机械类英语论文翻译.docx

机械类英语论文翻译.docx

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机械类英语论文翻译

InfluenceofHotPressFormingTechniquesonPropertiesofVehicleHighStrengthSteels

（SchoolofAutomotiveEngineering,StateKeyLaboratoryofStructuralAnalysisforIndustrialEquipment,

DalianUniversityofTechnology,Dalian116024,Liaoning,China）

Abstract:

Basedonthecombinationofmaterialsscienceandmechanicalengineering,hotpressformingprocessofthevehiclehighstrengthsteelswasanalyzed.Thehotformingprocessinclud-ed:

heatingalloysrapidlytoaustenitemicrostructures,stampingandcoolingtimely,maintainingpressureandquenching.Theresultsshowedthatmostofaustenitemicrostructurewaschangedintouniformmartensitebythehotpressformingwhilethesampleswereheatedat900。

Candquenched.Theoptimaltensilestrengthandyieldstrengthwereupto1530MPaand1000MPa,respectively,andtheshapedeformationreachedabout23%.Andspringbackdefectdidnothapp-eninthesamples.

Keywords:

highstrengthsteel;lightweight;hotforming;martensite

Asaneffectiveeconomicalenergymeasure,thelightweightdevelopmentdirectionofautomo-bilehasbecomeoneofthemostimportantresearchsubjectsintheautomotiveindustry.Therearethreemajorwaystoachieveautomobilelightweight:

optimizingvehicleframesandstruc-tures;makingvehiclebodyorframeofnewandalternativematerialstoreducethevehiclemass（Thehighandultrahighstrengthsteelcanbeusedasalternativematerialsbecauseofitsthinnerthickness）;adoptingadvancedmanufacturingtechniquesforthesakeofautomobilelightwei-ght,suchasthickness-gradienthighstrengthsteel（HSS）ormetalbasedcompoundplatesbycon-tinuouspressingorhotpressforming[1].AlthoughHSShasbeenappliedinsomedomestictopgradevehicles,thekeyproducingtechnologieshavealwaysbeendominatedbyforeigncompan-ies,suchasAcelorCompany,soastoraisetheproductcostobviously.Bydomesticself-designedhotpressformingtechniquesandwater-coolingmould,theautomobileHSScanbeproducedtosubstituteforeignvehicleparts.

Ingeneral,withtheenhancementofsteelblank，smechanicalstrength,itsformabilityisworseneddramatically.ItisdifficulttoapplythetraditionalcoldstampingtechnologyintothefieldofpressingHSS.Thus,thehotstampingtechnologyofmartensiticsteelblankisappliedasanewtechnology,whichcombinesmetalthermoplasticformingmethodandwater-coolingmouldquenchingprinciple.Inthispaper,boronsteelblankwasformedandwater-coolingmouldwasquenchedsimultaneouslyduringtheprocessofhotstamping.Compared

withoriginalautomobilepearlitesteel[2],theautomobileHSSobtainedbyadvancedhotpressformingtechniquecanreduceabout30%ofthetotalvehiclemassandachievecomplexgeometries,highsecurityandmechanicalstrength.Thereasonisthataustenitemicrostructurewithoptimalplasticityandductilitycanbeobtainedbyhotpressformingathightemperature[3-5],andtheHSSwithbothexcellentmechanicalpropertiesandlightweightwillbeobtained

afterbeingformedandquenched[6-8].Theapplicationofhot-formedthinnerHSSplateswillbecomanimportantmeasuretorealizevehiclelightweight.

1ExperimentalSetup

InordertoformHSSathightemperature,andtoavoidcracksandspringback,thesam-plesneedrapidheatingandtransformcompletelyintostableaustenitemicrostructure.Andthen,samplesarepressedandcooledinself-madewater-coolingmould.FortheobtainedHS-Ssample,itsshape-freezingcharacterornospringbackdefectisanobviousadvantage,andmostofmicrostructureinthesampleismartensite.Thethicknessofsampleis1.6mm,andthemainelementsofHSSinthisexperimentareshowninTable1.

Table1Mainelementsofmaterialintheexperimen

22MnB5

C

Mn

Cr

Si

B

P

S

Al

Minimum

0.220

1.200

0.110

0.002

0.002

-

-

0.020

Maximum

0.250

1.400

0.200

0.005

0.005

0.020

0.005

0.050

Actualexperimentalprocedureincluded:

1）setdifferentheattreatmenttemperaturesintherangeof750to1000℃;2）putthesampleintotheheattreatedfurnacetobeheatedfor4minatacertaintemperature;3）removeitbymechanicalhandandputitintothehotformingmouldstobepressedquickly;4）simultaneously,itwaswater-cooledatabout30℃/sinthemound.Themechanicalpropertiesofsamplewereanalyzedbytensiletestsystemandthemicrostructureappearancewasanalyzedbymetallographicanalysisdevice.

TheshapeandsizeoftestsampleareshowninFig.1.

Fig1Theshapeandsizeofspecimen

2ResultsandDiscussion

MechanicalpropertiesofHSS（boronsteels）withdifferentthicknesses（1.0mm,1.6mm,2.0mm,2.5mm,3.0mmand4.0mm,respectively）werechecked（GBT16865-1997wasconsulted,andsampleswereselectedalong0℃,45℃and90℃rollingdirectionrespec-tively）.Theunidirectionaltensiletests（basedonthemetaltensiletestingstandardofGBT228-2002）werefinished.ComparedwithUSIBOR1500,thevaluesofbasicmechanicalpropertiesforHSSwithdifferentthicknessesintheexperimentareshowninFig2.

Fig2showsthatafterwater-coolingquenching,thetensilestrengthandyieldstrengthofsamples（excepttheonewiththicknessof4.0mm）reached1500MPaand1000MPa,respectively.Thevaluesofthestrengthweretwicebetterthanthoseofsamplesbeforequenching,andnearlythesametothoseoftheplatesofthickness1.75mmfromAcelorCompany（USIBOR1500showninFig1）.

Fig2Tensileandyieldstrengthofhighstrengthsteelswithdifferentthicknessesbeforeandafterquench–ing

Generally,hotpressformingofsamplesisoperatedabovetransitiontemperatureofmartensitemicrostructure.Theheatingtemperatureinthisexperimentwasintherangeof750to1000℃becauseittook3sorsoforthesamplestobedeliveredintheair.Andthen,basedonanalyzingtensilestrengthsRmofsamplesafterhot-formingatdifferenttemperatur-esandquenching,theoptimaltemperaturecanbefound.ItisshowninFig3.

Fig3Curveoftensilestrengthvspreheatingtemperature

FromFig3,itisobviousthatthevalueoftensilestrengthRmonlyreaches900MPaat750℃;theoptimalvalueis1530MPaat900℃,andthevaluewillfallastemperatureissetabove900℃.BasedonanalyzingmicrostructureandFe-Fe3Cphasediagram,sampleslayinthetransitionregionofferriteaustenitemicrostructurecoexistenceat750℃.Atthismoment,austenitehasappearedinmicrostructureofsamples,anditcanbetransformedintomartensitemicrostructurethroughwater-cooling.Sothemechanicalproperties,suchastensilestrengthandyieldstrength,willbeimproved.Thatistosay,tensilestrengthofsamplesisalittlehigherthanthatoforiginalones（Rmis600MPaorso）.Thecontentofaustenitebecomeslargerastemperatureisraised,andthetensilestrengthwillbeimprovedgradually.Asfaras22MnB5steelisconcerned,theaustenitizingtemperatureisabout880℃.AsFig3shows,ifsamplesareheatedrapidlyto900℃andaircooledfor3,austenitemicrostructuresareobtainedcompletely.Thensamplesarehotformedandwater-coolingquenched,thefractionofmartensitemicrostructureinsamplesismorethan95%,sothecurveshowsapeak.However,astemperatureexceeds900℃,becausesuperheatdegreeistoolarge,micrograinsgrowsolargethatthetensilestrengthwilldecrease.Thushightem-peratureaustenitemicrostructure（obtainedassampleswereheatedrapidly）andgrainrefinementarethemainfactorstodeterminethemechanicalpropertiesofhighstrengthsteel-s.Inthispaper,differentfromthatinthelab,theinteractionmechanismsofmoldingandwater-coolingsystemonsamplesproducedintheproductionlinecanobjectivelyshowthemanufacturingpropertiesandmicrostructurecharacterofproductsinmass.

Asfarasthesamplesareconcerned,Aistheinitialanduntreatedsample;Bisthesamplewhichwasheatedat900℃for4min;Cisthesampleafterheattreatmentandwater-coolingquenching.ThedeformationofA,BandCare32%,24%and6%orso,respectively.Generally,Aiscomposedofmainpearliteandasmallamountofferrite,the

toughnessofwhichisbetterthanmartensite,soitsdeformationisrelativelybetter.Biscom-posedwiththehigh-temperaturetransitionalmicrostructureofaustenite,whosetoughnessisalsobetterthanmartensite,anddeformationislargerthanthelatter.Ciscomposedofover95%martensiteandlittleaustensite.Owingtoitshigherstrength,toughnessandplasticityofmartensitearelower,thatistosay,deformationofCisthelowestInFig4,whenthesamplewasheatedfor4minandstretchedat900℃,stress-straincurveandtestforcedisplacementcurvewereobtainedrespectively.

FromFig4（a）,afterbeingheatedupto900℃,themicrostructureofsamplehasbeencompletelyturnedintoaustenite.Thevalueintheelasticdeformationstageofcurvewilltendtowardstheyieldpoint,followingtheaxialtestforcegraduallybeingincreased.Thatistosay,theobviousplasticdeformationofsamplewillbeginaftertheyieldpoint.Whenitiscontinuouslystretchedtillthepeakpointofcurve,theneckingofsamplewilloccur.Passingthepeak,thestress-strainrelationshipwillbecomemorecomplex.FromFig4（b）,afterthecorrespondingpeak,thetestforcewillbereduced,alongwiththedecreasingcross-sectionalareaofsampletillthefracture.Itcanbeseenthattheappropriatetoughnessandplasticdeformationpropertiesofaustenitizingsampleat900℃willhelpHSSbehot-formedtocomplicatevehicleparts.ItisaneffectivemeasuretoformHSSwithroom-temperaturemartensitemicrostructurecharacter,anditisa