Optimization of the Fatigue Properties

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THE MERIC N SOCIETY OF MECH NIC L ENGINEERS

345 E. 47 St ., New Yo rk, N.Y. 10017

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cussion at meetings of the Society or of its Divisions or Sections, or printed in its publications.

MDiscussion is printed only if the paper is published in an ASME Journal. Papers are available

i

rom ASME for fifteen months after the meeting.

Printed in USA.

91-GT-161

Op tim ization of the F atigue Propert ies

of INCON EL Al loy 617

G. D. SMITH and D. H. YATES

Inco Alloys International Inc.

Huntington WV 25720

ABSTRACT

Rigorous control of the annealing practice and certain

alloying elements can directly influence key characteristics which

aid in optimizing low cycle fatigue (LCF) properties of

INCO NEL O alloy 617. These procedures favorably influence grain

size, carbide microstructure and mechanical prop erties. It is shown

how an optimum combination of these procedures can greatly

improve LCF properties of alloy 617 sheet.

INTRODUCTION

Alloy 617, developed in the early 1970s, is a wrought solid

solution nickel-base sheet alloy intended primarily for high

temperature, high strength applications. The alloy is particularly

used for combustor, transition ducting and exhaust system com-

ponents in aircraft and land-based gas turbine engines. Its use is

predicated on its high temperature strength an d stability, its high

temperature corrosion resistance and, mo st importantly, on its LCF

r e s i s t n c e

The applications for which the alloy were developed

have experienced progressively demanding requirements over the

years since product introduction. Correspondingly, this has

resulted in gradual improvement of alloy 617 to keep pace with

these demands. These property improvements were accomplished

through close customer contact, gradual tightening of

compositional and processing parameters and innovations in

manufacturing capabilities. This paper describes the series of

product and p rocess improvements that have culminated in the

present alloy and its concomitant LCF properties.

CKGROUND

Hicks(') in 1987 reviewed the then current high temper-

ature sheet requirements for gas turbine applications and

compared these performance criteria to a number of sheet alloys

including alloy 617. He found the alloy to possess excellent high

temperature strength of the same order as HAY NESO alloy 188 with

oxidation resistance in high velocity exhaust gas streams superior

to that of alloy 188 and NIMONIC* alloy 86. Thermal stability as

measured by retention of room temperature ductility after expo-

sure at 649C (1200F) for 8000 hours was superior to INCO O alloy

HX and alloy 188. However, at 1050C (1922F) after times to

3000 h ours, room temperature properties of alloy 617 were not

superior to alloy 86, alloy 188, alloy HX and HAYN ESO alloy 230TM .

Hicks attributed the initial property deterioration of alloy 617 to

extensive grain boundary carbide coarsening with associated

dissolution o f matrix carbides. In the latter stage of expo sure, some

additional loss of room temperature properties was attributed to a

tendency of alloy 617 to be susceptible to oxidation fissuring of

surface grain bound aries.

In the mid 1980s, Burke and Beck ( 2

) and Rao, et al (

3

,

examined LCF characteristics of alloy 617. Burke and Beck

obtained LCF data under fully reversed strain conditions at 760C

(1400F) and 871C (1600F) and sought to determine the primary

mechanism of deformation at each temperature. These authors also

reported stress controlled fatigue data at these same tempera-

tures. Rao, et al., examined the influence of time and tempera-

ture dependent processes on strain controlled LCF behavior of

alloy 617. These authors studied the influence of strain rate on

crack initiation and propagation modes at 750C (1382F), 850C

(1562F) and 950C (1742F). More recently, Srivastava and

Klarstrom ( 4

) compared the LCF of production plate of alloy 617

with that of alloy 230TM and HASTEL LOY alloy X (INCO alloy

HX). The above authors examined alloy 617 at constant grain size

as determined by the prior processing history of their sample

material (either as-received or resolution annealed as in the case of

Burke and Beck). Their work was done on sample stock of

OHA YNES and HA STELLO Y are registered trademarks of Haynes International, Inc.

OINC ONE L, INCO and N IMO NIC are registered trademarks of the Inco family of companies.

230TH is a trademark of Haynes International, Inc.

Presented at the International Gas Turbine and Aeroengine Congress and Exposition

Orlando, FL June 3-6, 1991

Copyright 1991 by ASME

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relatively large grain size, i.e., ASTM 3 grain size or larger. The

above authors tested the alloy in the as-received condition except

Burke and Beck who gave their material a solution anneal. The

effect of grain size on the LCF behavior of alloy 617 sheet is the

subject of this paper as is the description of how carbon and

molybdenum w ere increased to enhance grain size control.

EXPERIMENTAL PROCEDURE

The nominal compositions of the alloy 617 heats used in

this study are given in Table I. For comparative purposes, limited

tension-tension, axial stress controlled, low-cycle fatigue testing was

also done on alloy HX and alloy 230TM . The compositions of these

alloys are given in Table I.

Table 1. Composition of The Alloys of This Study (Wt. %)

Alloy

Ni Co

Mo W

Al

Ti

Fe C La

INCONEL alloy 617

XX005UK

Ba l 21.9

1 2 2

8 9

1 4 2

1

0.10

XX0015U K

Ba l

22 .2

1 2 5

9 .0

1 2

3

1 8 0.10

XX0023UK

Ba l 22 .2 1 2 6 9 .1

1 5

3

1 2 0.06

X X 0 0 69 UK

Ba l

22 .0

1 2 5 9 1

1 3

3

2 1 0.06

X XO105UK

Ba l 21 .9

1 2 6

8 9

1 2

0.2

0.9 0.06

X X 0 1 2 0 UK Ba l

21 .8

1 2 5

9 6

1 2 0.2

1 6

0.07

XX0140UK

B al

22 .2 1 2 7 9 8 3

0.3

1 6

0.08

X X 0 1 46UK

B al

21.6 1 2 5 9 6

1 2

2

5 8

X X 0 1 49 UK

B al

22 .0 1 2 5 9 7

1 2

2

1 8

INCO alloy HX

Z0 8 46X G Ba l

21 .4

1 6

9 3

0.2

1 7 8

0.06

Z0 9 77X G

Ba l

21.6

1 7

8 5

0.2

1 8 8 0.07

Z 1 1 5 1 X K

Ba l

21.5 1 5 8 5 0.2

1 9 6 0.07

Haynes Alloy 230TM

Ba l 22 .0

2. 0 1 4 3

0.1 0 0.02

mode, employing a symmetrical triangular strain wave cycle (f = 0.5

Hz). The fatigue testing apparatus was a Model 880 MTS closed

loop servohydraulic system. Test temperatures were achieved using

an electrically heated furnace mounted on the test stand. Axial

strain was measured and controlled by an axial gauge length

extensometer mounted on the test specimen.

. 2 0 1 / . 1 9 9

251 + .

002

Ream

1/2 R..010

.000

Lon

.750 (Re

375

(Ref).020

. 8 5 3

447

400

2.000 .010

3.000 .010

Dimens ions in

Inches

Figure 1. Schematic of.the Axial Strain Controlled

Sheet Specimen (maximum gauge thickness 0.100

.

RESULTS

Because the reproducibility of LCF properties depends on

the consistency of grain size after the final anneal, the effect of the

carbon and molybdenum content of alloy 617 on grain size during

annealing at 1190C (2175F) for various times to 1.5 hours is

examined. The grain size data are shown in Figure 2 for selected

compositions given in Table I.

XX 5UK

Z

Most of the LCF testing (both tension-tension and axial

strain controlled) was done using 4.75 mm (0.187 in.) cold rolled

and annealed [1177C (215 0F)/5 min./WQ] sheet . Grain s ize was

varied, as noted below, by either lowering the annealing

temperature, extending the annealing time or by altering the

composition. The fatigue specimens were taken transversely to

the rolling direction of the sheet. Specimen blanks for the stress

controlled fatigue testing were ground to 170 mm (5.5 in.) x 12.5

mm (0.5 in) x 4.5 mm (0.175 in.) before a central gauge section of

12.5 mm (0.5 in.) x 7.6 mm (0.3 in.) x 4.5 m m (0.175 in.) was machined.

The axial strain controlled LCF specimens were m achined as shown

in Figure 1. Grain size was determined metallographically from a

mount made from the gauge length of each specimen after test-

ing using the phospho ric acid etchant described by M ankins, et al.

.

XX 2 UK

XX 46UK

XX 49UK

XX 4 UK

5

5

UR S

Figure 2. Effect of Composition on Grain Size of alloy

617 Annealed for Varying Times at 1190C (2175F)

The LCF tests were performed in air using both a

tension-tension axial stress control mode [test frequency (f) = 5 0 H z]

and a fully reversed (strain ratio of R = -1) axial strain control

To vary the grain size of a nominal alloy 617, the annealing

conditions and composition were varied as presented in Table II.

Ro om tem perature tensile properties are also given.



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a

E

E

E

E

7

Table II. Effect of Composition and Annealing Conditions on The

Grain Size and Room Temperature Tensile Properties of Alloy 617

Alloy 617

Heat No.

Annealing Condition

Temperature/Time

(min.)

ASTM

G.S.

No.

0.2%

Y.S.

M Pa

0.2%

Y.S.

Ks i

UTS

MPa

UT S

Ks i

El

XX0005UK

1066C 1950F)/5/WQ

9.5 519.2 75.3 1015.6 147.3

35

XX0015UK

2

1177

0C 2150F)/5/WQ

5.0 384.1

55.7

798.4 115.8

53

XX0023UK

1163C 2125F)/5/WQ

2. 5

288.2 41.8 752.2

1 9 1

65

XX0069UK

3

1177 0

C 2150

0

F)/5/WQ

2. 5

339.2 49.2 724.7

1 5 1

64

XX0105UK

;

1163

C 2125F)/5/WQ

4.0

331.0 48 .0 759.8 110.2

61

XX0120UK4

1177C 2150 0

F)/5/WQ

4.5

324.8

47.1

785.3

113.9

56

XX0140UK

1182

0

C 2160F)15/WQ

5.5 377.2 54.7

800.5

1 1 6 1

55

XX0146UK

1182

0

C 2160

0

F)/5/WQ

4.0

368.2

53.4 795.0 1 1 5 3 55

XX0149UK

1182 0

C 2160

0

F)/5/WQ

4.5

388 .8 56.4 810.2

1 1 7 5

53

'High (>0.08%) carbon, high (>9.3%) molybdenum

2

High (>0.08%) carbon, low ( 9.3% ) molybdenum

Figure 3 presents the effect of tension-tension axial stress con-

trolled LCF testing of alloy 617 at 593C (1100F) as a function

of grain size. For comparative purposes, as-received alloy 230TM

(ASTM grain size 5) data are also presented. No attempt was

made to vary the grain size of this alloy. However, the grain size

was varied through control of ann ealing conditions to yield alloy HX

with grain sizes of ASTM # 5, 7 and 10. Their comparative 5 93C

(1100F) LCF results are presented in Figure 4.

1 7

16 0

1000

XXOOOSUK 1065C Annea l ) G.S. = 9.5

1 5 0

1 4

12 0

80 0

1 2

Alloy 230TH Mill Anneal) G.S. = 5.0

11 0

100

60 0 90

0

40 0

G.S. = 4.0

60

50

XX0069UK 1177C Anneal) G. S. = 2.5

40

3

1 0

3

4

0 5

0 6

0 7

CYCLES TO FAILURE

F i g u r e 3 . E f f e c t o f G r a i n S i z e o n t h e T e n s i o n T e n s i o n A x i a l S t r e s s

Controlled LCF Properties of Alloys 617 and 230TM (min. tension

stress = 34.5 MPa; max tension stress as shown).

Test Frequency = 50 H.

14 0

13 0

120 y^

11 0

1

90

8 E

70

60

50

1 0 00

0 2

0 3

0 1

0 5

0 6

CYCLES TO FAILURE

F i g u r e 4 . E f f e c t o f G r a i n S i z e o n t h e T e n s i o n T e n s i o n A x i a l S t r e s s

Controlled LCF Properties of HX (min. tension stress = 34.5 MPa;

max. tension stress as shown). Test Frequency = 50 H

z

Table III presents tension-tension axial stress controlled

LCF data as a function of grain size for alloy 617 at 760C

(1400F). Table IV through VI and Figure 5 present the total strain

controlled mode data for alloy 617 at RT, 760C (1400F) and

871C 1600F).

Table Ill. Effect of Grain Size on The Tension-Tension Axial

Stress Controlled LCF Properties of Alloy 617 at 760C (1400F)

Tension-Tension

Axial Stress

Alloy 617

Heat Number

Annealing Condition

Temperature/Time(min)

ASTM G.S.

Size No.

34.5-413.7 MPa (5-60

ksi) Cycles to Failure

XX0023UK

1163C 2125

F)/5/WQ

2.5

50 0

XX0015UK

2

1163C 212 5 F)/5/WQ

5.0

64.391

XX0005UK3

1163C 2125

0 F)/5/WQ

9.5

93.440

'Low (>0.08%) carbon, low (> 9.3%) molybdenum

2

High (>0.08%) carbon, low (


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Table VI. Alloy 617 Low Cycle Fatigue Data Summary

Heat XX0140UK (ASTM Grain Size 5.5) - 871C (1600F)

Total Strain

Range

Pc t

First Cycle

At

M Pa

Mid Life

At

M Pa

N;

Cycles

Nf

Cycles

N; Nf

Degree of

Hardening

Pe t

1

5 8 2 . 6

6 5 1 . 6 5 2 0 9 6 4

.5 4

1 1 . 8

0 .5

4 6 1 . 3

4 9 7 . 8

2 ,5 9 3 3 ,3 4 8

. 7 7 7 . 9

0.40

4 1 7 . 1 4 3 5 . 8 6 . 7 1 4 8 . 0 0 2 .8 4

4 .5

0 . 2 5

3 2 4 .1 3 2 4 .1

1 3 3 , 3 3 4

1 4 1 , 1 2 6

.9 4

0.0

Tota l Stra in Con tro l led A x ia l Test Con di t ion s: R = 1 . Tes t Freq u ency =

0 . 5

Hz .

2.5

= R .T. Test

=760C

est

A = 871C Test

1.5

ashed lines are cycles

to crack initiation.

Solid lines are cycles to

rupture.

0.5

0

4

CYCLES TO FAILURE

Figure 5. Total Strain Controlled Axial LCF Properties of Alloy

617 at Room Temperature, 760C (1400F) and 871C (1600F).

R

-1. total Frequency = 0.5 H.

DISCUSSION

In alloy 617, carbides serve two practical functions,

strengthen the alloy( and act as an assist to controlling grain

size during annealing.( 2 ) Mankins, et al, (

6

) examined the micro-

structure and phase stability of alloy 617 for times to over 10,000

hours at temperatures from 649 C 1200

F) to 1093C (2000F).

These authors report that the carbide phase present in the alloy

after exposure at all test temperatures was M2006 carbide (where

M is principally chromium plus molybdenum). No M C or M6C

carbides were found and only a very small amount of gamma

prime (less than 1%) w as found to form at 649C (1200F) to 760C

(1400F). Most of the M23C6 carbide present in the alloy is

dissolved in one hour at 1177C (2150F) and, correspondingly, the

grain size is relatively large. Even after 215 hours at 1093C

(2000F) under a creep stress of 7 MPa (1 ksi), relatively little

M23C6 was noted. Their alloy contained 0.07 carbon and 9.0

molybednum. The grain growth characteristics of alloy 617 at these

nominal levels as-annealed at 1190C (2175 F) are given in Figure 2

(alloys XX 0105U K and X X0120U K) and the corresponding LCF

data (tension-tension axial stress controlled mode at 5 93C (1100 F)

are depicted in Figure 3 and also for heat XX 0069U K (ASTM grain

size #2).

Present manufacturing practice establishes a degree of alloy

grain size control for the most commonly specified annealing

temperature of 1177C (2150F) by slightly raising the carbon

content from 0.07% to 0.08% and the molybdenum content from

9.0% to a minimum of 9 .3%. Th is results, when used in conjunction

with a penultimate anneal of 1066C (195 0F), in the formation of 1 to

3% M6 C (where M is principally molybdenum bu t to a lesser extent

chromium) w hich tends to be more resistant to dissolution at

1177C (2150F) than M23C6. The effect of this change on grain

growth at 1190C (2175F) as function of time is given in Figure 2

(a lloy 617 heats XX 0140UK, XX 0146UK and X X0149UK ). The

corresponding ASTM grain size numb er is 4-5 for these heats when

routinely annealed at 1177C (2150F) for 5 min. and effectively

water quenched. The tension-tension axial stress controlled LCF

data at 593C (1100F) for alloy 617 containing 0.08 carbon,

9.3% or more molybdenum, and possessing an ASTM grain size

number of 4, is given in Figure 3. Note its close approach to the

data for alloy 230T

(ASTM grain size number of 5) suggesting

that at equal grain sizes both alloys have similar low cycle fatigue

responses. However, the effect of grain size on the LCF properties

of alloy 230TM was not examined in this paper.

To further investigate the role of grain size on the LCF

properties of alloy 617, heat XX0005UK was annealed for 15

minutes at 1066C (1950F) and water quenched to produce an

ASTM grain size number of 9.5. The tension-tension axial stress

controlled LCF data for this material is presented in Figure 3.

Clearly alloy 617 responds dramatically to changes in grain size.

Not all alloys have such a marked improvement in LCF life as a

function of decreasing grain size. For example, note the small

improvement of LC F properties of alloy HX with decreasing grain

size in Figure 4.

The role of grain size on tension-tension axial stress

controlled LCF at 760C (1400F) for alloy 617 is given in Table

III where fatigue life in cycles is presented as a function of grain

size for a constant tension-tension condition of a maximu m tension

of 413.7 MPa (60ksi) and a minimum stress of 34.5 M Pa (5 ksi).

Again the marked improvement of low cycle fatigue properties with

decreasing grain size is evident. Because commercial product

must balance stress rupture properties (maximized at large grain

size) with LCF characteristics (maximized at small grain size),

ASTM grain size numbers of 4 to 5 are considered the optimum grain

sizes for many of alloy 617's gas turbine applications. Therefore,

using this grain size range, total strain controlled LCF data

were obtained at room temperature, 760C (1400F) and 871C

(1600F). See Tables IV through VI.

Figure 5 depicts the alloy 617 data of Tables IV through VI

for the cycles to first crack initiation (Ni) and the cycles to ultimate

failure (Nf) versus total strain range at the various temperatures

exhibits a very high ratio, on average, of Ni/Nf (only one data point

was less than 50% and the average of all eleven data points was

78.6%). There is a definite tendency for the Ni/Nf ratio to increase

with decreasing total strain range at 760C (1400F) and 871C

(1600F). Overall, the resistance of alloy 617 to crack initiation is

high over the temperature range tested. The degree of hardening

as defined by Equation (1) appears to peak at approximately 35 to

45% at 760C (1400F). This is likely due to work strengthening

associated with the cyclic deformation. At 871C (1600F) and the

lowest total strain range, the degree of hardening is zero suggesting

a balancing of work strengthening and softening reactions.

SUMMAR Y

(a )

The LCF properties of alloy 617 are highly dependent on

grain size.

(b )

The optimum grain size range for both LCF and high

temperature strength p roperties (although not reviewed

in this paper) is considered to be AST M grain size

numbers 4 to 5.

r

S



5/5

(c )

At an ASTM grain size range of 4 to 5, alloy 617, alloy

HX and alloy 230TH have similar LCF properties at

593C (1100F).

(d )

At an ASTM grain size range of 9 to 10, alloy 617

exhibits minimally a two orders-of-magnitude

improvement in LCF properties at both 593C

(1100F) and 760C (1400F ) over the LCF properties

of alloy 617 at an ASTM grain size range of 4 to 5.

(e )

On the basis of eleven data points obtained at room

temperature, 760C (1400F) and 871C (1600F)

under total strain LCF conditions (R = -1), the

average numb er of cycles to crack initiation occurs in

the last quartile of the number of cycles to failure.

(f )

For the temperature and total strain range tested,

alloy 617 exhibited only a modest degree of

hardening, although at the highest temperature and

lowest strain rate the degree of hardening was nil.

The degree of hardening peaks at 760C (1400F) and

high strain rates, where work strengthening may be

occurring.

R F R N S

1 .

icks, B., High Temperature Sheet M aterials for Gas

Turbine Applications, Material Science and

Technology, 3, 1987, No. 9, p. 772-81.

2.

Burke, M. A. and Beck, C. G., The High Temperature

Low Cycle Fatigue of Nickel Base Alloy IN-617, Met.

Trans., 15A, 1984, p. 661-70.

3.

Rao, K. B. S., Schiffers, H., Schuster, H. and Nickel, H.,

Influence of Time and Temperature Dependent

Processes on Strain Controlled Low Cycle Fatigue

Behavior of Alloy 617, M et. Trans., 19A, 1988,

p.359-71.

4.

Srivaetava, S. K. and Klarstrom, D. L., The LCF

Behavior of Several Solid Solution Strengthened Alloys

U sed in Gas Turbine Engines, in Proc. Conf. on Gas

Turbines, Brussels, June 11-14, 1990, American Society

of M echanical Engineers, 90-GT-80.

5 .

Plumb ridge, W. J., D alski, M . E. and Castle, P J., High

Strain Fatigue of A Type 316 Stainless Steel, Fatigue

Eng. Mat. Struct., 3, 1980, p. 177-188.

6.

ankins, W. L., Hosier, J. C. and Bassford, T. H.,

Microstructure and Phase Stability of INCONEL alloy

617, Met. Trans., 5 , 1974, p. 25 79-90.

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Optimization of the Fatigue Properties