STP49933S CREEP

V. Kalyanasundaram,1 A. Saxena,2 S. Narasimhachary,1

and B. Dogan3

ASTM Round-Robin on Creep-Fatigueand Creep Behavior of P91 Steel

ABSTRACT: The American Society for Testing and Materials (ASTM),

through its Committee E08 on Fatigue and Fracture subcommittee E08.05 on

Creep-Fatigue Crack Formation, has recently developed a new standard for

creep-fatigue testing (ASTM E2714-09). This paper describes the plans and

preliminary results from a round-robin being presently conducted in support

and verication of this new standard. The choice of the test material (ASTM

Grade P91), the design of the round-robin test matrix, and a machining plan

for the specimens are described. The results of microstructural analysis,

tensile testing, and creep deformation and rupture testing are also presented

along with some preliminary results from creep-fatigue testing. A new analyti-

cal model for representing the creep deformation characteristics of this mate-

rial is also presented and evaluated using the creep data generated as part

of the round-robin program. The results of the round-robin creep-fatigue

testing will be used to make appropriate modications to the test standard.

KEYWORDS: creep-fatigue, crack formation, statistical data analysis, creep

deformation and rupture

Introduction

ASTM E2714-09 [1] covers the determination of mechanical properties pertain-ing to creep-fatigue crack formation in nominally homogeneous materials bythe use of test specimens subjected to uniaxial forces under isothermal

Manuscript received December 22, 2010; accepted for publication March 3, 2011;published online April 2011.1Dept. of Mechanical Engineering, Univ. of Arkansas, Fayetteville, AR 72701.2Dept. of Mechanical Engineering, Univ. of Arkansas, Fayetteville, AR 72701(Corresponding author), e-mail: [email protected], Charlotte, NC 28262.

Cite as: Kalyanasundaram, V., Saxena, A., Narasimhachary, S. and Dogan, B., ASTMRound-Robin on Creep-Fatigue and Creep Behavior of P91 Steel, J. ASTM Intl., Vol. 8,No. 4. doi:10.1520/JAI103712.

Copyright VC 2011 by ASTM International, 100 Barr Harbor Drive, PO Box C700, WestConshohocken, PA 19428-2959.

23

Reprinted from JAI, Vol. 8, No. 4doi:10.1520/JAI103712

Available online at www.astm.org/JAI

Copyright by ASTM Int'l (all rights reserved); Tue Mar 3 15:51:13 EST 2015Downloaded/printed by (INSTITUTO POLITECNICO NACIONAL) pursuant to License Agreement. No further reproductions authorized.

conditions. It concerns creep-fatigue testing at strain rates and/or cycles involv-ing sufciently long hold times to induce creep deformation (and oxidation)during cyclic deformation where cycles to crack formation are affected bycreep.

This test method is applicable to the determination of deformation andcrack formation or nucleation properties as a consequence of either constant-amplitude strain-controlled tests or constant-amplitude force-controlled testswith hold times. It is primarily concerned with the testing of round bar speci-mens subjected to uniaxial loading in either force or strain control, wherein thelatter is recommended. As a result of this round-robin, future improvementsplanned for this standard include, but are not limited to, a more denitive preci-sion and bias statement.

A total of 16 participants from laboratories all over the world are conduct-ing tests under a coordinated set of test conditions. The primary objective of theround-robin is to conduct creep-fatigue tests to characterize the number ofcycles for crack formation while using the procedures specied in the standardto assess variability in the results. The list of participants, their afliation, andthe planned set of tests for each of them is provided in Table 1.

Test Material

The candidate materials considered for the round-robin were from a wide vari-ety of materials that are used in high temperature applications and included gasturbine materials for aircraft and land-based engines, fossil power plants, andnuclear reactor materials. Other considerations included material availability insufcient quantities, offers of sponsorship for material and machining costs,and the interest level in testing the material among the participating volunteers.The test material selected is ASTM Grade P91 steel (donated by the ElectricPower Research Institute (EPRI), Charlotte) that has a creep rupture strengthof 94 MPa at 600C for a life of 105 h. The nominal chemical composition of P91steel in wt% is given in Table 2 [2]. There are two other round-robins with simi-lar objectives that are under way. The Idaho National Laboratory is conductinga separate round-robin on IN617 (a nickel-based superalloy) and the Japan So-ciety for Promotion of Science is conducting one on ASTM Grade P92 material.While these are parallel independent studies, an effort is planned to integratethe ndings from all the studies at a later date.

P91 SteelBrief Overview

Modied tempered martensitic heat resistant steels of type 9Cr-1Mo-Nb-0.2V(P91/T91 as per ASTM A335 [3]/ASTM A213 [4], respectively) developed in theUnited States in the early 1980s, are used in main steam pipes, superheaters,headers, boilers, and turbines in supercritical and ultra-supercritical fossilpower generation plants [5]. As a replacement for low alloy ferritic and austen-itic stainless steels, the high creep strength of P91 permits its use in relativelythinner-wall components. This class of steel also offers the advantages of

24 JAI STP 1539 ON CREEP-FATIGUE INTERACTIONS


TABLE1ListofparticipantsandtestmatrixfortheongoingASTM

round-robin

(Numbersindicatethetotalnumberoftestsplanned

under

those

conditions).

Participants

;P91CrackForm

ation

StrainAmplitude%!

60.25%

60.5%

60.75%

60.5%/10

min

Hold

60.75%/10

min

Hold

60.5%/30

min

Hold

IdahoNationalLaboratory:Laura

Carroll

22

2

EMPASwitzerland:StuartHoldsw

orth

44

TechU.Darm

stadt:AlfredScholz

22

2

CRIE

PI,Japan:Y.Takahashi

22

22

2

GE,Schenectady:David

Knorr

22

2

BAM,Berlin:Hellmuth

Klingelhoeffer

22

2

NASA,Glenn:BradLerch

22

2

ANSTOAustralia:Warw

ickPayton

22

2

Georgia

Tech:RickNeu

22

22

TohokuUniv.:A.T.Yokobori

22

22

NRC,Canada:JonathanTsang

22

2

Univ.ofArkansas:AshokSaxena

Conductcreepdeform

ationandrupture

testingandmetallography

andTEM

ofthetestmaterial

MPAStuttgart:AndreasKlenk/KarlMeile

6

British

Energy:MikeSpindler

22

22

PolitecnicodiMilano:S.Beretta

22

BiSS,India:R.Sunder

22

4

TABLE2Nominalchem

icalcompositionofP91steel(w

t%)2.

SteelGradeP91

CSi

Mn

PS

Ni

Cr

Mo

As

VNb

Al

Cu

NSb,Sn

Fe

0.11

0.31

0.45

0.011

0.009

0.19

8.22

0.94

0.005

0.21

0.07

0.006

0.16

0.039

0.001

Bal.

KALYANASUNDARAM ETAL., doi:10.1520/JAI103712 25


FIG

.1(a)P91pipesectionusedfortheASTM

round-robin

testing;

(b)cross-sectionalview

ofsection2ofthepipesection;(c)

machininglayoutforsubsection2-1

(MaterialcourtesyofEPRI).



low thermal expansion, high thermal conductivity, high corrosion crackingresistance, a low oxidation rate, and good inspectability and weldability [6].These advantages allow this material to be a potential candidate to replace cur-rently used P22 (2-1/4 CrMo) steel and an alternative for future applications inpower plants operating at service conditions greater than 600C and a steampressure of 300 bars.

Test Specimens and Machining Plan

Test specimens were machined from a pipe section 482 mm in outer diame-ter, 1m in length and 47.5 mm in wall thickness [see Fig. 1(a)]. The pipewas renormalized to ensure consistency with the original microstructure,then cut in to three sections along its length and labeled as pipe sections 1,2, and 3, respectively. For this round-robin, the cut section 2 was again cutin to six equal subsections along the cross-section and labeled as shown inFig. 1(b). Specimen blanks were machined from these subsections to accom-modate various specimen sizes and geometries as provided by the partici-pants. Figure 1(c) shows the machining layout for subsection 2-1 as anexample. Specimen sizes and grip congurations were selected by the partic-ipants, but they were required to be within the allowable limits of the stand-ard. Figures 2(a) and 2(b) show two typical specimen geometries and sizesrequested by participants as part of the round-robin for performing creep-fatigue testing and for the supporting creep deformation and rupture testing,respectively.

Microstructural Characterization, Tensile and Creep Behavior

Figure 3(a) shows the microstructure of the renormalized P91 material whereinthe martensite phase can be observed in the lath microstructure arranged inpackets (3040 lm in size) within prior austenite grains that were on average100 lm in diameter. Optical micrographs at high magnications revealed exten-sive carbide precipitates rich in chromium, namely,M23C6, whereM Cr (sizesup to 100 nm), that can be located at grain and packet boundaries and ne car-bonitride precipitation, namely, MX, where M Nb or V and X C and/or N,inside the packets similar to the schematic shown in Fig. 3(b). It has been foundthat this material has excellent creep resistance as its martensitic microstruc-ture includes signicant dislocation content in the lath structure introduced byheat treatment [7].

The University of Arkansas was responsible for conducting tensile (per-formed on-site at Bangalore Integrated System Solutions (BiSS), India) andcreep rupture tests and the subsequent metallographic evaluation of the failedtest coupons. Tensile tests were performed, at room temperature and at thehigh temperature 625C chosen for creep-fatigue testing, on dog-bone speci-mens with a gage length and diameter of 13 and 5 mm, respectively, at an initialstrain rate of 0:002 s1. The tensile properties obtained from these tests are



FIG

.2(a)Creep-fatigu

eand(b)creepspecim

enlayoutusedin

theASTM

round-robin

(alldim

ensionsarein

inches).



FIG

.3(a)OpticalmicrographofP91steelmicrostructure

withtheinsetshowinginclusionsand(b)showsaschem

aticofthe

microstructure9.



listed in Table 3 and were found to be comparable to those published in the lit-erature for P91 steels.

Creep tests were performed on smooth round specimens with a gage lengthand diameter of 25 and 5 mm, respectively, which were designed as per theASTM E139 standard [8] [see Fig. 2(b)]. All tests were carried out at 625C (898 K).Creep tests were carried out under uniaxial static (constant stress and tempera-ture) loading conditions in a lab-controlled atmosphere (2062C and 50 % relativehumidity). The external static load was applied using dead weights and a calibratedLVDT with a repeatability of 0:1 lm was employed to measure elongation duringthe tests. The test temperature was monitored continuously during the entire spanof the tests using two K-type thermocouples wound mechanically at the top andbottom ends of the specimen gage length. The temperature difference between thetop and bottom thermocouples during any test was continuously monitored andfound to be within the allowable limits of62C of the test temperature.

The LarsonMiller parameter PLM is used as a predictive parameter toevaluate the stress level required for a given rupture time [10] and is denotedanalytically as

PLM Tk CLM logtr=1000 (1)

where:Tk test temperature (K),tr creep rupture time (h), andCLM constant (30 for P91 steel).The PLM plotted against the applied engineering stress (external static load

divided by the initial cross-sectional area of the specimen) r in MPa is used toobtain the value of r for a given tr. For this round-robin, the test matrix wasdesigned such that tr ranges from 5000 to 150 h and the corresponding stresslevels range from 102 to 152 MPa (see Fig. 4). The data from the tests conductedas part of this program are plotted with the data from the literature [11] in Fig.4 and were found to lie perfectly within the trends of the literature data, thusonce again conrming that the test material behavior is within the limits of typi-cal P91 steels.

The creep deformation mechanism of P91 steels can be dominated depend-ing on stress and temperature, by cross-slip and dislocation climb > 70MPa,and by grain boundary diffusion < 70MPa [12]. It has been found byothers that for martensitic steels, the metallurgical changes are of vitalimportance as they strongly affect creep resistance properties leading to loss increep rupture strength [13]. From a microstructural perspective, it has been

TABLE 3Tensile test results of P91 steel at room and high temperature (625C).

Test TemperatureC=F

0.2 % Yield Strength(MPa/ksi)

Ultimate Tensile Strength(MPa/ksi)

Elongation(%)

24/75 532.6/77.2 708.4/102.7 26

625/1157 325.1/47.1 343.7/49.8 33



observed that theM23C6 precipitates in P91 link up by rapid directional coarsen-ing during the primary creep regime. The resistance to creep deformation byhindering of dislocation motion is increased by the evolution of this microstruc-ture during the nal stages of primary creep and during the entire secondarycreep regime [14].

Creep strain versus time curves exhibited very short primary ( 10% of tr)creep followed by secondary or steady-state and substantial tertiary creep stagesunder the tested conditions (see Fig. 5). Because of dynamic creep recoverydue to subgrain growth and dislocation migration/annihilation in grainsub-boundaries, the primary creep strain rate starts to decrease until it reachesa plateau at the onset of secondary or steady-state creep. The secondary creepregime represents a dynamic equilibrium between work hardening and creeprecovery processes, wherein a balance between generation of new dislocationsand annihilation of existing dislocations is achieved [15]. The hindrance to dis-location motion due to the evolving precipitates mentioned above must also bepart of the overall dynamic equilibrium during secondary creep stage. The mini-mum creep rate _ess as observed in the secondary creep regime is linearly tusing Nortons power law _ss Arn (where A and n are material constants) andthe power law exponent n and constant A are found to be 8 and9:5 1021, respectively (see Table 4).

The onset of tertiary creep is characterized by accelerating creep rates as aresult of a combination of the following reasons [16]:

(1) increasing stress experienced in localized region(s) of the material dueto necking phenomenon

(2) increasing creep strain accumulation that leads to cavity formation andgrowth and consequent damage that develops in the form of creep cav-ities over time

FIG. 4Larson Miller parameter plot from Ref 11, overlaid with data from the current

round-robin tests at 625C.



FIG

.5Creep

rupture(experim

entalversusmodeled)cu

rves

forthecompletedASTM

round-robin

testsofP91steelat625 C.



(3) microstructural changes that are not associated with the accumulateddamage

The creep rupture ductility for P91 steel is high with the nal longitudinalelongation varying from 1619 %. It can also be observed from Fig. 5 that thecreep strains associated with the primary and the secondary creep regimes arerelatively smaller than those associated with the tertiary creep regime, espe-cially at the higher stress levels. Localized necking occurs at times past 95%of the creep rupture time (i.e., tr) when macro-cracking also appears and con-tributes further to rupture elongation. Similar such observations have beennoted in other studies for this class of steels [9,12,13].

Optical microscopic analysis of ruptured creep specimens showed that thecracking mode during creep rupture is a predominantly transgranular (ductile)fracture with an array of microvoids growing through grains along crystallo-graphic planes towards the nal rupture location [see Fig. 6(a)]. It is possiblethat such a failure mode is due to plastic deformation at high stresses typicallyused in accelerated laboratory testing. It is further noted that these arrays werefound most commonly near material inclusions [precipitates and/or secondaryphases, see Fig. 6(b)].

TABLE 4Steady-state creep rate as a function of stress for P91 test material at 625C.

Applied Stress(MPa)

Steady-State CreepRate h1 Power Law Constants

101.5 0.000 35 n 8:24 A 9:53 1021130.0 0.001 66

136.8 0.003 81

138.3 0.005 23

142.7 0.007 79

151.5 0.007 48

FIG. 6Transgranular (ductile) fracture mode as observed in P91 steel (a) before and

(b) after etching with Nital (3 % nitric acid in methanol) solution (Test condition:

151.5 MPa, 625C).



Creep Deformation Model

In this section, the creep deformation and rupture data are represented usingmathematical equations also known as extrapolation models. Such models areessential for data analysis and structural analysis. Since the creep data pre-sented on P91 clearly exhibit primary, secondary, and tertiary creep behaviors,the focus of this exercise was on choosing a model that is capable of represent-ing the creep behavior in all three regimes and one that also accounts forchanges in deformation kinetics as a function of stress and temperature. Sinceall tests performed were at one temperature, the temperature capability of thechosen model cannot be veried from the current data set. A compilation of theexisting models as applicable to any high temperature material and P91 steel inparticular is provided in Ref [17]. After carefully evaluating all of these models,the authors found that the logarithmic creep strain prediction (LCSP) model tobe most suitable for representing the data on P91steel [18]. This model has theleast number of tting constants and its mathematical form has the naturalshape of a creep curve at constant stress. However, in its current form, thismodel suffers from two shortcomings:

(1) The model does not reduce to the correct form when the boundaryconditions at the start and at the end of any creep test are applied (i.e.,as one asymptotically approaches time t 0 and t tr).

(2) Further, the model does not take full advantage of parameters that canbe measured from the actual tests to reduce the number of ttingconstants.

Hence, a modied LCSP model is proposed here by addressing the aboveshortcomings of the original model (see Eq 2). As per the modied model, atany time t in a creep test beyond 1 h, engineering creep strain et is given as

logt fs logtr blogt b 1

fj 1=p

C (2)

where:

fs blogtr

log1 C

plogru C

p; fj

logru C

p

pr;T p0 p1logr p2=T 273 and b, p0; p1; p2, and C are ttingparameters,

T test temperature C,r applied external stress (MPa),t engineering creep strain at time t,tr time to failure by creep rupture (h),t time to given engineering creep strain (h), ande1; eru et at time t 1 h and uniform strain at rupture, respectively.As noted earlier, typically from 95 % of tr and beyond, macro-cracking starts

to appear because of localized necking and results in an unstable specimen



response thereafter. We also know that the reduction in area varies signicantlybased on the necking characteristics. Hence, the engineering creep strain atrupture (t at time t tr) is taken to be the measured uniform strain at rupture,ru (i.e., strain generated in the specimens gage length before the onset ofnecking in a localized region). This strain can be empirically obtained by evalu-ating the reduction in area Ared in the specimen gage length in regions awayfrom the neck. Rather than using the conventional ductility equation for Ared,an analytical form as shown in Eq 3 is employed in this work. As shown inFig. 7, the diameter of the specimen at locations 1, 2, and 3 is measured andaveraged to obtain dunif and this value is used to compute Aunif:

Ared Aorig Aunif

Aorig(3)

where:Aorig original cross-sectional area in the specimen gage length andAunif uniform cross-sectional area obtained by using dunif (the average of

diameters in regions away from the neck).Minimizing human measurement errors and the effect of complex strain

proles across the specimen gage length were the primary reasons for using theaverage value of dunif rather than using a single diameter value in theunnecked region. The choice of position of locations to compute dunif does not

FIG. 7Pictorial representation to empirically measure the uniform strain at rupture,

eru. Vertical lines numbered 1, 2, and 3 indicate locations where diameter is measuredto compute dunif . Untested specimen in the top is kept as a reference for the creep rup-

tured specimen below.



seem to play a signicant role, as long as they are chosen to be approximatelyequidistant (to capture the diameter variation across the specimen gage lengthof the creep ruptured specimen) away from the neck to the edge of the gagelength markers. Also, it was observed in this work that a choice of three suchlocations is optimal and a larger number of locations does not improve theconsistency in the average value of dunif.

To perform non-linear regression (NLR) of the available creep rupture data,the SOLVERV

R

software routine, available as an additional plug-in in MicrosoftExcel, is employed in this work. A few of the tested creep rupture data wererandomly chosen and few commercial NLR softwares including SOLVERV

R

wereused to non-linearly t this data by minimizing the squares of errors (differencebetween the actual and predicted strain values). It was found that SOLVERV

R

did equally as well, if not better, in all of these cases. Thus, the performance ofthis package as compared with the commercially available NLR softwares wascarefully analyzed and evaluated before its eventual selection. This routinesearches for the set of values of the tting factor constants or parameters thatminimize the sum of squares of residuals, i.e., of differences between eachobservation and the corresponding prediction. From the available test data forP91 steel, the modied LCSP model provided the tting constants as shown inTable 5. As can be seen, the model has relatively fewer tting constants as com-pared to the other models and is consequently more robust [18]. The ttedstrain versus time histories are compared to actual measurements in Fig. 5. Themodel successfully describes the data at various stress levels. Figure 8 demon-strates the tting efciency of the modied LCSP model for P91 steel by com-paring predicted and measured creep rates. Once again, the prediction seems tocorrelate well with the experimental data.

Creep-Fatigue Tests

The creep-fatigue round-robin test matrix has been designed to address preci-sion in the results obtained from tests when utilizing the procedure outlined inthe new standard E2714-09. More specically, the objective is to quantify intra-and inter-laboratory variability in the creep-fatigue data. It is anticipated thatthe standard will be revised as warranted by the results of the round-robin. Forexample, questions such as what percentage drop in the force provides the mostconsistent measure of the number of fatigue cycles for crack formation are

TABLE 5Modied LCSP model tting constants for P91 steel at 625C.

Parameter Value

b 0.27

p0 1.65p1 9.15p2 2553.74

C 6.8



FIG

.8Predictedcreepstrain

ratebymodied

LCSPmodelforP91steelascomparedwiththatofexperim

entalvalues

fortw

odiffer-

enttestconditionsat625 C.



expected to be addressed. As noted earlier, 16 laboratories worldwide areinvolved in conducting the creep-fatigue testing as per the test matrix given inTable 1. The creep-fatigue tests are being conducted at 625C at strain ampli-tudes of 60.25, 60.5, and 60.75 %. The hold times for the tests are 0, 10, and30 min at the peak tensile strain. The strain rate chosen for loading and unload-ing in a triangular wave-form will be 0.025 % per second. The participants areasked to report the number of cycles at various level drops in force starting witha 2 % drop. To determine the creep-fatigue round-robin test conditions, pilottests were conducted by Dr. Stuart Holdsworth of Swiss Federal Laboratoriesfor Materials Science and Technology (EMPA), Switzerland and Dr. YukioTakahashi of Central Research Institute of Electric Power Industry (CRIEPI),Japan and the results of these pilot tests are shown in Fig. 9.

These results demonstrate that the selected test conditions reported inTable 1 meet the criteria for round-robin testing. The test temperaturesand hold times chosen are sufciently high for creep-fatigue interactions to bepresent during the testing.

Summary

In order to further rene the precision and bias statements for the recentlydeveloped ASTM standard E2714-09 for creep-fatigue testing, a round-robinprogram has been initiated on P91 steel with the participation of 16 laboratories

FIG. 9Pilot tests results from creep-fatigue testing of P91 steel, where Na is the num-

ber of cycles to failure. Data courtesy of Dr. Stuart Holdsworth of EMPA, Switzerland

and Dr. Yukio Takahashi of CRIEPI, Japan.



worldwide. The specimen machining, material characterization, and pilot teststudies to nalize test parameters for this round-robin have been completed. Aspart of this round-robin, this paper also reports the results of microstructuralanalysis, tensile and creep deformation, and rupture tests performed thus far onP91 steel. Preliminary microscopic analysis of ruptured creep specimens showsthat material undergoes predominantly transgranular (ductile) fracture with anarray of microvoids found most commonly near precipitates and/or secondaryphases. A modied LCSP model has been successfully developed to accuratelyrepresent the creep deformation characteristics of this material with theavailable data. Some preliminary results from the creep-fatigue tests are alsopresented.

Acknowledgments

The writers would like to acknowledge the technical assistance offered by JeffMincy, University of Arkansas and Jeff Metz, Struers in metallographicspecimen preparation and related work. The data offered by NIRM, EMPA, andCRIEPI (used in Fig. 9) are also highly appreciated.

References

[1] ASTM E2714-09, Standard Test Method for Creep-Fatigue Testing, Annual Bookof ASTM Standards, Vol. 03.01, ASTM International, West Conshohocken, PA.

[2] Parker, J. (P91 material offered by Kent K. Coleman, EPRI) private communica-tion, 2009.

[3] ASTM A33510b, Standard Specication for Seamless Ferritic Alloy-Steel Pipe forHigh-Temperature Service, Annual Book of ASTM Standards, Vol. 01.01, ASTMInternational, West Conshohocken, PA.

[4] ASTM A21310a, Standard Specication for Seamless Ferritic and AusteniticAlloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes, Annual Book of ASTMStandards, Vol. 01.01, ASTM International, West Conshohocken, PA.

[5] Sikka, V. K., Ward, C. T., and Thomas, K. C., Modied 9Cr-1Mo SteelAnImproved Alloy for Steam Generator Application, Ferritic Steels for High-Temperature Applications, A. K. Khare, Ed., Am. Soc. Met, Metals Park, OH, 1983,pp. 6584.

[6] Hald, J., Metallurgy and Creep Properties of New 912 % Cr Steel, Steel Res., Vol.67, 1996, pp. 369374.

[7] Hasegawa, Y., Ohgami, M., and Okamura, Y., Advanced Heat Resistant Steel forPower Generation, R. Viswanathan and J. Nutting, Eds., The University Press, Cam-bridge, United Kingdom, 1999, p. 655.

[8] ASTM E13906, Standard Test Methods for Conducting Creep, Creep-Rupture,and Stress-Rupture Tests of Metallic Materials, Annual Book of ASTM Standards,Vol. 03.01, ASTM International, West Conshohocken, PA.

[9] Fournier, B., Sauzay, M., Barcelo, F., Rauch, E., Renault, A., Cozzika, T., Dupuy, L.,and Pineau, A., Creep-Fatigue Interactions in a 9 Pct Cr-1 Pct Mo Martensitic Steel:Part II. Microstructural Evolutions,Metall. Mater. Trans. A, Vol. 40, 2009, pp. 330341.

[10] Larson, F. R. and Miller, J., A TimeTemperature Relationship for Rupture andCreep Stresses, Trans. ASME, Vol. 74, 1952, pp. 765775.



[11] Gold, M., Tanzosh, J., Swindeman, R. W., Maziasz, P. J., and Santella, M. L., SafeUse Limits for Advanced Ferritic Steels in Ultra-Supercritical Power Boilers,CRADA Final Report No. ORNL00-0598, U.S. Department of Energy, Washington,D.C., 2003, pp. 110.

[12] Gaffard, V., Besson, J., and Gourgues-Lorenzon, A. F., Creep Failure Model of aTempered Martensitic Stainless Steel Integrating Multiple Deformation andDamage Mechanisms, Int. J. Fract., Vol. 133, 2005, pp. 139166.

[13] Sklenicka, V., Kucharova, K., Svoboda, M., Kloc, L., Bursik, J., and Kroupa, A.,Long Term Creep Behavior of 912 % Cr Power Plant Steels,Mater. Charact., Vol.51(1), 2003, pp. 3548.

[14] Spigarelli, S., Cerri, E., Bianchi, P., and Evangelista, E., Interpretation of CreepBehavior of a 9Cr-Mo-Nb-V-N (T91) Steel Using Threshold Stress Concept, Mater.Sci. Technol., Vol. 15, 1999, pp. 14331440.

[15] Orlova, A. and Cadek, J., Dislocation Structure in High Temperature Creep of Met-als and Solid Solution,Mater. Sci. Eng., Vol. 77, 1986, pp. 118.

[16] Annigeri, R., 1997, Life Prediction Methodology for Thermal-Mechanical Fatigueand Elevated Temperature Creep Design, Ph.D. dissertation, Pennsylvania StateUniversity, PA.

[17] Creep-Resistant Steels, F. Abe, T.-U. Kern, and R. Viswanathan, Eds., WoodheadPublishing Ltd., Abington Hall, Cambridge, United Kingdom, 2008, p. 700.

[18] Holmstrom, S., 2010, Engineering Tools for Robust Creep Modeling, Ph.D. dis-sertation, The Aalto University School of Science and Technology, Espoo, Finland.



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STP49933S CREEP