1.IntrodctionStainlesssteelsplayanimportantpartinmodernlivingsincetheyhavegoodcorrosionresistanceandapleasingappearance.Thereareseveraltypesofstainlesssteel(typi-calcompositionsaregiveninTable1):3seriescontainCrandNiandusuallycontainMotheyhaveametastableausteniticstructure4seriescontainCr(butnoNisincethisstabilisestheaustenite)andhaveaferriticstructurebutmartensiticphasescanbeedinsomecases(e.g.410)whenoil-quenchedorair-cooled6-seriesareprecipitation-hardenedalloysandtendtocontainCrandNiinloweramountsMathematicalmodellinghasbecomeanestablishedtoolforimprovingprocesscontrolandproductquality.How-everithasbeenshownthataccuratethermophysicalprop-ertydataareneededforreliablepredictionsofdefects1)orimprovedproductquality(e.g.WeldprofilesinTIGGTAwelding23).Thisstudyseekstoprovidereliablethermo-physicalpropertydataforalltypesofstainlesssteels.Theprincipalobjectiveofthisworkwastoestablishequationswhichprovidereliabluesforthermo-physicalpropertiesforthefullrangeofstainlesssteels.Thegeneralapproachadoptedheremakesuseoffactthatthethermo-physicalpropertiesofFeCrandNiareverysimilarthusdifferencesinNi%andCr%indifferentstainlesssteelsdonothaveasignificanteffectonthepropertyvalue.Itshouldbenotedthatferriticandmartensitic(i.e.4-se-riesalloys)undergoamagnetictransitionandsubsequentlytranstoaustenite.Thuesofpropertiessuchasdensityandenthalpyarelittleaffectedbythesetransitionsbuttheirtemperaturecoefficientsi.e.heatcapacity(Cp)andthermalexpansioncoefficient(a)respectivelyalongwiththethermaldiffusivitydovaryappreciably.Con-sequentlyinthesecasesitisnotalwayspossibletogiveoneequationtocoverallthepropertiesforalltypesofstainlesssteel.Thermalandelectricalconductivity(orresistivity)valuesareaffectedbythemicrostructureofthesolidsamplewhichisinturndependentupontheheattreatmentandthecoldworkgiventothealloy.Inthesecasesthethermalconduc-tivityandelectricalresistivityrefertosampleswiththemaximumconductivityorminimumresistance.PropertyvaluesbasedonthevariousrecommendedequationsaregivenattheendofthepaperinTables3and4.TheliquidustemperaturesTliqofthevarioustypesofstainlesssteelswereestimatedusingthecoefficientsrecom-mendedbyHowe.4)ThecalculatedvaluesareshowninTable1.IthasbeenassumedinTable3thatliquidustem-peratureof3-and6-seriesalloysoccursat1723Kandfor4-seriesalloysat1773K.2.Density(rr)ThermalExpansionCoefficient(aa)2.1.DatabaseThermalexpansiondatahavebeenreportedbyBogaardetal.5)foraustenitic304steelandferritic430stainlessISIJInternationalVol.44(2004)No.10pp.1661166816612004ISIJEquationsfortheCalculationoftheThermo-physicalPropertiesofStainlessSteelKennethC.MILLSYuchuSUZushuLIandRobertF.BROOKS1)DepartmentofMaterialsImperialCollegeLondonSW72BPUK.E-mail:kenmillsyuchu.suimperial.ac.ukz.liimperial.ac.uk1)NationalPhysicalLaboratoryTeddingtonTW11OLWUK.E-mail:Rob.Brooksnpl.co.uk(ReceivedonMay62004acceptedinfinalonJuly82004)Equationshavebeenderivedtocalculatuesofthethermophysicalpropertiesofallstainlesssteelsfortemperaturesbetween300and1800K(austenitic3seriesferritic-4seriesandprecipitation-hardened6-se-riesalloys).Valuesofthefollowingpropertiesaregiveninbothfiguresandtables:density(r)thermalex-pansioncoefficient(a)heatcapacity(Cp)enthalpy(HTH298)thermalconductivity(l)andthermaldiffusivi-ty(a)electricalresistivity(R)viscosity(h)andsurfacetension(g).KEYWORDS:stainlesssteelsthermo-physicalpropertiesdensitysurfacetensionviscosityheatcapaci-tyenthalpythermalandelectricalconductivity.Table1.Typicalchemicalcompositions(inmass%)ofexam-plesof3-4-seriesand6-seriesstainlesssteelsandcalculatedliquidustemperatures.steels.Densitydataforsolid304316410and446stain-lesssteelsarecitedbyTouloukian6)andbyMills7)for304and316.Densitydatafortheliquid316alloyhavebeenre-portedbyMcCormickandBrooks8)andfor430byLietal.9)Experimentaluncertaintieseasurementsareproba-bly2%fordensity(r)and10%forthelinearthermalexpansioncoefficient(a).2.2.AnalysisofDataThermalExpansionCoefficient(a)Bogaardetal.5)reportdatawhichgivesthefollowingequationforaustenitic304steel:a(K1)15.80.6102(T298).(1)AscanbeseenfromFig.1attemperaturesbelow1000Ktheferriticphase(in430)hasalowerathanthatforaustenite(in304)above1000Ktheausteniteedresultsinahigheravalue.5)ThusthethermalexpansionforferriticalloyscanbecalculatedusingEqs.(2)and(3).T(2981000K)a(K1)10.20.6102(T298K).(2)T(10001700K)a(K1)14.22.4102(T1000K).(3)Densities(r)Densitieswerefirstcalculatedbyassumingthatthefol-lowingequationapplied:.(4)wherexmolefractionandthat123etc.refertodifferentmetalliccomponents.InactualfactthisrelationismorecorrectwhenusingthemolarvolumeVthanfordensityrbuttheerrorsassociatedwiththeaboveassumptionaresmall.Numericalanalysisoftheexperimentaldensitydatagavethefollowingequations:Solid:rT(79.6%Fe)(78.3%Cr)(85.4%Ni)(76.9%Mn)(60.2%Mo)(47.1%Si)0.5(T298K).(5)Liquid:rT(69.4%Fe)(66.3%Cr)(71.4%Ni)(57.2%Mn)(51.5%Mo)(49.3%Si)0.86(T1823K).(6)Equation(5)makesuseofanaveragueforamoreexactvaluescanbeobtainedby