Creep-fatiguebehaviourofanAISIstainlesssteelat550°COriginalResearchArticle

Inthepast,alotofexperimentalstudieshavebeendevotedtocreep-fatigueinteractionsinausteniticstainlesssteels.Testshavebeencarriedmainlyattemperaturesofatleast600°Candathighappliedstrains,whicharesupposedtobethemostdamaging.Thepresentworkisdedicatedtomechanicaltests,TEMobservationsandlifetimepredictionsat550°CwhichcorrespondstotherealindustrialtemperatureinLiquidMetalFastBreederReactors.Itisshownthatifpurefatiguetestresultsareclosetothoseperformedat600°C,someofthecreep-fatigueresultsaredifferent,particularlyforsmallappliedstrainswhichcorrespondoncemoretotheindustrialconditions.Inthe0.25–0.3%strainamplituderange,thestressislargerwithholdtimethanwithoutwhateveristheholdtimeupto5h.Thenumbersofcyclestofailurearegreatlyreducedandnosaturationwiththeholdtimeisobserved,contrarytohighertemperatureresults.Thestress–strainbehaviourisdiscussedconsideringseveralhightemperaturemechanismssuchasageing,recoveryandviscoplasticityandusingTEMobservationsandstresspartitioningintokinematic,isotropicandthermalstresses.Finally,asimplelineardamageaccumulationmodelisappliedtothe550°Cand600°Ctests,usingthemeasuredstresses.Thestressdependenceonholdtimecanpartlyexplaintheobservedfailureresultsonfatiguelife.