281-paper-influence of heat treatment process on m

联系人：李朝锋，26647182InfluenceofHeatTreatmentProcessonMechanicalPropertiesofanHSLA-100steelLIChaofeng1ZHANGYongjiaMAZhaohui(1.ResearchInstituteforAdvancedStructuralSteel,R&DCenter,BAOSTEELShangHai201900,China)Abstracts：TheprocessparametersincludingthereheatingquenchinganddirectquenchingforthehighstrengthandhightoughnessHSLA-100steelplateswereexamined,andthebestcombinationofstrengthandhightoughnesswereobtained.Agehardenableofcopperparticlescanenhancethestrengthwasthesignificantfeatureofthesteel.Theyieldstrengthwereimprovedwiththedirectquenchingprocessandalsohightoughnessatlowtemperaturewereobtained,itprovedthatreheatingquenchingprocesscanbereplacedwithdirectquenchingprocess.Basedonthestudyofheattreatment,anewshipbuildingsteelplatewithminimumyieldsstrength690MPa,CVNat-85℃wasabove200Jandwithexcellentweldabilityweredeveloped.Keywords：HSLA-100,directquenching,copperagehardenable,shipbuildingplate0Introductions:CopperagehardenableHSLA-100steelhadbeenwidelyusedintheUSAnavyshipbuilding;itwasanothercopperagehardenablesteelwhichwasdevelopedinordertoenhancetheyieldstrengthbasedonthesuccessfulstudyontheHSLA-80steel.Thebehaviorofthecopperprecipitationhadbeenstudiedbyvariouscountries,themaincharacteristicofthesteelwascopperprecipitationtoenhancethestrengthtomakeupforthelostofcarbon[1-5].Inordertoenhancethestrengthandtoughness,Ni、Cr、MowereaddedtocontroltheMicrostructurechangedfromferriteandpearlitetomartensiteandbainite.Thecompositionsofthesteelhadlowcarboncontentsabout0.06%toimprovetheweldablilityofthesteel.TheconditionofdeliveryoftheHSLA-100steelwasquenchedandtempered.Withthedevelopmentoftherollingequipmentandthecontrolrollingandcontrolcoolingtechnology,theon-linedirectquenchingprocess(DQ)wasappliedtoenhancethestrengthandthetoughnessofthesteel,anditwascometruetoreplacetheconventionaloff-linereheatingquenching(RQ)processbytheDQprocess.ThegrainswererefinedwiththeacceleratecoolingandthestrengthandtoughnesswerehigherthantheRQTwithhigherhardenability,simultaneouslytoreducethecostoftheproducts.ThispaperwasmainlyconcernedwiththeDQprocesswiththeHSLA-100steel,theexperimentoftheRQprocesscomparedwiththeDQprocesswerecarriedout.1LichaofengResearchInstituteforAdvancedStructuralSteel,R&DCenter,BAOSTEEL,021-26647182Email：[e-mail]1ExperienceProcedureThealloysforthepresentinvestigationhavebeenpreparedinthevacuuminductionfurnaceandthecompositionsoftheHSLA-100steelwereshownintable1.Theingotwere200mminthickness,andthealloyweresoakedat1100~1200℃.Thediameteroftheworkingrollerswas750mm,andthebodiesoftherollswere500mm.Twostagecontrolrolledprocesswerecarriedoutandthefinishrollingtemperaturewere700~850℃,theplateswereaircooledordirectquenchingwiththeacceleratedcoolingequipmentbehindtherollerstand,themaximumcoolingratewere30℃/s.Theconventionalheattreatmentquenchedandtemperedwereconductedwithquenchingtemperature900℃andageingtemperaturefrom550℃to720℃.Theplatethicknesseswere16~40mm,andthewidthwas400mm.Thespecimensweretransversetotherollingdirectionsafterheattreatment.ThemechanicalpropertiesweremeasuredwiththetestspecimensaccordingtothestandardofJWAS5andtheCharpyVnotchimpactspecimenswere10×10×55mminsize.ThetransformationtemperatureandtheCCTcurveweremeasuredwiththethermalsimulationtesterThermecmastor-Z,thecoolingrateswerefrom0.2℃/sto30℃/s,andbaseonthedatethesuitablerollingparametersandheattreatmentparametersweredetermined.Table1ChemicalcompositionsofHSLA-100steel(wt，％)SteelCSiMnPSAlCuNi、Cr、MoNbCeqPcmHSLA-1000.050.290.870.0070.00320.0261.52added0.0210.7580.3040.040.280.880.0070.0050.0291.52added0.0340.7470.293Note:6515MnCrMoVCuNiCeqC53020601510SiMnCuCrNiMoVPcmCB2ResultsandDiscussion2.1TransformationTemperatureandCCTcurveThetransformationtemperatureoftheHSLA-100steelweredeterminedfromthecurveofheatingandcoolingprocess,theAC3temperatureis790℃,andtheAr1temperatureis470℃,thetransformationstructurearefullymartensitefromtheCCTcurve,evenatthelowercoolingratearemartensite,itprovedthatthehardenabilityofthesteelarewell,withtheincreaseofthethicknessthefullymartensitestructurewerefoundinthecoreoftheplate,itindicatethatitwassuitableforthevariousquenchingprocesswiththethicknessincreasing.Fig1StaticCCT(continuouscoolingtransformation)CurveofHSLA-100steel2.2ResultsofreheatingquenchedandtemperedprocessThemechanicalpropertiesresultsofreheatingquenchedandtemperedprocessareshownintable2,itshownthatthesteelshavehighstrengthandhightoughnessatlowtemperature.Theplatesthicknessare16、25and40mm,theimpactabsorbenergyat-85℃arerespectively220~258Jand184~250J,theareaoftheshearfracturearefullyductility.FromtheSEMoffractographyarefullydimple,itshownthesteelshavegoodtoughnessatlowtemperature.Table2ThemechanicalpropertiesresultsofreheatingquenchingandtemperedGauge,mmYS,MPaTS,MPaA,%Z,%Akv,JFA,%-85℃-100℃-85℃-100℃Standard≥690record≥20≥811675075085085523.526.568.571.512611710811713210210010010010085902573073080079522.522.577.577.02502582372372432371001001001001001002573574085085022.522.574.074.5237213222189211228100100100801001004071069581081026.026.078.078.022223425021520