Influence-of-hot-press-forming-techniques-on-prope

Availableonlineatw.sciencedirect.comScienceDirectJOURNALOFIRONANDSTEELRESEARCH,INTERNATIONAL.2011,18(5):59-63InfluenceofHotPressFormingTechniquesonPropertiesofVehicleHighStrengthSteelsCHANGYing,MENGZhao-huan,YINGLiang,LIXiao-dong,MANing,HUPing(SchoolofAutomotiveEngineering,StateKeyLaboratoryofStructuralAnalysisforIndustrialEquipment,DalianUniversityofTechnology,Dalian116024,Liaoning,China)Abstract:Basedonthecombinationofmaterialsscienceandmechanicalengineering,hotpressformingprocessofthevehiclehighstrengthsteelswasanalyzed.Thehotformingprocessincluded:heatingalloysrapidlytoaustenitemi-crostructures,stampingandcoolingtimely,maintainingpressureandquenching.Theresultsshowedthatmostofaustenitemicrostructurewaschangedintouniformmartensitebythehotpressformingwhilethesampleswereheatedat900'Candquenched.Theoptimaltensilestrengthandyieldstrengthwereupto1530MPaand1000MPa,re-spectively,andtheshapedeformationreachedabout23%.Andspringbackdefectdidnothappeninthesamples.Keywords:highstrengthsteel;lightweight;hotforming;martensiteAsaneffectiveeconomicalenergymeasure,thelightweightdevelopmentdirectionofautomobilehasbecomeoneofthemostimportantresearchsubjectsintheautomotiveindustry.Therearethreemajorwaystoachieveautomobilelightweight:optimizingvehicleframesandstructures;makingvehiclebodyorframeofnewandalternativematerialstoreducethevehiclemass(Thehighandultrahighstrengthsteelcanbeusedasalternativematerialsbecauseofitsthinnerthickness);adoptingadvancedmanufac-turingtechniquesforthesakeofautomobilelight-weight,suchasthickness-gradienthighstrengthsteel(HSS)ormetalbasedcompoundplatesbycontinuouspressingorhotpressforming].Al-thoughHSShasbeenappliedinsomedomestictop-gradevehicles,thekeyproducingtechnologieshavealwaysbeendominatedbyforeigncompanies,suchasAcelorCompany,soastoraisetheproductcostobviously.Bydomesticself-designedhotpressformingtechniquesandwater-coolingmould,theautomobileHSScanbeproducedtosubstitutefor-eignvehicleparts.Ingeneral,withtheenhancementofsteelblank'smechanicalstrength,itsformabilityiswors-eneddramatically.Itisdifficulttoapplythetradi-tionalcoldstampingtechnologyintothefieldofpressingHSS.Thus,thehotstampingtechnologyofmartensiticsteelblankisappliedasanewtech-nology,whichcombinesmetalthermoplasticform-ingmethodandwater-coolingmouldquenchingprin-ciple.Inthispaper,boronsteelblankwasformedandwater-coolingmouldwasquenchedsimultane-ouslyduringtheprocessofhotstamping.Comparedwithoriginalautomobilepearlitesteel['],theauto-mobileHSSobtainedbyadvancedhotpressformingtechniquecanreduceabout30%ofthetotalvehiclemassandachievecomplexgeometries,highsecurityandmechanicalstrength.Thereasonisthatausten-itemicrostructurewithoptimalplasticityandductili-tycanbeobtainedbyhotpressformingathightem-perat~re[~-~',andtheHSSwithbothexcellentme-chanicalpropertiesandlightweightwillbeobtainedafterbeingformedandquenchedC6-*].Theapplica-tionofhot-formedthinnerHSSplateswillbecomeanimportantmeasuretorealizevehiclelightweight.1ExperimentalSetupInordertoformHSSathightemperature,andFoundationItem:ItemSponsoredbyNationalNaturalScienceFoundationofChina(50901011);NationalScienceFundforDistinguishedYoungBiography:CHANGYing(1978-),Female,Doctor;E-mail:[e-mail];ReceivedDate:June28,2010ScholarsofChina(10125208);LiaoningProvinceDoctorStartupFundofChina(20071090)60JournalofIronandSteelResearch,InternationalVol.18toavoidcracksandspringback,thesamplesneedcharacterornospringbackdefectisanobviousad-rapidheatingandtransformcompletelyintostablevantage,andmostofmicrostructureinthesampleisaustenitemicrostructure.Andthen,samplesaremartensite.Thethicknessofsampleis1.6mm,andpressedandcooledinself-madewater-coolingmould.themainelementsofHSSinthisexperimentareFortheobtainedHSSsample,itsshape-freezingshowninTable1.Table1Mainelementsofmaterialintheexperiment22MnB5CMnCrSiBPSA10.020Minimum0.2201.2000.1100.2000.002Maximum0.2501.4000.2000.3000.0050.0200.0050,050--Actualexperimentalprocedureincluded:1)setdifferentheattreatmenttemperaturesintherangeof750to1000'C;2)putthesampleintotheheattrea-tedfurnacetobeheatedfor4minatacertaintem-perature;3)removeitbymechanicalhandandputitintothehotformingmouldstobepressedquickly;4)simultaneously,itwaswater-cooledatabout30C/sinthemound.Themechanicalpropertiesofsamplewereanalyzedbytensiletestsystemandthemicrostructureappearancewasanalyzedbymetallo-graphicanalysisdevice.TheshapeandsizeoftestsampleareshowninFig.1.04206R6306L4~L=60Unit:mmFig.1Theshapeandsizeofspecimen2ResultsandDiscussionMechanicalpropertiesofHSS(boronsteels)withdifferentthicknesses(1.0mm,1.6mm,2.0mm,2.5mm,3.0mmand4.0mm,respectively)werechecked(GBT16865-1997wasconsulted,andsam-pleswereselectedalongO,45and90rollingdirec-tionrespectively).Theunidirectionaltensiletests(basedonthemetaltensiletestingstandardofGBT228-2002)werefinished.ComparedwithUSI-BOR1500,thevaluesofbasicmechanicalpropertiesforHSSwithdifferentthicknessesintheexperimentareshowninFig.2.Fig.2showsthatafterwater-coolingquench-ing,thetensilestrengthandyieldstrengthofsam-ples(excepttheonewiththicknessof4.Omm)rea