The mechanism of acicular ferrite in weld deposits

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1、CurrentOpinioninSolidStateandMaterialsScience8(2004)267–278ThemechanismofacicularferriteinwelddepositsSudarsanamSureshBabu*MetalsandCeramicsDivision,Bldg4508,MailStop6096,OakRidgeNationalLaboratory,OakRidge,TN37831,UnitedStatesAbstractResearchhasshownt

2、hattheacicularferritemicrostructureinsteelweldmetal,whichprovidesanoptimumcombinationofstrengthandtoughness,isindeedintragranularlynucleatedbainite.Itispossibletomaximizethecontentofacicularferritebyincreasingtheintragranularnucleationsiteswhilemaintai

3、ningacriticalweldmetalcoolingrateandthesteelhardenability.Thispaperhighlightsrecentresearchrelatedtonucleationandgrowthofacicularferriteduringdecompositionofaustenite.PublishedbyElsevierLtd.Keywords:Steels;Weldmicrostructure;Acicularferrite;Bainiteandp

4、hasetransformations1.Introductiontemperaturerange1700–1600°C(Fig.1b),solidificationtod-ferrite(bodycenteredcubicphase)startsandenvel-Inthelate1970s,theimportanceofanacicularferriteopstheseoxideinclusions;andthisd-ferritetransformsmicrostructuretowardsop

5、timizingstrengthandtough-toaustenite(c-facecenteredcubicphase).Inthetemper-nesswasidentified[1].Sincethen,extensiveresearchaturerangefrom1600to800°C(Fig.1c),austenitehasbeendoneonacicularferriteformationanditsrela-graingrowthmayoccur.Inthetemperatureran

6、getiontooxideinclusions,weldmetalhardenabilityand800–300°C(Fig.1d–g),theaustenitedecomposestodif-coolingconditions[**2,**3].Anoverviewofthehigh-ferentferrite(bodycenteredcubicphase)morphologies.temperaturephasechangesthatoccurinsteelweldmetalTheausteni

7、tetoferritedecomposition(Fig.1dande)ispresented(seeFig.1)todescribeacicularferritefor-startswiththeformationofallotriomorphicferrite(a)mationinthecontextoftheoverallmicrostructureevo-atpriorc–cboundariesandeventualcoverageoftheselution.Theweldmetalmicr

8、ostructureisaffectedbyboundaries.Withcontinuedcooling(Fig.1f),theWid-melting,gasdissolution,solidificationandsolid-statemansta¨tten(aW)ferritenucleatesatthea/cboundariestransformations.Sincetheweldpoolregionisheatedandextendsintotheuntran