热处理-铁碳相图-Fe3C-奥氏体,马氏体,铁素体 教育学习

IRONIRON-CARBONDIAGRAM,1,优选内容,IRONIRON-CARBONDIAGRAM,2,优选内容,Outline,IntroductionCoolingcurveforpureironDefinitionofstructuresIron-CarbonequilibriumphasediagramSketchTheIron-IronCarbideDiagram-ExplanationTheAustenitetoferrite/cementitetransformationNucleationElongation=40%in2in;HardnessRockwellC0orRockwellB90,9,优选内容,Definitionofstructures,Pearliteistheeutectoidmixturecontaining0.80%Candisformedat723Converyslowcooling.Itisaveryfineplatelikeorlamellarmixtureofferriteandcementite.Thewhiteferriticbackgroundormatrixcontainsthinplatesofcementite(dark).,10,优选内容,Definitionofstructures,PearliteAveragepropertiesare:Tensilestrength=120,000psi;Elongation=20%in2in.;Hardness=RockwellC20,RockwellB95-100,orBHN250-300.,11,优选内容,Definitionofstructures,AusteniteisaninterstitialsolidsolutionofCarbondissolvedin(F.C.C.)iron.Maximumsolubilityis2.0%Cat1130C.Highformability,mostofheattreatmentsbeginwiththissinglephase.Itisnormallynotstableatroomtemperature.But,undercertainconditionsitispossibletoobtainausteniteatroomtemperature.,12,优选内容,Definitionofstructures,AusteniteAveragepropertiesare:Tensilestrength=150,000psi;Elongation=10percentin2in.;Hardness=RockwellC40,approx;andtoughness=high,13,优选内容,Definitionofstructures,Cementiteorironcarbide,isveryhard,brittleintermetalliccompoundofironresponsibleforthehardnessofquenchedsteel,16,优选内容,TheIron-IronCarbideDiagram,AmapofthetemperatureatwhichdifferentphasechangesoccuronveryslowheatingandcoolinginrelationtoCarbon,iscalledIron-CarbonDiagram.Iron-Carbondiagramshowsthetypeofalloysformedunderveryslowcooling,properheat-treatmenttemperatureandhowthepropertiesofsteelsandcastironscanberadicallychangedbyheat-treatment.,17,优选内容,VariousFeaturesofFe-Cdiagram,PeritecticL+d=g,EutecticL=g+Fe3C,Eutectoidg=a+Fe3C,Phasespresent,L,Reactions,dBCCstructureParamagnetic,gausteniteFCCstructureNon-magneticductile,aferriteBCCstructureFerromagneticFairlyductile,Fe3CcementiteOrthorhombicHardbrittle,Max.solubilityofCinferrite=0.022%Max.solubilityofCinaustenite=2.11%,18,优选内容,ThreePhaseReactions,Peritectic,at1490deg.C,withlowwt%Calloys(almostnoengineeringimportance).Eutectic,at1130deg.C,with4.3wt%C,alloyscalledcastirons.Eutectoid,at723deg.Cwitheutectoidcompositionof0.8wt%C,two-phasemixture(ferrite&cementite).Theyaresteels.,19,优选内容,HowtoreadtheFe-Cphasediagram,20,优选内容,TheIron-IronCarbideDiagram,Thediagramshowsthreehorizontallineswhichindicateisothermalreactions(oncooling/heating):Firsthorizontallineisat1490C,whereperitecticreactiontakesplace:Liquid+austeniteSecondhorizontallineisat1130C,whereeutecticreactiontakesplace:liquidaustenite+cementiteThirdhorizontallineisat723C,whereeutectoidreactiontakesplace:austenitepearlite(mixtureofferrite&cementite),21,优选内容,DeltaregionofFe-Fecarbidediagram,Liquid+austenite,22,优选内容,FerriteregionofFe-FeCarbidediagram,23,优选内容,SimplifiedIron-Carbonphasediagram,austenitepearlite(mixtureofferrite&cementite),24,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,25,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,Inordertounderstandthetransformationprocesses,considerasteeloftheeutectoidcomposition.0.8%carbon,beingslowcooledalonglinex-x.Attheuppertemperatures,onlyausteniteispresent,withthe0.8%carbonbeingdissolvedinsolidsolutionwithintheFCC.Whenthesteelcoolsthrough723C,severalchangesoccursimultaneously.,26,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,TheironwantstochangecrystalstructurefromtheFCCaustenitetotheBCCferrite,buttheferritecanonlycontain0.02%carboninsolidsolution.Theexcesscarbonisrejectedandformsthecarbon-richintermetallicknownascementite.,27,优选内容,Pearliticstructure,Thenetreactionattheeutectoidistheformationofpearliticstructure.Sincethechemicalseparationoccursentirelywithincrystallinesolids,theresultantstructureisafinemixtureofferriteandcementite.,28,优选内容,Schematicpictureoftheformationandgrowthofpearlite,Ferrite,Cementite,Austeniteboundary,29,优选内容,Nucleation&growthofpearlite,30,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,Hypo-eutectoidsteels:Steelshavinglessthan0.8%carbonarecalledhypo-eutectoidsteels(hypomeanslessthan).Considerthecoolingofatypicalhypo-eutectoidalloyalongliney-y.Athightemperaturesthematerialisentirelyaustenite.Uponcoolingitentersaregionwherethestablephasesareferriteandaustenite.Thelow-carbonferritenucleatesandgrows,leavingtheremainingaustenitericherincarbon.,31,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,Hypo-eutectoidsteels-At723C,theremainingaustenitewillhaveassumedtheeutectoidcomposition(0.8%carbon),andfurthercoolingtransformsittopearlite.Theresultingstructure,isamixtureofprimaryorpro-eutectoidferrite(ferritethatformsbeforetheeutectoidreaction)andregionsofpearlite.,32,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,Hyper-eutectoidsteels(hypermeansgreaterthan)arethosethatcontainmorethantheeutectoidamountofCarbon.Whensuchasteelcools,asalonglinez-z,theprocessissimilartothehypo-eutectoidsteel,exceptthattheprimaryorpro-eutectoidphaseisnowcementiteinsteadofferrite.,33,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,Asthecarbon-richphasenucleatesandgrows,theremainingaustenitedecreasesincarboncontent,againreachingtheeutectoidcompositionat723C.Thisaustenitetransformstopearliteuponslowcoolingthroughtheeutectoidtemperature.Theresultingstructureconsistsofprimarycementiteandpearlite.Thecontinuousnetworkofprimarycementitewillcausethematerialtobeextremelybrittle.,34,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,Hypo-eutectoidsteelshowingprimarycementitealonggrainboundariespearlite,35,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,Itshouldbenotedthatthetransitionsasdiscussed,areforequilibriumconditions,asaresultofslowcooling.Uponslowheatingthetransitionswilloccurinthereversemanner.,36,优选内容,TheAustenitetoferrite/cementitetransformationinrelationtoFe-Cdiagram,Whenthealloysarecooledrapidly,entirelydifferentresultsareobtained,sincesufficienttimemaynotbeprovidedforthenormalphasereactionstooccur.Inthesecases,theequilibriumphasediagramisnolongeravalidtoolforengine