Heat-treatment-process教學(xué)講解課件

1Heattreatment1.IntroductionThekeytoimprovethematerialpropertyistochangeitsstructureatatomiclevel.Thiscanbeachievedthrough(i)alloyingand(ii)controlledheatandcoolingbasically–heattreatmentThebasicstepsofheattreatmentare: Heat->Soaking->Cooling2Heattreatment Heat->Soaking->CoolingTemperature TimeofsoakingRateofcooling Mediumofcooling-Differentcombinationsoftheaboveparameters-DifferentcompositionsofmaterialsandinitialphasesofmaterialsDifferentheattreatments3Heattreatment2.PurposeofheattreatmentSoftenthemetalprior(before)toshaping;Relieve(ease)theeffectsofstrainhardeningthatoccursduringcoldforming;Achievethefinalstrengthandhardnessrequiredinthefinishedproductasoneoftheendmanufacturingprocesses.4HeattreatmentHeattreatmentBodyheattreatmentSurfaceheattreatment3.Classificationofheattreatmentprocesses(forbasicsofengineeringtechnology)AnnealingMartensiteformationinsteelSurfacehardening5Heattreatment4.AnnealingHeat->Soaking->CoolingReducehardnessandbrittlenessAltermicrostructurefordesiredmechanicalpropertiesSoftenmetalstoimproveformabilityRecrystalizecoldworked(strainhardened)metalsRelievestressfromshaping6Heattreatment4.Annealing

Fullannealing(heatingalloyintoausteniteregionandslowcoolinginfurnacetoformcoarsepearlite)

Normalizing(coolingatfasterrates,coolinairresultedinfinepearlite,highstrengthandhardness)

ProcessAnneal(toallowfurthercoldworkingofpart)-Re-crystallizationanneal(fullrecoveryofcoldworkedmetal)-RecoveryAnneal(partialreturnofgrainstructure)

Stress-reliefannealing(reducedistortionanddimensionalvariations)8Heattreatment5.TTTcurve–principleforMartensiteFormation

eutectoidcomposition

preheatorheatupalloytoaustenite.austenitetovariousphases:coolingrate.Pearlite,P;Bainite,B:alternativeformsof ferrite-carbidemixturesMartensite,MHandouts29Metals–PhasediagramforIronandCarbonFe3CEutecticEutectoid105.TTTcurve–principleforMartensiteFormationTime-----x-axis;temperature---y-axisCurveinterpretedbystartingat0inausteniteregionaboveA1=1333FProceedingdownwards&totherightalongatrajectoryThisisforspecificcompositionofC(0.80%)TrajectoryproceedsthroughregionindicatingtransformationintopearliteorbainiteTTTdiagramshowsbothstartsandfinishf

linesPearlite(ferrite+Carbide)

---showsslowcoolingfromaustenite----itpassesthroughPsabovenoseofTTTcurveBainite(ferrite+Carbide)----rapidcoolingtosomewhataboveMs-----NoseofTTTcurveisavoided-----MuchslowercoolingtopassthroughBsandintoferrite-carbideregionIfcoolingoccursatmuchfasterrate,austenite-----martensiteBCCtoBCT

1112Heattreatment5.TTTcurve–principleforMartensiteFormationMartensite:hardandbrittle BCT+carbonTetragonalMsmeansthetemperatureMstartstoform.Msdependsonalloyedelement;somearelowerthanroomtemperature13Heattreatment5.HeattreatmenttoformMartensitephaseAustenitizing:heatuptoacertaintemperaturetoformQuenching:coolingmedia:

Brine:thefastest;

Air:theslowestTempering:Heatuptotemperaturebeloweutectoid

soakforonehour&slowcoolingBCTtoBCC145.HeattreatmenttoformMartensitephaseAustenitizing–quenching-tempering15Heattreatment5.Hardenability-Therelativecapacityofasteeltobehardenedbytransformationtomartensite;hardnesspenetrationHardenability=Hardness?alloyingelementsincreasethehardenability:tomakeTTTcurveright:toincreasethetimetostartthetransformationforAustenitetoMartensite166.SurfaceheattreatmentThermochemicaltreatmentCompositionofpartsurfacealteredbyadditionofotherelementsAddingofcarbon,nitrogen,orotherelementsCarburizingNitridingCarbonitriding17SurfaceheattreatmentPackcarburizing-Packcarbonaceousmaterials(charcoal);VerythickhardouterlayerGascarburizing-DiffuseHydrocarbonfuels(propaneinafurnace);thinhardouterlayerLiquidcarburizing-Diffusemoltensaltbathcontainingsodiumcyanide,bariumchloride,andothercompounds;mediumsizedhardouterlayer-Carburizing-Lowhardness-DuctileCapableofwithstandingstress18SurfaceheattreatmentCarburizing->HRC60,Thickness:0.025–4mmNitriding->HRC70,Thickness:0.025–0.05