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外文翻译---根据高速钢不同的加工条件T42冶金粉末烧结机制和微观结构的发展.doc

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外文翻译---根据高速钢不同的加工条件T42冶金粉末烧结机制和微观结构的发展.doc

1SinteringbehaviourandmicrostructuredevelopmentofT42powdermetallurgyhighspeedsteelunderdifferentprocessingconditionsHighspeedsteelpowdersT42gradehavebeenuniaxiallycoldpressedandsubsequentlydensifiedthroughdifferentsinteringroutesincludingsupersolidusliquidphasesinteringSLPSundervacuumanddifferentnitrogenpressures0.2,0.9,and8barandthroughsolidstatesinteringSSSbyhotisostaticpressingHIP.HIPtemperaturesaslowas850°Cledtonearfulldensificationofthematerial98theoreticaldensitywithaveragesizeofM6CandMCcarbideslowerthan1μmandgrainsize≈3μm.Pressurelesssinteringunderdifferentnitrogenpressuresupto0.39wt.NabsorptionledtoasignificantreductionoftheoptimumsinteringtemperatureOSTandapronouncedincreaseinthesinteringwindowSWascomparedtovacuumsintering.Pressurelesssinteringunder8barN2ledtoafurtherreductioninOSTtogetherwiththeprecipitationofmassiveeutecticstructures.Therefore,theSWwasjudgedtobenegligible.TheresponseoftheassinteredmaterialstotheheattreatmentisbasicallydeterminedbytheamountofCavailableinthematrixpriortoquenchingandthegrainsize.Thehighesthardnessachievableforthesinteringconditionsevaluatedranges700–1100HV2afteraustenitizingat1100°C,oilquenchingandmultitemperingat500–550°C.Toolsteelsservealargerangeofapplicationsincludinghotandcoldworkingofmetalsandinjectionmouldingofplasticsorlightalloys.HighspeedsteelsHSSaremorespecificallyusedascuttingtoolsandwearparts.Morerecently,thesematerialshavealsobeenusedforstructuralapplications.Thehighperformanceexhaustvalveseatinsertsforpassengervehiclesconstitutethemostnotableexample1.Ingeneralterms,forthesestructuralapplications,acombinationofhighstrength,wearresistanceandhardnesstogetherwithanappreciabletoughnesscomparedwithothermaterialsusedastoolsandfatigueresistanceisrequired.Fromamicrostructuralpointofview,HSScanbedescribedasmetallicmatrixcompositesformedbyaferrousmatrixwithadispersionofhard,wearresistantcarbides.Thetype,size,morphology,distributionandvolumefractionofcarbidesaswellasthecharacteristicsoftheferrousmatrixdependonboththecompositionofthematerialandthemanufacturingprocess2and3.Thebasicalloyingelementsofhighspeedsteelsareapproximately15–30wt.ofcarbideformersCr,Mo,W,V,sometimesCoand2sufficientcarbontopromotetheformationofcarbides.TungstenandmolybdenummainlycontributetotheformationoftheprimaryM6CandM2CcarbidesandvanadiumisthemainconstituentoftheMCtype.ConventionalmanufacturingprocessesfortheproductionofcomponentswiththesematerialsincludewroughtmetallurgyandpowdermetallurgydirectsinteringandhotisostaticpressingHIP.Themainmanufacturingstepsforwroughtprocessingaremelting,casting,hotworking,machiningandheattreating.Normally,extensivehotworkingareareductions90isnecessarytodispersethecarbidenetworksformedduringthesolidificationoftheascastingots.Thishotworkingprocessleadstothealignmentofcarbideinstrings,whichisresponsibleforanisotropicproperties2.PowdermetallurgyPMtechniqueswereinitiallydevelopedtoovercometheseproblems.Thestartingrawmaterialsareprealloyedgasorwateratomisedpowders.Gasatomisedpowdersarecleanerthanwateratomisedpowdersandbothofthemarefreeofsegregationsduetothehighcoolingratesinvolved.GasatomisedpowdersareusedforHIP4andpowderinjectionmouldingPIM5.HIPisdevotedforaprimequalityproductduetothecleannessoftherawmaterialandtothefactthatdensificationtakesplacebyasolidstatesinteringSSSprocess.Consequently,afineandhomogeneousdistributionofcarbidesembeddedinaporefreeferrousmatrixisobtainedleadingtoexceptionalproperties.PIMisbestsuitedforsmallcomponentswithcomplexgeometriesanddensificationtakesplacebydirectsinteringi.e.,pressurelesssinteringthroughasupersolidusliquidphasesinteringSLPSmechanism5and6.Wateratomisedpowdersarenormallyprocessedbythedirectsinteringroute.Partialdensificationisachievedbycoldpressingthepowderswithasuitablecompactionlubricant.Subsequently,sinteringtofulldensitytakesplacebyaSLPSmechanism.Thedirectsinteringroutehasinherentadvantagesintermsofachievablepropertiesversusprocessingcostsandenvironmentalconsiderationsrelatedtothehighlyefficientmaterialuse.Duringthelast20years,ahighresearchefforthasbeenmainlyaddressedattheunderstandingofthephysicalandchemicalmechanismsinvolvedinthedensificationviaSLPS7andSSS4.Additionally,researchhasalsobeenfocusedonthemicrostructuralchangesoccurringduringheattreatmentsleadingtothedesiredmechanicalpropertiesi.e.,strength,toughness,wear,fatiguedependentontheserviceapplications8.3Previousstudies9,10,11and12havebeenfocusedontheoptimisationofthedirectsinteringrouteofHighVanadiumHSSgradesmainlyM35MHVbyunderstandingtheeffectofthesinteringatmosphere.Thisapproachhasledtoasignificantdecreaseofthesinteringtemperaturesneededforfulldensificationinnitrogenrichatmospherescomparedtovacuumsintering.TheoptimumsinteringtemperatureOSTforM35MHVdecreasedfrom1220°Cforvacuumsinteringto1140°Cwhensinteredundernitrogenrichatmosphere3and10.Theeffectofboththesinteringatmosphereandalloymodificationsi.e.,carbonadditionshasbeenunderstoodbytheuseofcomputationalthermodynamicscalculationofmulticomponentphasediagrams10and11.Moreover,thecorrespondencebetweencomputationalthermodynamicsandexperimentaldataconstitutedapreliminarystepforalloydesignofnewHSScompositions12and13.ThepresentstudyisaimedatthedescriptionofthesinteringbehaviourofthePMT42gradeunderdifferentnitrogenpressures.ThismaterialhasbeenchosenfortheinvestigationsinceitisacommercialgradecontaininganadequateamountofVformicrostructuraldesignthroughtheadditionofN.Additionally,theexcellenthothardnessofT42duetothe10.58wt.Co,makesthismaterialveryinterestingforbothstructuralandtribologicalapplications.ThesatisfactoryresultsofearlierinvestigationsonthesinteringbehaviourofT42inNrichatmospheres9invitedforamoredetailedinvestigationstrivingforacommercialimpactoftheresearch.ThemainobjectivewasthemicrostructuraldesignofPMHSSthroughthedensificationrouteandtheheattreatmentsequenceselected.Awidesetofdifferentmicrostructureshasbeenobtainedbyusingthedifferentsinteringconditions.TheeffectoftheassinteredmicrostructuremainlyabsorbedNcontentandgrainsizeontheheattreatmentaustenitizingquenchingmultitemperingisalsodiscussed.References1H.Kawata,K.Hayashi,K.Ishii,K.Maki,A.EhiraandM.Toriumi,SAETrans.10751998,pp.194–200.2G.Hoyle,HighSpeedSteels,Butterworths,BoroughGreen,SevenoaksKent1988.3S.GimenezandI.Iturriza,J.Mater.Process.Technol.143/1442003,pp.555–560.44E.Arzt,M.F.AshbyandK.E.Easterling,Metall.Trans.A14A1983,pp.211–2215Z.Y.Liu,N.H.Loh,K.A.KhorandS.B.Tor,Mater.Lett.452000,pp.32–38.6B.Levenfeld,A.VarezandJ.M.Torralba,Metall.Mater.Trans.A3362002,pp.1843–1851.7R.M.German,Int.J.PowderMetall.2611990,pp.23–34.8G.Krauss,HeatTreatmentandProcessingPrinciples6thed.,ASMInternational2000.9R.H.Palma,V.MartinezandJ.J.Urcola,PowderMetall.3241989,pp.291–299.10I.Aguirre,S.Gimenez,T.GomezAcebo,S.TalacchiaandI.Iturriza,PowderMetall.4432001,pp.211–220.11I.Aguirre,S.Gimenez,T.GomezAcebo,S.TalacchiaandI.Iturriza,PowderMetall.4241999,pp.353–357.12S.GimenezandI.Iturriza,PowderMetall.4632003,pp.209–218.13V.Trabadelo,S.Gimenez,T.GomezAceboandI.Iturriza,ScriptaMater.5332005,pp.287–292

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