机械全APS

一、EngineeringMaterialsandHeatTreatmentThislesson,istudyengineeringmaterialsandheattreatment.Engineeringmaterials,istudysteelandcastiron,includeiron-carbonphasediagram.Heattreatment,istudynormalizingquenchingtemperingandannealing.Iron-carbonphasediagram,showingthetemperatureandcarbonrangesforcertaintypesofheattreatments.Withthecarbonrise/increase,materialsbecomemoreandmorebrittle,strengthincrease,hardnessincrease,butplasticitydecrease.ABCD---liquidline,upisliquidzoneAHJECF---solidline,downissolidzoneHJB---peritecticline,whenthecarbonrangefrom0.09percentto0.53percent,materialscooldownthisline,itwillperitectictransformationECF---eutecticline,whenthecarbonrangefrom2.11percentto6.69percent,materialscooldownthisline,itwilleutectictransformationproduceledeburite.PSK---eutectoidline,whenthecarbonrangefrom0.0218percentto2.11percent,materialscooldownthisline,itwilleutectoidtransformationproducepearlite.Ferrite:aninterstitialsolidsolutionofcarboninFeα,atroomtemperatureferriteisductilebutnotverystrong.Austenite:aninterstitialsolidsolutionofcarboninFeγCementite:acompoundofcarbonandFeSteelisanalloyofcarbonandironandotheralloyingelements(e.g.Mn,Si)withcontentupto2.11%intendedforwroughtproductsorsemi-products.Castironisanalloyofcarbonandironandotheralloyingelements(e.g.Mn,Si)withcarboncontentover2.11%intendedforcasting.Perliteisastructure(i.e.Consistsoftwophases)consistsofalternatelayersofferriteandcementite[intheproportion87:13byweight]Perliteisformedfromausteniteateutectoidtemperature(A1)727℃uponslowcooling.Therearethreegroupsofsteelsaccordingtocarboncontent:Hypoeutectoidsteelscontaininglessthan0.77%CEutectoidsteelswithcarboncontentabout0.77%Hypereutectoidsteelscontainmorethan0.77%C(upto2.11%C)Ledeburiteisastructure(i.e.Consistsoftwophase)consistsofalternatelayersofausteniteandcementite.Ledeburiteisformedfromliquidateutectictemperature1148℃uponslowcooling.Fromeutectictemperature1148℃toeutectoidtemperature727℃,ledeburiteiscalledbyhightemperatureledeburite.Beloweutectoidtemperature727℃，ledeburiteiscalledbylowtemperatureledeburite.Therearethreegroupsofcastironaccordingtocaarboncontent:Hypoeutecticcastironcontaininglessthan4.3%C(upto2.11%C)Eutecticcastironwithcarboncontentabout4.3%Hypereutecticcastironcontainmorethan4.3%C(upyo6.69%C)NormalizingHeatthesteeltoacertaintemperature,keepthetemperatureforaperiodoftime,thenputitintheair,slowlycoolittotheroomtemperature.CertaintemperatureisaboveAC3orACm,from30℃to50℃。Carbonsteelheatedtoapproximately55℃aboveAC3orACmfor1hour,thisassuresthesteelcompletelytransformstoaustenite.Thesteelisthenair-cooled,whichisacoolingrateofapproximately38℃perminute.Thisresultsinafinepearliticstructure,andamore-uniformstructure.Normalizingsteelhasahigherstrengththanannealedsteel,ithasarelativelyhighstrengthandductility.QuenchingHeatthesteeltoacertaintemperature,keepthetemperatureforaperiodoftime,thenputitintowateroroil,makeittobecooledquicklytotheroomtemperature.CertaintemperatureisaboveAC3orAC1,from30℃to50℃。Carbonsteelwithatleast0.4%Cisheatedtonormalizingtemperatureandthenrapidlycooled(quenched)inwater,brineoroiltothecriticaltemperature.Quenchedsteelisextremelyhardbutbrittle,usuallytoobrittleforpracticalpurposes.Theseinternalstressescausestresscranksonthesurface.Quenchedsteelisapproximatelythreetofourfoldharderthannormalizedsteel.TemperingHeatthequenchedtobemartensitesteeltoacertaintemperature,keepthetemperatureforaperiodoftime,thencoolittotheroomtemperatureintheair.CertaintemperatureisbelowAC1150℃~260℃370℃~650℃Temperinginvolvesreheatingquenchedsteeltoatemperaturebelowtheeutectoidtemperaturethencooling.Function:1.Improvesductilityandtoughness2.Reducecranking3.Improvesmachinability4.Increaseimpactresistance5.ImprovesmalleabilityTemperingintherangeof260℃~370℃issometimesavoidedtoreducetemperingbrittling.Lowtempering150℃~260℃1moldAveragetempering370℃~500℃5springHightempering500℃~650℃3gearAnnealingHeatthesteeltoacertaintemperature,keepthetemperatureforaperiodoftime,putitinthefurnaceslowlycoolittoroomtemperature.Annealingisusedtoinduceductility,softenmaterial,relieveinternalstresses,refinethestructurebymakingithomogeneous,andimprovecoldworkingproperties.Processannealing500℃~650℃restoressomeoftheductilitytoaworkpieceallowingitbeworkedfurtherwithoutbreaking.Fullannealing.Carbonsteelisheatedtoapproximately40℃aboveAc3orAc1for1hour,thisassuresalltheferritetransformsintoaustenite.Thesteelmustthenbecooledslowlyintherealmof38℃perhour.Usuallyitisjustfurnacecooled,wherethefurnaceisturnedoffwiththesteelstillinside.Thisresultsinacoarsepearliticstructure,whichmeansthebandsofpearlitearethick.Fully-annealedsteelissoftandductile,withnointernalstresses,whichisoftennecessaryforcost-effectiveforming.Onlyspheroidizedsteelissoferandmoreductile.Spheroidizing.Spheroidizeformswhencarbonsteelisheatedtoapproximately700℃forover30hours.Theresultsisastructureofrodsorspheresofcementitewithinferriteorpearlite.Thepurposeistosoftenhighercarbonsteelsandallowmoreformability.二、Mechanicsofmaterials(问过此课程)Inmaterialsscience,thestrengthofamaterialref