic structures,
austenite in the matrix decreased slightly from 76% to 20-700°C, (b) martensitlc structures, 1000°C.

JOURNAL OF METALS. October, 1980 41

about 69% due to heating between 400°C and 550°C for 2 h. 100

Beyond 550°C and up to 700°C, a portion of the austenite de-

composed into ferrite and fine carbides.
Reaustenitizing the as-cast structure 1120°C/4 hand
90
• •
quenching with forced air increased the austenite content of 80

..
the matrix from about 76% to 86%. Secondary carbides '#.
a>
were precipitated from the austenite during reaustenitizing <Ill 70
in the range of 900-1035°C; because the austenite was de- 't:
::0
II)
pleted of carbon, a large portion of the austenite transformed 60
!::0
to martensite during quenching to room temperature. At
room temperature, after austenitizing lOOO°C/4 h, the pre- 1>
I!
dominantly martensitic matrix contained about 35% aus- "'- 50
c
tenite, which was reduced to (a) <5% by refrigerating twice 0
<Ill 40
to -78°C, or (b) by heating above 330°C, e.g. to about 25% !
by heating at 550°C/2 h. oct
CD
Hardness and Fracture Toughness. Figure 5 shows the in-
fluence of tempering temperature on K lc and Kid fracture i<Ill
Co)
30

toughness and on the hardness of the austenitic and mar- 20

tensitic structures. Average toughness values are plotted as
data points, and the ranges of test values are indicated by. 10
vertical lines drawn through the data points. The K lc value
of the austenitic iron (Figure 5a) was increased by stress re- 0
lieving 200°C/2 h. A relative minimum in the K lc values oc- w w ~ ~

curred by tempering in the range of 250-400°C (Figure 5a). Volume of Carbides in Metallographic Samples, %
The highest K lc value for a tempered austenitic structure
was obtained by heating at 550°C for 2 h. Heating at tempera· Figure 7. Area of carbides on fracture surface vs. carbide
tures beyond 550°C drastically reduced the K lc values. volume of dynamic fracture toughriess specimens with (a) aus-
Stress relieving the as-cast austenitic specimens 200°C/2 h tenitic structures, as-cast + 200°C/2h and (b) martensltlc struc-
resulted in a large increase in the KId value (Figure 5a). The tures, 900°C/5h, cooled with forced air, refrigerated twice to
highest Kid value was obtained by tempering 330°C/2 h. -78°C, and stress relieved 200°C/2h.
Heating the as-cast austenitic specimens beyond 330°C up
to 700°C produced a significant decrease in KId values.

34 The influence of tempering temperature on the fracture

toughness of martensitic specimens is shown in Figure 5b.
Stress relieving 200°C/2 h caused a large increase in K lc
Kit Stress Relieved
32 900 and Kid fracture toughness and led to the highest values for
all martensitic structures. A relative minimum in fracture
toughness values seemed to result from tempering at 250°C
800
30
and 330°C. The fracture toughness of the as-quenched mar-
tensitic structure, however, was improved by all tempering
~ temperatures used.
28 700 >
:z::
a
The effects of different austenitizing temperatures of
~ 900-1120°C on fracture toughness are shown in Figure 6.
No distinct effect on K lc fracture toughness of as-quenched
<Ill 600 ~
D.. 26
2 <Ill
:z:: specimens was found, but stress relief at 200°C significantly

~ 24
...
....:::
500
increased the K 1c fracture toughness of iron austenitized
at lOOO°C. Kid fracture toughness values, however, showed
Jt
a marked dependence on the austenitizing temperature.
:III: 400
Austenitizing at lOOO°C resulted in the lowest Kid value in
- 22
the as-quenched structures; but when the specimens quench-
'"'"c
CD ed from 950°C to 1120°C were stress relieved at 200°C, the
..c
!' 20
KId values were increased to about the same value. In Figure
~
0 6, the retained austenite values show that the lower aus-
!::0 tenitizing temperatures, 9OO-1000°C, resulted in predomi-
1> 18 nantly martensitic structures; 1120°C, however, resulted in a
I! predominantly austenitic structure.
"'-

16 Fractography
100 '#. Microscopic examination showed that, in both the austeni-
tic and martensitic structures, the amount of carbide on

=1
14
fracture surfaces was substantially larger than the volume of
eutectic and primary carbides measured on metallographic
12 40 ~
CD
specimens. The amount of carbide on the fracture surfaces
20 ·Ii of Kid specimens is shown in Figure 7. At a given carbide
~
oa: volume as determined on polished metallographic specimens,
10
900 1000 1100 the amount of carbides was greater on fracture surfaces of
Austenitizing Temperature, °C specimens with an austenitic matrix. Figure 8 illustrates
Figure 6. Fracture toughness, hardness, and retained austenite the main features produced by cracks propagating in high-
of Heat 63 (2.9C-19.0Cr-2.4Mo-0.9Cu). Specimens were re- Cr / Mo white irons. Cracks propagated through the matrix
austenltlzed at temperatures Indicated and tested as-quenched (Figure 8a)·, along interdendritic carbide networks of irons
or stress relieved 200° C/2h. with a relatively small amount of carbides (Figure 8b), and on
42 JOURNAL OF METALS • October, 1980
 (a) (b) (c)

Figure 8. Fracture surface and fracture toughness specimens: (a) Heat 17A (1.4C-11.6Cr-2.4Mo-1.2Cu) mar1ensltlc struc-
ture containing 7.1% carbides, (b) same heat with an austenitic structure, (c) Heat 20B (3.4C-24.1Cr-2.5Mo-0.9Cu) mar1ensltlc
structure containing 41.1 % carbides.

34
cleavage planes of carbides or at the carbide/ matrix inter-
face in irons with a relatively large amount of carbides 32
(Figure 8c).
IE 30
DISCUSSION '>
Experimental results show how both the volume of mas- ...
0..
~ 28
sive carbides and the structure of the matrix influenced -.::
K lc and Kid fracture toughness values of high-Cr / Mo white u

cast' irons. ::01:: 2,6

:s!
Influence of Carbide Volume ~ 24
Klc fracture toughness values were about equivalent for '"'"CD
c
irons with carbide volumes ranging from 7% to about 20-30%; .c
11/1 22
the values were higher for austenitic matrix microstruc- :::0
0
l-
tures. K lc values decreased rapidly as the carbide content I! 20
increased beyond 30%. Fractographic examination showed :::0
t>
that in heats with an interdendritic carbide network (Heats
16, 17, and 18 particularly) the fracture path tended to ....l! 18
follow the carbide network. The size of the primary austenite
dendrites decreased with increasing carbide volume of the 16
heats. K lc values have been found to increase with a de· AUSTENITIC
crease in the size of the austenitic dendrites 13 similar to the
14
Hall-Petch relation for the influence of grain size on tensile
properties. There was no longer a distinct carbide network 450 500 600 700
in the interdendritic regions at carbide volumes beyond 30%, Hardness, HV50
and the carbides became more massive. With increasing
Figure 9. Relationship between fracture toughness and hard-
carbide volume, fracture along or through the massive car- ness of different microstructures produced by heat treating
bides became the dominating mode of fracture, resulting Heat 63 in a variety of ways.
in a significant decrease in K lc values. While at carbide
volumes below 30% the austenitic matrix had greater K lc
values than the martensitic matrix, the difference in K lc both types of matrix structures, to the decreasing amount of
values of austenitic and martensitic matrices diminished at fracture through the matrix.
larger carbide volumes. A dependence of fracture toughness on carbide volume, V,
In contrast, Kid values were greater for irons with an was empirically found to be approximately:
austenitic matrix than for structures with a martensitic
matrix at the same carbide volume, at all carbide volumes Kid 0: V-1I5 to V-I/4
studied. It is interesting to note that unlike the K lc values for austenitic structures (as-cast + 200°C/2 h),
which, in conformance with general experience, decreased
suddenly with the occurrence of the hexagonal hypereutectic Kid 0: V-liS
carbide, there was a uniform straight-line reduction of Kid for martensitic structures (900°C /5 h - forced air + 2 x at
values with increasing carbide volume in the hypoeutectic -78°C + 200°C/2 h), and
to hypereutectic carbide range investigated. The decrease
in Kid values with increasing carbide volume was due, in K lc 0: V-1I2

JOURNAL OF METALS • October, 1980 43

for both the austenitic and martensitic matrices and for a 5. D.E. Diesburg and K. ROhrig. "Vber die Rissiahigkeit von Chrom-Gu.... isen ...
Giesserei. 63 (1976) p. 25-31.
carbide volume beyond about 20-25%. 6. D. Bums and K.E. Hofer. "Measurement of White Iron Toughness Using an instru-
mented Impact Technique." AFS Transactions. 58 (1977) p. 453-468.
7.I.R Sare. "Abrasion Testing and Fracture Toughness of White Caat Irons." csmo
Influence of Matrix Structure Tribophysics Technical Report 77/ ME. Sept. 1977.
The matrix structure of Heat 63, which had a carbide vol- 8. A.R Johnson. "Fracture Toughness of AlSI M2 and AlSI M7 High-Speed Steels."
Met_ Trans .• 8A (1977) p. 891.
ume of 28%, was varied by different heat treatments (Table 9. G. Berry and M.J. Kadhim Al-Tomachi. "Toughness and Toughness Behavior of Two
II) . Figure 9 shows the K l c and KId fracture toughness of High Speed Steels." Metals Technology. June 1977. p. 289.
10. K.H. Zum Gahr. "Fracture Toughness of Quenched and Tempered Structure. of the
predominantly austenitic and predominantly martensitic Tool Steel 9OMnCrV8." Arch. Eisenhiittenwes .• 49 (1978) p. 581-586.
matrices as a function of bulk hardness of the structures_ . 11. L.R Olsson and H.F. Fischmei.ter. " Fracture Toughness of Powder Metallurgy and
Conventionally Produced High-Speed Steels." Powder Metallurgy. 21 (1) (1978) p. 13-28.
In general, the K lc values of austenitic structures seemed 12. C. Kim. "X-Ray Method of Mea.uring Retained Au.tenite in Heat Treated White Caat
to increase with increasing hardness, while those of marten- Iron.... . ubmitted for publication in J. of Heat Treating, ASM.
13. K.H. Zum Gahr and L.J. Eberhartinger. "The Influence of Grain Diameter on the
sitic structures seemed to decrease with increasing hard- Mechanical Properties of a Precipitation-Hardened Austenitic Steel," Z_ Metallkde, 67
ness. There was no general trend of KId values with hardness (1976) p. 640-645.
of austenitic irons, but KId values generally decreased with
increasing hardness of the martensitic irons_ Figure 9 also
shows that there is only a very poor correlation between hard- ABOUT THE AUTHORS
ness and fracture toughness values_ At the same hardness,
fracture toughness values can differ substantially_
It can also be seen that strain rate, varied to determine
K l c fracture toughness and KId fracture toughness, was Karl-Heinz Zum Gahr graduated with a diplo-
ma in mechanical engineering in 1972 and ob-
another factor that influenced the measured value of frac- tained a PhD in mechanical engineering from
ture toughness of white cast irons. At the very large strain Ruhr-University of Bochum, West Germany, in
rates present in the KId fracture toughness test, the 1975. He was an assistant professor and is
austenitic as-cast and stress relieved (200°C/2 h) structure now senior engineer at the institute Of mater-
had a higher fracture toughness value than stress-relieved ials at Ruhr-University of Bochum. He has
martensitic structures. At the low strain rate used in the been engaged in research on fracture and
K l c fracture toughness test, however, the best stress-relieved crack propagation in metals, and his current
martensitic structure (lOOO°C/4 h +' 200°C/2 h and the research interest is the influence of microstructure of materials
best austenitic structure (as-cast + 550°C/2 h) had com- on abrasive wear. During 1978-79, he was visiting staff metal-
lurgist at Climax Molybdenum Company's Research Laboratory in
parable K lc values. Ann Arbor, Michigan_

William G. Scholz received his BS and MS

References degrees from Wayne State University and
1. J. Dodd and D.J. Dunn, " High Chromium-Molybdenum Alloy Irons for the Mining indus-
the University of Michigan, respectively. In
try," Molybdenum Mosaic, 3 (2) (1978) p. 2-9. 1947 he joined Climax Molybdenum Company,
2. RW. Durman, "Fracture Toughness of a Series of High Chromium Abraaion Resi.tant where he has been a research supervisor
Alloy.," PhD the.is, University of A.ton, Birmingham, Alabama, 1970. since 1961. For the past 10 years, his prin-
3. RW. Durman, Foundry Trade Journal, 134 (1973) p. 645-651.
4. D.E. Die.burg, "Fracture Toughness Test Methods for White Caat Irons Using Compact cipal work has involved the structure and
Specimen.," ASTM STP 559, 1973. properties of cast steels and irons.

Helpful Uterature
(continued from page 37) ~ 98 Gas Scrubber Corrosion: 20-page illus- and sponge iron-based steelmaking, compares
trated brochure offers help in solving corro- increases of EF steelmaking in the u.s. and
sion problems that occur in gas scrubber sys- Japan, and contains a complete listing by com-
~ 93 Vacuum Sintering Furnaces: Brochures tems used to remove 50 2 , pany, plant, location, and capacity of the 47
details the complete line of vacuum sintering AMAX Nickel ferrous scrap and sponge-based steelmaking
furnaces used in such processes as carbide companies in the u.s. Price is $20.00.
sintering and tool steel sintering. Institute for Iron & Steel Studies
GCA/ Vacuum Industries

Hazardous Wastes Regulations: Hazard- ~ 100 NOT Laboratory: Full-service NOT lab-
~ 94 Lubricant Testing Service: Leaflet de- ous Wastes/ RCRA Handbook, a guide to oratory offers a wide range of nondestructive
scribes a lubricant testing service which offers cost-effective compliance with the Re- testing techniques including x-ray and gamma
an economical way of evaluating metalwork- source Conservation . and Recovery Act radiography , magnetic particle, dye and
ing lubricants. (deadline November 19, 1980), provides a fluorescent penetrant, eddy current, ultra-
BNF Metals Technology Centre detailed analysis of the applicable regu- sonic, and visual inspection for the south-
lations, the regulations themselves, sample western u.s.
forms for compliance, and the complete Peabody Testing Services
~ 96 Methanol Carburizing Atmosphere Pro- text of the RCRA statute_ Price is $65 .00.
cess: Effective carburizing atmosphere process Order from Government Institutes, P.O.
that uses high purity nitrogen and methanol to ~ 101 Induction Melting: Bulletin describes
Box 5918, Washington, D.C. 20014; tele-
replace the atmosphere produced by natural induction melting systems that combine flexi-
phone (301) 656-1090.
gas-based endothermic generators is described bility with excellent power density for melt-
in this brochure. ing iron, steel. copper, or aluminum alloys.
Air Products & Chemicals, Inc. Inductotherm Corp.

~ 99 Electric Furnace Steel Production: The

~ 97 Drying System for Particulate Materials: July 1980 IISS Commentary, the second in a ~ 103 Controlled Atmospheres: Brochure on
Technical report describes a patented one-step two-part techno-economic report on electric nitrogen-based neutral hardening discusses the
process for powder blending, granulation, dry- furnace steelmaking, outlines U.s. electric natural gas problem and the nitrogen solu-
ing. and milling. furnace steelmaking growth and its causes to tion for the heat treating industry.
Day Mixing the year 2000, including an analysis of pig iron Aj rco Industrial Gases

44 JOURNAL OF METALS • October, 1980