连铸机外论文中英文对照资料外文翻译文献.docx

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连铸机外论文中英文对照资料外文翻译文献.docx

连铸机外论文中英文对照资料外文翻译文献

中英文对照资料外文翻译文献

EffectofPorosityonDeformation,Damage,

andFractureofCastSteel

R.A.HARDINandC.BECKERMANN

Acombinedexperimentalandcomputationalstudyisperformedtoinvestigatetheeﬀectof

centerlineshrinkageporosityondeformation,damage,andfractureofcaststeelundertensile

testing.Steelplatescontainingshrinkageporosityarecastinsandmolds,machinedintotest

coupons,andtensiletestedtofracture.Theaveragevolumetricporosityinthegagesectionof

thespecimenswithporosityrangesfrom0.10to0.27pct.Ductilityinthetestcastingswith

porosityismarkedlyreducedwiththepercentelongationdatarangingfrom12.8to19.6pct;vs

22pctelongationforthesoundmaterial.Radiographicimagingisusedtomeasureand

reconstructtheporosityﬁeldinthetestspecimens.Thereconstructedporosityﬁeldisthenused

inaﬁnite-elementstressanalysissimulatingthetensiletesting.Localelasticpropertiesare

reducedaccordingtotheporosityfractionpresent.Porousmetalplasticitytheoryisusedto

modelthedamageduetoporosityandthefracture.Goodagreementisobtainedbetweenthe

measuredandpredictedstress–straincurvesandfracturebehaviors.Thereductioninductilityis

predictedwellbycomparingthemeasuredandthesimulatedelongations.Thecomputational

modelingapproachusedinthisstudyallowsforadetailedevaluationoftheeﬀectofporosity,

includingitssize,shape,andlocation,onthefracturebehaviorofsteelcastings.

DOI:

10.1007/s11661-013-1669-z

TheMinerals,Metals&MaterialsSocietyandASMInternational2013

I.INTRODUCTION

STEELcastingsareunder-utilizedbecauseofuncertaintiesintheirperformanceandlackofexpertiseincastingdesign.Discontinuitiesincastings,likeporosity,playanimportantroleincastingunderutilization.Porositycreatesuncertaintyinadesign’srobustness,sincetherearenomethodologiesforincludingitspresenceinthedesign.Asaresult,designersemployoverlylargesafetyfactorstoensurereliabilityleadingtoheaviercomponentsthannecessary.Contributingtotheissue,theprocessesofdesigningandproducingcastingsareusuallyuncoupledexceptforthespeciﬁcationofnondestructiveevaluation（NDE）requirements.Unlessmdesignengineershavetestdataorexperienceforapart,theycallforNDErequirementswithoutknowinghowthisrelatestopartperformance.Bypredictingporosityaccuratelyfromcastingsimulationandrealisticallymodelingitseﬀectsonthepartperformance,engineerscandeveloprobustdesignsthataretolerantoftheporosityandreliable.Inthecurrentstudy,engineeringapproacheshavebeenappliedtosimulatetheeﬀectofporosityondeformation,damage,andfractureforacaststeelduringtensiletesting,andthesimulation

resultsarecomparedwithmeasurements.ThematerialusedinthisstudyisASTMA216GradeWCBsteel.Itisacastcarbonsteelhavingacombinationofgoodductilityandstrength.Ithasthefollowingchemicalcomposition（maximumwtpct）:

C0.3;Mn1.0;P0.035;S0.035;Si0.6;Cu0.3;Ni0.5;Cr0.5;Mo0.2;andV0.03;andthetotalofCu,Ni,Cr,Mo,andVcannotexceed1.0wtpct.Atroomtemperature,GradeWCBsteelhasayieldstrengthandatensilestrengthof248and485MPa,respectively,and22pctelongationasminimumtensilerequirementsinASTMA216.Failureofsuchductilemetalsoccursonthemicroscopicscalebymechanismsofvoidnucleation,growth,andcoalescence.[1]Voidscanpre-existasmicroporosityandcanalsonucleatefromimperfectionslikesecond-phaseparticles.Afternucleation,voidsgrowwithincreasinghydrostaticstressandlocalplasticstraining.Asvoidsnucleateandgrow,thevoid（orporosity）volumefractionincreases.Thevoidsbegintointeract,andtheporosityfractionatwhichinteractionsbetweenvoidsbeginsisthecriticalporosityvolumefractionfc.Asplasticstraincontinuestoincrease,localneckingandcoalescenceoccurinthematerialbetweenvoidsuntilaconnectedchainofvoidsformsandfailureoccurs.TheporosityfractionatwhichfractureoccursisthefailureporosityvolumefractionfF.Theeﬀectsofporosityonthestructuralperformanceofcarbonandlowalloysteelcastingsonthemacroscopicscalearenotasclearlydeﬁnedastheyareonthemicroscopicscale.Inpreviousstudies,theeﬀectsoflargeamountsofporosityonstiﬀnessandfatiguelifewereinvestigated.[2,3]Porositylessthanafewpercentdoesnotresultinameasurablelossofstiﬀness,orlargestressconcentrations,orstressredistribution,butitgreatlyaﬀectsfatigueresistance.[4,5]Also,thepresenceoflow-levelporositywillreducetheductilityofmetalssincemicrovoidspre-existbeforeanystressisappliedandthenucleationstageisbypassed.Porositylargerthanafewpercentinmetalscausesgrosssectionloss,andlocallyreducestheireﬀectivestiﬀness.[6–8]Thishigher-levelporosityisnotuniformlydistributedthroughouttheentirecastpart,andthematerialpropertiesinthecastingareheterogeneous.Asaresult,stressredistributionoccursinpartsbecauseofmacropores,andstressconcentrationsoccurnearthem,whichleadtolocalizedplasticdeformationandthedevelopmentofmicrocrackscausingfailure.Generallyspeaking,theperformanceofacastingwithmacroporositydependsontheamount,size,andlocationofporosityrelativetothecastcomponent’sgeometryandloading.Allthesefactorsmustbeconsideredtogether.Determiningtheeﬀectsoflargelevelsofporosityonpart,performanceistypicallymorecase-by-casedependentthanforlowerlevelsIthasbeenproposedthatthestiﬀnessandstrengthbehaviorsofporousmaterialscanbecategorizedintothreegroupsbasedonporosityamounts[9]:

lessthan10,10through70pct,andmaterialswithgreaterthan70pct.Thisdivisionispromotedbecausethematerialsattheextremes（<10,and>70pct）behavequitediﬀerently.Thehighestporositygroupisnotapplicabletocaststeels;thesearefoamsandcellularstructures.Theelastic–plasticbehaviorofporousmaterialsinthe10,through70pctporosityrangeexhibitanonlineardependenceontheamountofporosity[2,6–9]Thebehaviorofmaterialsinthelowestrangedemonstrateamorelineardependenceonporosityamount,assumingthatvoidsdonotinteract[10]andbyconsideringisolatedpores,[11]orauniformdistributionofpores.[12]Applyingtheductilefailuremicromechanicalmechanismsdescribedpreviously,onesuchmicromechanics-basedmodelistheporousmetalplasticitymodel.Itisavailableintheﬁniteelementanalysis（FEA）softwareABAQUS.[11–15]Inthemodel,thevolumefractionofporosityisaprimarystatevariable,andtheinelasticﬂowofthematerialismodeledasvoidsgrowandcoalesceathigherstrainsuntilfailureoccurs.Porousmetalplasticitywasdevelopedassumingvoidsaresphericalandgrowasspheres.Italsoassumesthematerial’splasticbehaviorisdependentonhydrostaticpressurebecauseoftheporosity,andthereforeneglectseﬀectsofshearstressesonporousmaterialbehavior.Consideringthisandthelimitationsofporousmetalplasticity,therehavebeennumerousdevelopmentsinmodelingofductilefracture[16]]addressingothervoidgeometriesandstressstates.Whilenotstate-of-the-art,porousmetalplasticityisaconstitutivemodelreadilyavailabletodesignersofcastcomponents,andcanbeausefultooltoinvestigatetheeﬀectofporosityonacasting’sfracturebehavior.Itisacommonconstitutivemodelfoundinmanycommercialﬁniteelementpackages.ThisarticleusestheporousmetalplasticitymodelinFEAtopredicttheductilefractureofcaststeelwithcenterlineporosity.Theprimarygoalofthecurrentstudytestswhetherornotthiscommonlyavailablemodelcanpredictthefractureofsteelwithrelativelylargeamountsofporositydetectablethroughtypicalindustrialradiography.Here,castingswithporositywereproduced,madeintoplatespecimens,andradiographed.Theporositywasquantitativelydeterminedfromtheradiographs.Thecastingsunderwenttensiletesting.Usingporositydatafromtheradiographs,ﬁniteelementstressmodelsofthetestspecimenswithporositywerecreated,andthetensiletestingsimulatedusinganelastic–plasticmaterialmodel.Resultsofthesimulatedfracturearecomparedherewiththemeasuredfracturetotestthemodel’scapabilitiesinpredictingthefracturebehaviorofsteelwithcenterlineshrinkageporosity

II.MATERIALPREPARATION,

MEASUREMENT,ANDANALYSIS

A.CastSpecimensandMechanicalTesting

Forthetensilefracturestudypresentedinthisarticle,WCBsteelspecimenswereproducedfrom2.5cmthick912.7cmwideverticallycastplatesoftwolengths（38.1cmand45.7cm）asshowninFigure1（a）.TheplatesweredesignedthroughcastingsimulationwithMAGMAsoft

[17]tocontaincenterlineshrinkageasshowninFigures1（b）and（c）.Fivecastplateswereproducedandtestedfromthelongerlengthcastings,andfourwereproducedandtestedfortheshorter-lengthcastings.Theletters‘‘D’’and‘‘E’’wereusedtoidentifytheshorterandlongerplates,respectively;followedbynumbers1through5.Thecastplateswerenormalizedandtempered,andmachinedinto19-mm-thicktensiletestcouponswithagagesectionwidthof86mmasshowninthefrontandsideviewsforthespecimeninFigure2（a）.ThetensilespecimendimensionsfortheplateswithcenterlineporosityweredeterminedfromtheASTME8tensileteststandard.[18]Thepositioningoftheextensometeronthenarrow/thicknessfaceofthespecimenisindicatedinFigure2（a）.InFigure2（b）,asmallertensiletestspecimenisshown,whichwasmachinedfromtheporosity-free（or‘‘sound’’）sectionofacastplate.ThespecimenshowninFigure2（b）wastestedtocharacte

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