热处理手册

HeatTreatmentThirugnanamKSEAMaterialsEngineeringFundamentalsofHeatTreatmentforMetallicMaterialsIntroductionThepurposeofthispresentationistoprovideabasicunderstandingofthemetallurgicalprocessesassociatedwiththeheattreatmentofmetallicmaterials.ThermalProcesses:1.ShapechangeofmaterialsSuchasforging,forming,extrusion,rolling,weldingandcasting(foundry).2.NoshapechangeofmaterialsSuchasheattreatmentandcoating.Liquidwaterandicearefamiliarexamplesofhowamaterialcanexistinvariousforms.Steelalsoexistsinvariousforms,includingseveraldifferentsolidforms.VariousformsofmaterialWhatisHeattreatment?•Answer:Thecontrolledheatingandcoolingofmaterialsforthepurposeofalteringtheirstructuresandproperties.Purposesofperformingaheattreatmentprocessonametalliccomponent•Modificationofthemicrostructureforimprovementofmachining,coldformingprocesses.•Obtainingtherequiredmechanicalproperties,suchasstrength,toughness,hardness,wearresistanceandfatiguelifebasedonapplication.•Reductioninbrittleness,residualstress,dimensionalinstabilityofcomponents.•Surfaceprotectionfromenvironment,suchasoxidation,corrosionmediumandstresscorrosion.FundamentalsofHeatTreatmentProcessingDevelopmentforMetallicComponentsWhenamaterialisselectedperdesignrequirementsandapplication,thenextstepishowtohavethedesignedpartssatisfytheserequirements,suchasmechanicalproperties(strength,hardness,toughness,residualstressstateandfatiguestrength)andmicrostructure.Theyareachievedthroughaproperheattreatmentprocess.Howtodevelopaheattreatmentprocess???Toolone:Fe-CarbonphasediagramForheatingabovetheaustenitizingtemperatureTooltwo:T-T-TorITcurveofselectedmaterialDeterminationofcoolingrate(reductionofcrackingriskanddistortion)toobtaintherequiredmicrostructure.Iron-CarbonphaseDiagramSincesteelisaFe-Cally,thecarbonisakeyelementinanygradesofsteel.MostalloyingelementsinthesteelsareCr,Mo,Ni,Si,Mn,aswellasVandW.•AllofthemchangethepositionsoftheA1,A3andAmboundariesandtheeutectoidcompositionwillbechanged.•Allimportantalloyingelementsdecreasetheeutectoidcarboncontent.Forexample,1080(0.8%C)steeliscalledhyper-eutectoidsteel.However,H19(0.3%C)ishyper-eutectoidsteelduetoadditionofCr(2%),W(8%)andV(1%).EutectoidpointshiftstowardtoleftintheFe-Cdiagram.•Austenite-stabilizingelements(MnandNi)decreaseA1temperature,i.e.,expendγgammazone.•Ferrite-stabilizingelements(Cr,Si,Mo,W,VandTi)increaseA1temperature,i.e.,shrinkγgammazone.•TheeffectofcombinationofalloyingelementsontheFe-Cdiagramisverycomplicated(mayexpandorshrinkgammazone).EffectsofalloyingelementsontheFe-Cphasediagram1.1035steel–1570F(855C)2.1040steel–1555F(845C)3.4340steel–1570F(855C)4.5130steel–1570F(855C)5.8620steel–1600–1700F(870–925Cforcarburizing)6.H19steel–2005-2200F(1095–1205C)7.D2steel–1795-1875F(980-1025C)8.T2steel–2300-2375F(1260-1300C)ExamplesofaustenitizingtemperaturedevelopmentforsteelhardeningFullTTTDiagramThecompleteTTTdiagramforaniron-carbonalloyofeutectoidcomposition.A:austeniteB:bainiteM:martensiteP:pearliteEffectofthecarboncontentontheT-T-T-curveprofile1.MovethenoseofT-T-Tcurvetowardthelower-rightdirection.2.LoweringMspointtemperature(martensitictransformationstarttemperature).3.Increasinghardeningabilityorhardenabilityusingsamecoolingrate.EffectoftheAlloyingelementsontheT-T-T-curveprofileA0.42C0.20Mn0.21MoB0.48C0.94Mn0.25MoC0.36C0.17Mn0.82MoFE0.23C0.82Mn1.22Cr0.53Mo0.22V1.MostofthemmovethenoseofT-T-Tcurvetowardthelower-rightdirection.2.SomeofthempromotetheformationoftwonosesinT-T-Tcurves3.SomeofthemlowerMstemperaturepoint(martensitictransformationstarttemperature).4.Mostofthemincreasehardeningabilityorhardenabilityusingsamecoolingrate.F1.5C12Cr1Mo1VD0.39C0.56Mn0.34Ni0.74MoSoWhat’saCCTDiagram?•PhaseTransformationsandProductionofMicroconstituentstakesTIME.•HigherTemperature=LessTime.•Ifyoudon’tholdatonetemperatureandallowtimetochange,youare“ContinuouslyCooling”.•Therefore,aCCTdiagram’stransitionlineswillbedifferentthanaTTTdiagram.SlowCoolingTimeinregionindicatesamountofmicroconstituent!MediumCoolingCoolingRate,R,isChangeinTemp/Time°C/sFastCoolingThissteelisveryhardenable…100%Martensitein~1minuteofcooling!HeatTreatmentcanbeconsideredintermsofthreeaspects1.Incrystallographicchange2.Inmicrostructurechange3.Inmechanicalandphysicalpropertychange•IncrystallographicchangeFromBCCtoFCCtoBCTBCCFCCBCTBCC–BodycenteredcubicFCC–FacecenteredcubicBCT–Bodycenteredtetragonal•InmicrostructurechangeFrompearlitetoaustenitetomartensitethroughquenching(fastcooling)Inmechanicalproperties,suchashardnessSAE1050SAE4147HeatTreatmentProcessTreeHeatTreatment(Heating,Holding&Cooling)AnnealingNormalizingThroughhardeningCasehardening•Stressreliefannealing•Recrystallizationannealing•Spheroidizedannealing•Isothermalannealing•Quenching&tempering•Interruptedquenching•Isothermal•Austempering•Martempering•Vacuum•Inductionhardening•Flamehardening•Laserhardening•Carburizing•Carbonitriding•NitrocarburizingFULLANNEALING•Itconsistsofheatingsteeltoausteniticregion(790-900°C),followedbyslowcooling,preferablyinthefurnaceitselforinanygoodheat-insulatingmaterial.Fullannealing8620ASRA