Stephens 19Constant and Variable Amplitude Fatigue Behavior84

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*


9/13

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



10/13

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



11/13

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


12/13

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



13/13

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.

References

1 "Technica l R epor t on Fa t igue Proper t ie s , " SAE J1099, Soc ie ty of

Automative Engineers , Feb. 1975 ,SAE Handbook.

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MCIC-H B-01, Meta ls and

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5 S tephens , R . I . , Chung, J . H. , and Glinka , G. , " Low Tempera ture

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12 Landgraf, R . W. , "Th e R esistance of Meta ls to Cyc l ic Deformation , " in

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ASTM STP 467,

1970, p. 3.

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Society of Ame rica, R esearch Rep ort 94A, Oct. 1982.

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Mechanisms,

ASTM STP 675 ,1979, p . 292.

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JANUARY 1984, Vo l. 106/37

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