7/26/2019 Stephens 19Constant and Variable Amplitude Fatigue Behavior84
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R.I.Stephens
J .
H .Chung
A. Fatemi
H.W.Lee
S. G. Lee
C. Vaca-Oleas
C. M. Wang
Materials Engineering Division,
The
University
of
Iowa,
Iowa City, Iowa 52242
Constant
and
Variable Amplitude
Fatigue Behavior
of
Five Cast
Steels atRoom Tem peratureand
- 4 5 C
A comprehensive fatigue program was undertakenat room temperature and
45C (50F for fiverepresentative carbono r low alloycast steels. Constant
amplitude low and high cycle
axial
fatigue behavior,
cyclic stress-strain
behavior,
constant-amplitude fatigue-crack-growth behavior andvariable-amplitudefatigue-
crack-initiation and -growth behavior were determined.
Th e
fatigue resistance at
lowtemperaturewasusuallyequal to or better than at roomtemperatureexcep t for
one m aterial under variable amplitude fatigue crack growth cond itions. SEM
analysis
revealed similar
fatigue crack growth m echanisms at both room and low
temperature, even though some testswere wellbelow the NDT temperature. Most
fatigue resistance for the fivecast steelswasconsistentwith that for wroughtsteels.
Fatigue test procedures
generally
developed with wrough t steels were completely
satisfactory forthese caststeels.
Introduction
Fatigue propertiesof cast steels are not well characterized
relative to wrought steels. Both SAE J1099 [1] and the
Damage
Tolerant Design
Handbook
[2]
contain steel fatigue
properties which are primarily
for
wrought steels
at
room
temperature. Few data exist which describe the effect
of
low
temperature on the fatigue behavior of either wrought or cast
steels. Low temperature fatigue behavior is often considered
to be better than room temperature [3,4]; however, sufficient
information disputes this generalization, particularly for
steels subjected totemperatures somewhat below theirnil
ductility transition (NDT) temperatures
[5,6].
Constant amplitude stress-life, strain-life, and crack growth
rate properties have contributed m uch to the understanding of
fatigue behavior, materials selection, andlife predictions.
However, misconceptions and incorrect design decisions may
be made based upon constant amplitude fatigue behavior
which does
not
provide information
on
sequential and
in
teraction effects with variable loading. A more realistic
comparison of material or component fatigue behavior is thus
determined, not from constant amplitude tests, but from load
or strain histories that closely duplicateor simulate actual
service history and environment.
The goals of this research were to obtain both constant and
variable amplitude fatigue behavior of five representative
carbon
or
low alloy cast steels used
in
the ground vehicle
industries at both room temperature and at a typical low
climatic temperature. The low temperature chosenwas
-45C (-50F) since this
is a
representative low climatic
Contr ibuted by the Materials Division forpubl ica t ion in the
JOUR NAL
O F
E N G I N E E R I N G M A T E R I A L S
AND
T E C H N O L O G Y .
Manuscript received by the
Materials Division, August 3 , 1982.
temperature found inmuch of thepopulated world.The
monotonic, cyclic,
and
fatigue proper ties
or
behavior
ob
tained at thetwo temperatures were: tensile stress-strain,
Charpy
V
notch impact energy, N DT, cyclic stress-strain, low
and high cycle fatigue using smooth axial-loaded specimens in
strain control and in load control, respectively, fatigue crack
growth rates with load ratio (R )set to = 0 and 0.5, and
fatigue crack initiation and growth under two variable am
plitude load histories using a compact type keyhole specimen.
Both macro and micro fractographic analyses contributed
to
an understanding of thefatigue mechanisms at thetem
peratures studied.
Materials Characterization
Ten companies from the ground vehicle industry
cooperated with the Carbon and LowAlloy R esearch
Comm ittee of the Steel Found er's Society of A merica (SFSA)
to help define the five cast steels chosen forthis study.Dif
ferent cast steels rather than different heat treatments of the
same cast steel were chosen to provide more diverse
representative material behavior. The five cast steels chosen
were:
SAE
0030:
normalized and tempered (NT)
SAE 0050A: normalized and tempered (NT)
C-Mn: normalized, quenched and tempered (NQT)
Mn-Mo: normalized, quenched and tempered (NQT)
AISI 8630: normalized, quenched and tempered (NQT)
Their room temperature ultimate tensile strengths and yield
strengths ranged from approximately 500-1150 MPa (72-166
ksi) and300-1000 M Pa (44-143 ksi), respectively. B rinnel
hardness (BHN) varied from 137to305 and both ferritic-
Journal of Engineer ing Mater ia ls and Te chnology JANUARY 1984, Vo l . 106 /25
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pearli t ic and tempered martensitic microstructures were
involved. Thus the five cast steels investigated include a wide
range of representative carbon and low alloy cast steels.
Approximately twenty individual casting blocks were
poured from a single melt for each of the five cast steels. The
cast blocks were heavily risered for proper soundness. The
0030 steel was cast as blocks 115 mm (4.5 in.) x 102 mm (4
in.) x 76 mm (3 in.) while the four other steels were cast as
blocks 470 mm (18.5 in.) long with a trapezoida l cross-section
Table 1 Cast steel heat treatment
0030
0050A
Normalize
Temper
Normalize
Temper
C-Mn
Normalize
r Austenitize
( Water Quench
Temper
30min
90min
4hr
4hr
3hr
lh r
2.5 hr
at
at
at
at
at
at
900C(1650F)
677C(1250F)
900C (1650F)
650C(1200F)
900C(1650F)
900C(1650F)
at 620C(1150F)
Mn-Mo
R epeated twice to obtain complete austenitization.
+
+
8630
Normalize
Austenitize
Water Quench
Temper
3hr
lhr
2.5 hr
at
at
900C(1650F)
900C(1650F)
at 682C(1260F)
Four tempering temperatures between 552C (1025F)
and 682C (1260F) to avoid overtempering.
Normalize
Austenitize
Water Quench
Temper
at
at
900C(1650F)
885C(1625F)
1.5 hr
at 510C(950F)
Table 2 Cast steel chemistryp ercent by weight
C Mn Si S P Cr Ni Mo Al
0030
0050A
C - M n
M n - M o
8630
.24
.49
.23
.34
.30
.71
.93
1.25
1.32
.84
.44
.61
.39
.40
.53
.026
.023
.028
.035
.022
.015
.024
.036
.024
.021
.10
.11
.10
.11
.51
.10
.08
.09
.11
.61
.08
.04
.04
.22
.17
.06
.08
.02
.06
.08
of 140 mm (5.5 in.) high and thickness of 43 mm (1.7 in.) and
69 mm (2.7 in.). The heat treatment and final chemical
comp ositions are given in Tables 1 and 2 , respectively. The
medium carbon 0030 steel and the high carbon 0050A steel
were both normalized and tempered (NT) resulting in a
ferrit ic-pearli t ic microstructure while the low-alloy C-Mn,
Mn-Mo and 8630 steels were normalized, austenitized, water
quenched, and tempered (NQT) resulting in a tempered
martensitic microstructure. The ASTM grain size for both
0030 and 0050A steels was 8 to 9 which is a fine grain size. The
0030 steel had a pproxim ately 75 percent ferrite and 25 percent
pearli te, while the 0050A steel with i ts higher carbon content
had approximately 20 percent ferrite and 80 percent pearli te.
All five cast steels contained the usual inclusions and porosity
as indicated through SEM viewing. The principal inclusions
were MnS; however, other inclusion chemistry was found
using an electron microprobe but these were both much
smaller in size and in number. Hardness tests were made in
three directions on rectangular blocks cut from several cast
blocks for each steel. The hardness variation was not
significant a nd ave rage BH N values are given in Table 3.
Charpy V notch (CVN) impact energy versus temperature,
obtained with standard 10 mm x 10 mm specimens, are
shown in Fig. 1 for the five cast steels. Two vertical lines are
superimposed on the data to indicate the two test tem
peratures relative to the CV N data . The nil-ductil i ty tran sition
(NDT) temperature as determined f rom ASTM standard drop
weight tests [7] are indicated in Fig. 1 by X's . R oom tem
perature is in the CVN upper shelf region for C-Mn and Mn-
Mo steels, upper transition region for 0030 and 8630 steels,
and lower t ransi t ion reg ion for 0050A steel . -4 5 C (- 50 F )
is in the CV N lower tran sitio n or lower shelf region for all five
cast steels. The data for lateral contraction and percent
crystall ine fracture were consistent with respect to energy
values shown in Fig. 1. The NDT temperature is below
- 4 5C ( - 50F ) for C-Mn and M n-M o steels and above that
test tem peratu re for the other three steels.
E xpe r ime nta l Pr oc e dur e s
Equipment.
All tests were perform ed w ith an 80 kN (20
kip) closed-loop electro-hydraulic fatigue test system
equipped with an axially aligned Wood's metal gripping
system for use with axial specimens and a monoball gripping
system for use with CT and keyhole specimens. All low
Table 3 Cast steel average mo noto nic stress-strain properties
^\Property'
Materials^\
0030
0050A
C - M n
M n - M o
8630
0030
0050A
C - M n
Mn-Mo
8630
BHN
137
192
174
206
305
MPa/ksi
496/72
785/114
586/85
703/102
1144/166
544/79
834/121
613/89
758/110
1178/171
.2 S
y
MPa/ksi MPa/ksi MPa/ksi
Ro o m Temperature
303/44
413/60
400/58
544/79
985/143
317/46
434/63
462/67
558/81
999/145
358/52
420/61
434/63
544/79
-
45C(-50*
10* 10
R EVER SALS ,2 Nf
Fig .7
an d
-
Ax ia l fa t igue behav io r
for
8630 cast steel
at
r o om t em pe ra tu re
4 5 C ( - 5 0 F )
curvesareless evident.Nospecific shape comparison is noted
for
the
five cast steels except
at
longer fatigue lives
(> 10
5
reversals), the low temperature strain amplitudesand fatigue
limits
are
between
2 and 25
percent higher than
at
room
temperature. Thusatlonger fatigue lives the fatigue resistance
of
the
smooth axial specimens
at
- 4 5 C
50F)is
better
than thatat room temperature. This increaseis inagreement
with smooth specimen fatigue limits found
by
others
for
wrought steels
[3-6],
At the
shorter lives, mixed results exist
such that
in
some cases
the low
temperature
was
slightly
beneficial, detrimental, or had negligible influence. Low
temperature,
low
cycle fatigue information
is not
generally
available in theliterature; that whichisavailablehasshown
the same trends given
in
Fig. 8 [5,6].The decrease in short life
fatigue resistance at low temperature for C-Mn steel is in
agreement with
the
larger num ber
of
inclusions
and
porosity
found in the low temperature fracture surfaces.
The room
and low
temperature cyclic stress-strain changes
that occurredin the five cast steels, under strain controlled
low cycle fatigue testing compare reasonably with changes
usually foundforwrought steels. Half-life is usually,oroften
considered,
as a
steady-state condition representative
of
stress-strain responseformostofthe total fatigue life; many
exceptions, however, certainly exist [6]. The five cast steels
at
both room temperature and -45C (-50F) completely
satisfy the above wrought steel findings.
For
0030, 0050A and
C-Mn cast steels, half-life values of Aer/2 do represent
majority life steady-state conditions.
For
Mn-Mo
and
8630
steels, continuous cyclic softening existed from start to
fracture. All hysteresis loops showed a dra stic decrease in cr
max
somewhat before final fracture. This dropis due to fatigue
crack growth.
In
many cases,
a
raax
decreased
to
almost zero
before final fracture. Some researchers terminate low cycle
fatigue tests when
a
max
drops twenty percent. These cast steel
tests,
however, were run to fracture. The differenceinlife due
to
a
twenty percent drop
in
a
mm
and
total fracture ranged
10 10 10
s
10*
REVERSALSTOFAILURE,2Nf
Fig . 8
In f luence
of
- 4 5 C ( - 5 0F) tem pe ra t ure
on
axial fat igue
behav i o r
from about 15 to 50percentfor all five cast steelsat both
temperatures. This difference depended upon Ae/2, material
and temperatureand is thesame kindof difference thatcan
occur in w rought steels.
When superimposed, the total strain-life curves
of
Figs.
6-8
tend to band together at short lives (except C-Mn at low
temperature)
and
then tend
to
diverge
at
longer lives.
The
fatigue limits,S
f
,vary from 196to293 MPa (28.5to42.4 ksi)
at room temperature
and
from
241to
365
MPa
(35-53 ksi)
at
-45C (-50F). This range is aboutafactorof 15 forboth
temperatures which
is
somewhat less than
the
factor
of
over
2.0 for therangeofultimate tensile strengths. The 0030 steel
JournalofEngineering Mate rialsandTe chnology
JANUARY 1984, Vo l. 106 /31
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Table 5 Cast steel axial fatigue properties
\Proper ty*
N.
a
f
Material \ MP a/ks i
0030
0050A
C-Mn
Mn-Mo
8630
0030
0050A
C-Mn
Mn-Mo
8630
655/95
1337/194
868/126
1116/162
1936/281
834/121
1282/186
717/104
1096/159
1785/259
e
f
b
c
R oom Temperature
.28
.30
.15
.78
.42
- 4 5
.18
.32
.07
.47
.35
- . 0 8 3
- . 1 2 7
- . 1 0 1
- . 1 0 1
- . 1 2 1
- . 5 5 2
- . 5 6 9
- . 5 1 4
- . 7 2 9
- . 6 9 3
C ( - 5 0 F )
- . 0 8 9
- . 1 1 1
- . 0 6 7
- . 0 9 0
- . 0 9 9
- . 5 0 6
- . 5 8 2
- . 4 3 9
- . 6 7 1
- . 6 5 9
MPa/ks i
196/28.5
237/34.4
248/36
232/33.7
293/42.4
241/35
243/35.2
255/37
269/39
365/53
s
f
/s
u
.40
.30
.42
.33
.26
.44
.29
.42
.35
.31
*See Equa tion for a} ,
ej-,
b, and c
Sf = F atigue Limit
S = U ltimate Tensile Strength
1.4
R=VZ
4
4 0 Room Temp. 1
35 / A
3 0 I f /
J L RO
f / Room Temp.
f^ R = 1/2
'
(-50 F)
-45C S
fR*
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AK-MPay^T
2 0 10 20
R0
9 R.T.
-45C (-50 F)
-e--34C (-30F:
2 0 10 20 10 20 10 20 10
AK -
ksi ^ \r\
Fig. 10 Co nstant ampl i tude fat igue crack growth rate behavior , ~
0
2
- l O
7
?
D
D
5
2
1 0
5
AK-MPa./m
2 0 10 20 10 20
5 0 100
J 1 I I I I, 10
10 20 10 20 10 20 10
AK-ksi ,/irT
Fig.
11 Co nstant ampl i tude fat igue crack growth rate behavior , R
= 0.5
blocks to three criteria are given for each temperature/
history/peak a
no m
/specimen combination. The three criteria
are referred to asN,N
2
, and
N
f
where:
A
7
= numberofapplied blocksto crack initiation defined
as Aa
=
0.25 mm 0.01in.)
N
2
= number of applied blocks to Aa=2.5 mm 0.1in.)
N
f
= numberofapplied blocks to final fracture
The average numberofblocksforeach test condition are also
included in Ta ble 6.
A typical S-N type log-log plotofpeaka
nom
versus num ber
of applied blocks to the three criteria as taken from T able 6 is
shown
in
Fig.
12 for
C-Mn cast steel. The solid data points
and solid curvesare for the
T/H
history and theopen data
points and dashed curves are for the modT /H
history.
Circles
represent
N
t
squares represent
N
2
and triangles represent
blocksto final fractureN
f
. All curves showninFig. 12 have
been drawn as straight lines through the approximate average
of the datafor agiven life criteria. This was doneas an ap
proximation nottoclaimapower law relationship, buttoaid
in viewing the overall test results.
Jou rnal of Enginee ring M aterialsandTe chnology
JANUARY 1984,Vol.106/33
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Table 6 T /H and mod T /H Blocks to three crack length criteria
Material
0030
Peak
Nominal
Stress
ff
nom
M P a (ksi)
393
(57)
314
(45)
275
(40)
Task
1
2
3
Ave.
1
2
3
Ave.
1
2
3
Ave.
Ro o m Temperature
T /H History
N,
40
18
16
25
79
67
35
60
124
80
52
85
Blocks
M
65
39
27
44
102
77
78
86
156
134
130
140
N
f
97
54
54
68
169
141
130
147
313
270
213
265
m o d T /H History
AT,
180'
247
113
180
373
322
347
Blocks
N
2
273
355
193
274
522
388
298
403
N
f
346
453
340
380
751
567
477
588
L o w Temperature
T /H
History
N,
51
37
44
89
130
110
149
155
153
Blocks
N
2
91
63
77
163
186
170
185
187
186
N
f
149
96
123
254
304
279
351
364
357
*
m o d T /H History
N,
200
367
283
639
517
578
Blocks
M
283
462
372
716
637
676
N
f
431
674
555
968
925
946
0050A
C-Mn
Mn-Mo
8630
393
(57)
314
(45)
275
(40)
1
2
Ave.
13
28
21
58
76
67
113
125
119
109
123
116
224
190
207
307
286
296
73
89
81
91
97
94
98
99
99
218
194
206
346
200
273
1
2
Ave.
250
258
254
338
340
339
532
597
564
1310
615
912
1412
736
1074
1718
1159
1439
696
390
543
741
438
590
946
705
825
2262
2262
2393
2393
1
2
Ave.
495
696
595
746
1020
883
1283
1497
1390
760 1260
760
1260
1940
1940
347
211
279
314
(45)
1
2
Ave.
103
100
101
155
236
296
297
399
348
424
339
382
595
605
600
760
873
816
55
100
78
130
168
149
212
271
242
620
731
675
676
803
740
722
897
810
275
(40)
393
(57)
1
2
Ave.
1
2
Ave.
233
212
222
31
31
31
433
235
334
54
63
59
656
445
550
108
114
111
175
100
137
235
224
230
331
328
330
265
214
239
30
32
31
303
250
277
80
82
81
379
419
399
169
179
174
221
229
224
302
326
314
492
449
470
314
(45)
1
2
Ave.
105
92
98
141
147
143
285
288
286
430
395
412
491
530
510
641
798
720
139
91
115
287
190
238
606
640
633
735
1105
920
783
1270
1026
1011
1583
1297
275
(40)
393
(57)
1
2
Ave.
1
2
Ave.
78
100
89
38
28
33
259
205
232
116
86
101
606
668
637
262
224
243
170
174
172
263
341
302
409
526
468
158
167
162
19
91
55
361
315
338
108
146
127
746
751
748
259
292
275
278
306
292
423
355
389
_
615
523
569
314
(45)
1
2
Ave.
100
209
154
197
295
246
635
551
593
429
501
465
762
646
703
1103
957
1030
306
252
279
368
350
359
629
629
661
1346
1003
730
1406
1068
1056
1713
1385
275
(40)
393
(57)
1
2
Ave.
1
2
Ave.
287
243
265
125
116
120
482
398
440
170
185
177
795
758
777
308
352
330
420
490
455
482
566
524
648
709
678
224
224
110
217
163
793
793
221
253
237
1313
1313
394
360
377
616
620
618
640
690
665
739
874
806
2746
2746
-34C (-30F) for 0030, -45C (-50F) for others
From Table 6 and Fig. 12, very little scatter for the three life
criteria existed in the duplicate tests (triplicate for 0030 at
room temperature) for all five cast steels. Scatter of life to
fracture was between a factor of 1and 2 . Most of this scatter,
however, was less than a factor of 1.5. Greater scatter ranging
from a factor of
1
to abou t 4 occurred for crack init iation, Aa
= 0.25 m m (0.01 in.), which can be attributed to the as-dril led
keyhole notch surface roughness variation, multiple interior
cracks, and the exact decision as to when a surface crack was
visible. Most of the scatter for crack init iation, however, was
less than a factor of 2. Macro fatigue cracks grew essentially
perpendicular to the applied load in almost all cases and a
general deviation from this plane was usually within five
degrees. For a given test specimen, only one predominant
surface crack grew past Aa ~ 2.5 mm (0.1 in.); however, as
many as 1 to 4 surface cracks init iated from the keyhole
notch. These multiple small cracks either became non-
propagating cracks or coalesced with the predominant crack.
The number of blocks within the three l ife criteria regions
given in Table 6 for a given specimen and test condition
rang ed from 15 to 75 perce nt of total life for crack initia tion,
5 to 50 percent to grow the crack to Aa = 2.5 mm (0.1 in.),
and followed by 20 to 70 percent to grow the crack to frac
ture. Thus all three regions, in general , significantly con
tributed to the total life of the five cast steels. This implies the
importance of considering both crack init iation, growth of
short cracks from notches, and growth of longer cracks in a
total fatigue life prediction procedure.
The magnitude of the peak a
nom
had the greatest influence
on all three life criteria. Following this influence was the
effect of removing the compression from the block history.
The mod T /H data in Table 6 and the dashed lines and open
34 / Vo l . 106, JANU ARY 1984
T ransac t i ons o f the ASME
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APPLIED BLOCKS
(a) Room Temperature
Aa * 0.25mm 0. 01 in}
Ao ' Z.5
mm 0.1
In)
fracture
APPLIED BLOCKS
(b) ( -30 -F ) -45 C
Fig.12 Peak
7/26/2019 Stephens 19Constant and Variable Amplitude Fatigue Behavior84
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e 863
Fig. 3 SEM fractographs from fatigue crack growth regions at room
and
low
temperatures
the fact
of
its higher crack growth rates at the low tem
perature. The growth mechanism appears to be similar to that
operating under constant fatigue crack growth conditions,
i.e., a ductile type transcrystalline mechanism. Thus, under
both constant and variable amplitude loadings, fatigue crack
growth mechanisms at temperatures both above and below
NDT values were similar. The NDT temperature value
for
OOSOA was 27
c
C 80F which is well above the 4SoC
- SdOF test temperature.
Relative Material Ranking
The selection or comparison of materials based upon
fatigue resistance is an important engineering decision. A
summary and ranking
of
different measures of fatigue
resistance at room temperature for the five cast steels is given
in Table
7.
The numbers in the parentheses refer to the
ranking of the five cast steels for each measure of fatigue
resistance. Ranking 1 is the best and ranking S is the lowest. A
difference factor is also provided in Table 7 which was
calculated by dividing the highest value by the lowest value for
a given criteria. In many cases, the difference factor
is
quite
small, indicating reasonable similarity between the five cast
steels for a particular test condition. The axial fatigue values
were obtained from
data
in Table S and from t 2N
f
curves
such as Figs. 6 to
8.
Constant amplitude fatigue crack growth
rates were taken as median values from Fig. 10. The variable
amplitude values include comparisons based upon fatigue
crack initiation life,
j
, crack growth life N
f
-
j
and total
fatigue life,
f
These values were obtained by summing the
average number
of
blocks for each value
of
peak
U
nom
given in
Table 6 for both the T and mode T histories.
From Table 7, it
is
evident that no one material was always
ranked first
or
last. The ranking
of
the fatigue limit,
Sf
seems
to best agree with the ranking f rom the three variable Jm-
pli tude cri teria. Here 8630 and 0030 consistently have the
higher and lower fatigue resistance, respectively. The constant
amplitude fatigue crack growth properties have the greatest
similarities and it is difficult here to provide a 1 to S ranking.
The low cycle fatigue ranking
at
10
3
reversals has the greatest
disagreement with the variable amplitude results. Since the
variable amplitude
T
and mod
T
loadings with the
keyhole notch specimens most closely simulate real-world
conditions, it appears that
final room temperature fatigue
resistance rankings based on these rankings should be: 8630,
Mn-Mo, C-Mn
or
OOSOA and then 0030. Thus, as indicated
previously, constant amplitude fatigue properties may not be
indicative of variable amplitude behavior.
At low temperatures , many rankings were similar to the
room temperature rankings. The most noticeable discrepency,
however, was that fatigue crack growth resistance of OOSOA
with the variable amplitude loading was quite poor; however,
the constant amplitude tests showed equal or greater fatigue
resistance than at room temperature. Thus, the OOSOA steel
was not recommended for this low temperature service, yet
the constant amplitude tests did not suggest this deleterious
fatigue crack growth resistance.
- 50
0
F _45
0
c
30
0
F _34
0
c
- 50
0
F -4 5
0
c
_50
0
F -4 5
0
C
- 50
0
F -45
0
C
c C-Mn
a 3
d Mn-Mo
R.T.
R T
R.T.
R.T.
R.T.
measuring the striations due to various orientations, banding
randomness and the too often ill-defined str iations. The
str iation spacings turned out to be essential ly statist ically
constant at all crack lengths and hence independent of stress
intensity factor range. Thus a realistic comparison of crack
extension per cycle could not be correlated with striations.
Variable Amplitude Tests. The SEM fractographic
analysis of variable amplitude test specimens indicated few
str iations but showed that transcrystall ine ducti le fatigue
crack growth mechanisms were operating for both room and
low temperatures. This was also evident in OOSOA steel despite
Conclusions
1. The material properties obtained in this research should
be considered as representative values for these five classes of
cast steel. Differences in heat to heat and pouring procedures
and lesser control on microstructure could, however, result in
significant changes in material properties.
2. The fatigue test procedures developed principally with
wrought materials are equally applicable to carbon and low
alloy cast steels.
3. Values of low cycle fatigue materia l propert ies and
cyclic stress-s train properties for the five cast steels were
36 /
Vol. 106, JANUARY 1984
Transactions
of
the ASME
wnloaded From: http://materialstechnology.asmedigitalcollection.asme.org/ on 01/28/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use
7/26/2019 Stephens 19Constant and Variable Amplitude Fatigue Behavior84
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Table 7 Summ ary of average room temperature properties and relative rankings
Dif f e r e nc e
M a t e r i a l P r o p e r t y 0 0 3 0 0 0 5 0 A C - M n M n - M o 8 6 3 0 F a c t o r
C o n s t a n t A m p l i t u d e U n n o t c h e d A x i a l F a t i g u e
e
fl
a t 10* r e ve r sa l s . 009 4 ( 1 ) . 0086 ( 2 ) . 006 4 ( 5 ) 70078 ( 3 ) . 0076 ( 3 )
L5
S y a t l O
7
r e v e r s a ls M p a / k s i 1 9 6 / 2 8 ( 5 ) . 2 3 7 / 3 4 ( 3 ) 2 4 8 / 3 6 ( 2 ) 2 3 2 / 3 4 ( 3 ) 2 9 3 / 4 2 ( 1 ) 1 .5
C o n s t a n t A m p l i t u d e cla/dN
da/dN&t AK = 1 5 M P a v m
fo r R 0 ( m / cy c l e) 3 x l 0 ~
9
( l ) 7 x l 0 ~
9
( 2 ) 7 x l 0 ~
9
( 2 ) 8 x 1 0 " ' ( 2 ) 8 x l 0 "
9
( 2 ) 2 .7
da/dN at AK = 5 0 M P a V r n
f o r = 0 ( m / c y c l e ) 8 x l 0 ~
7
( 4 ) 9 x l 0 ~
7
( 4 ) 5 x l O "
7
( l ) 6 x l 0 ~
7
( 3 ) 4 x l 0 ~
7
( l ) 2. 3
V a r i a b l e A m p l i t u d e
C r a c k i n i t ia t i o n 7 7 / / a n d m o d T/H
E b l o c k s t o / V , 7 1 1 ( 5 ) 8 4 1 ( 3 ) 7 6 8 ( 4 ) 1 0 8 9 ( 2 ) 2 3 8 7 ( 1 ) 3 . 4
C r a c k g r o w t h T /H a n d m o d T/H
b l o c k s o fN-N 7 3 7 ( 5 ) 1 2 8 9 ( 3 ) 1 2 6 5 ( 3 ) 2 4 9 1 ( 1 ) 2 0 1 4 ( 2 ) 3 . 4
To ta l l i f e T /H a n d m o d T/H
I,ioN
1 4 4 8 ( 5 ) 2 1 2 0 ( 3 ) 2 0 3 3 ( 3 ) 3 5 7 0 ( 3 ) 4 3 9 1 ( 1 ) 3 . 0
( va lue s in pa r e n the s e s a r e r e l a t i ve r a nk i ngs ) 1 = be s t r e s i s t a n c e , 5 = l owe s t r e s i s t a nc e
within the ranges found in SAE report J1099 for wrought
steels. Cyclic strain softening and hardening in these five cast
steels was also similar to that found in wrought steels.
Constant amplitude fatigue crack growth behavior was
equivalent to, or beter than wrought steels.
4.
Fat igue resis tance at -45C (-50F) was essen t ial ly
equal to or better than at room temperature except for 0050A
crack growth under variable amplitude loading. The NDT
temperature thus appears to be a conservative criterion for
establishing lower temperature bounds for adequate fatigue
resistance. The NDT temperature does not indicate a possible
ductile/brit t le transition of fatigue crack growth mechanisms
in these five cast steels.
5.
R anking of these five cast steels based upon constan t
amplitude tests did not necessarily agree with rankings based
upon variable amplitude loading. This indicates the im
portance of selecting the proper load spectrum for simulated
and field testing.
A c k n o w l e d g m e n t
The authors would like to thank the Steel Founders' Society
of Am erica, The U niversity of Iowa, and c ontributing
companies for financial sponsorship of this research.
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JANUARY 1984, Vo l. 106/37