Unit-13-Heat-Treatment-of-Metal-机电专业英语-课件

Unit13HeatTreatmentofMetalUnit13HeatTreatmentofMeta1ContentsNewWords&Expressions

Text&TranslationComplexSentenceAnalysisKeytoExercisesContentsNewWords&Expression2NewWords&Expressionsforge[fɔ:dʒ]v.铸造,伪造transformation[͵trænsfə'meiʃən]n.变换，转换，相变eutectoid[ju:'tektɔid]adj.类似共熔体的，共析的austenite['ɔstinait]n.奥氏体pearlite['pə:lait]n.珠光体cementite[si'mentait]n.渗碳体NewWords&Expressionsforge3NewWords&Expressionsmartensitic['mɑ:tən͵zaitik]adj.马氏体的stressrelieving消除应力，低温退火tempering['tempəriŋ]n.回火normalizing['nɔ:məlaiziŋ]n.正火ferrousalloy铁合金still[stil]adj.不动的，静止的 fullannealing完全退火 notably['nəutəbli]adv.显著地,特别是NewWords&Expressionsmarten4NewWords&Expressionsaustenitize['ɔstinitaiz]v.奥氏体化，使成奥氏体denote[di'nəut]v.指示，表示，概述machinability[mə'ʃi:nəbiliti]n.切削加工性，机械加工性能facilitation[fə͵sili'teiʃn]n.容易化，助长，便于in-process['prəuses]adj.(加工、处理)过程中的qualification[͵kwɔlifi'keiʃən]n.资格,条件,限制,限定quenching[kwentʃ]n.淬火NewWords&Expressionsausten5NewWords&Expressionsbrine[brain]n.盐水caustic['kɔ:stik]adj.腐蚀性的,碱性的aqueous['eikwiəs]adj.水的,水成的warp[wɔ:p]n.翘曲，变形fogquenching喷雾淬火interruptedquenching分级淬火selectivequenching局部淬火quench-hardened['kwentʃ͵hɑ:dnd]adj.淬硬的processannealing中间退火，工序间退火NewWords&Expressionsbrine[6Text&TranslationThegenerallyaccepteddefinitionforheattreatingmetalsandmetalalloysis“heatingandcoolingasolidmetaloralloyinawaysoastoobtainspecificconditionsand/orproperties.”Heatingforthesolepurposeofhotworking(asinforgingoperations)isexcludedfromthisdefinition.Likewise，thetypesofheattreatmentthataresometimesusedforproductssuchasglassorplasticsarealsoexcludedfromcoveragebythisdefinition.Text&TranslationThegenerall7Text&Translation1.TransformationCurvesHeattreatmentbasesonthetime—temperature—transformationcurvesorTTTcurves;allthethreeparametersareplottedinasinglediagram.Becauseoftheshapeofthecurves，theyarealsosometimescalledC-curvesorS-curves.Fig.13.1showstheisothermaldecompositiondiagramofT80steel.Text&Translation1.Transforma8Text&TranslationToplotTTTcurves，theparticularsteelisheldatagiventemperatureandthestructureisexaminedatpredeterminedintervalstorecordtheamountoftransformationtakenplace.［1］Itisknownthattheeutectoidsteel(T80)underequilibriumconditionscontains，allausteniteabove723℃,whereasbelow，itispearlite.Toformpearlite，thecarbonatomsshoulddiffusetoformcementite.Thediffusionbeingarateprocess，wouldrequiresufficienttimeforcompletingtransformationofaustenitetopearlite.Fromdifferentsamples，itispossibletonotetheamountofthetransformationtakingplaceatanytemperature.［2］Thesepointsarethenplottedonagraphwithtimeandtemperatureastheaxes.Throughthesepoints，transformationcurvescanbeplottedasshowninFig.13.1foreutectoidsteel.Text&TranslationToplotTTT9Text&TranslationThecurveatextremeleftrepresentsthetimerequiredforthetransformationofaustenitetopearlitetostartatanygiventemperature.Similarly，thecurveatextremerightrepresentsthetimewhichisrequiredforcompletingthetransformation.Thepointsrepresentingpartialtransformationarebetweenthetwocurves.ThestartandfinishofmartensitictransformationarerepresentedbythehorizontallinesMsandMf.Text&TranslationThecurveat10Fig.13-1IsothermalDecompositionDiagramofT80SteelFig.13-1IsothermalDecompos11Text&Translation2.ClassificationofHeatTreatingProcessesInsomeinstances，heattreatmentproceduresareclearcutintermsoftechniqueandapplication，whileinotherinstances，descriptionsorsimpleexplanationsareinsufficientbecausethesametechniquefrequentlymaybeusedtoobtaindifferentobjectives.Forexample，stressrelievingandtemperingareoftenaccomplishedwiththesameequipmentandbyuseofidenticaltimeandtemperaturecycles.Theobjectives，however，aredifferentforthetwoprocesses.Thefollowingdescriptionsoftheprincipalheattreatingprocessesaregenerallyarrangedaccordingtotheirinterrelationships.Text&Translation2.Classifica12Text&Translation1)NormalizingNormalizingmeansheatingaferrousalloytoasuitabletemperature(usually50°Fto100°For28°Cto56°C)aboveitsspecificuppertransformationtemperature.［3］Thisisfollowedbycoolinginstillairtoatleastsometemperaturewellbelowitstransformationtemperaturerange.Forlowcarbonsteels，theresultingstructureandpropertiesarethesameasthoseachievedbyfullannealing；formostferrousalloys，normalizingandannealingaredifferent.Text&Translation1)Normalizin13Text&TranslationNormalizingusuallyisusedasaconditioningtreatment，notablyforrefiningthegrainsofsteelsthathavebeensubjectedtohightemperaturesforforgingorotherhotworkingoperations.Thenormalizingprocessusuallyissucceededbyanotherheattreatingoperationsuchasaustenitizingforhardening，annealing，ortempering.Text&TranslationNormalizing14Text&Translation2)AnnealingAnnealingisagenerictermdenotingaheattreatmentthatconsistsofheatingtoandholdingatasuitabletemperaturefollowedbycoolingatasuitablerate.Itisusedprimarilytosoftenmetallicmaterials，butalsotosimultaneouslyproducedesiredchangesinotherpropertiesorinmicrostructure.Thepurposeofsuchchangesmaybe，butisnotconfinedto，improvementofmachinability，facilitationofcoldwork(knownasinprocessannealing)，improvementofmechanicalorelectricalproperties，ortoincreasedimensionalstability.Whenappliedsolelytorelievestresses，itcommonlyiscalledstressreliefannealing，synonymouswithstressrelieving.Whentheterm“annealing”isappliedtoferrousalloyswithoutqualification，itmeansfullannealing.Thisisachievedbyheatingabovethealloy’stransformationtemperature，thenapplyingacoolingcyclewhichprovidesmaximumsoftness.Thiscyclemayvarywidely，dependingoncompositionandcharacteristicsofthespecificalloy.Text&Translation2)Annealing15Text&Translation3)QuenchingQuenchingistherapidcoolingofasteeloralloyfromtheaustenitizingtemperaturebyimmersingtheworkpieceinaliquidorgaseousmedium.Quenchingmediacommonlyusedincludewater，5%brine，5%causticinanaqueoussolution，oil，polymersolutions，orgas(usuallyairornitrogen).Selectionofaquenchingmediumdependslargelyonthehardenabilityofthematerialandthemassofthematerialbeingtreated(principallysectionthickness).Text&Translation3)Quenching16Text&TranslationThecoolingcapabilitiesoftheabovelistedquenchingmediadiffersalot.Inselectingaquenchingmedium，itisbesttoavoidasolutionthathasmorecoolingpowerthanisneededtoachievetheresults，thusminimizingthepossibilityofcrackingandwarpofthepartsbeingtreated.Modificationsofthetermquenchingincludedirectquenching，fogquenching，hotquenching，interruptedquenching，selectivequenching，sprayquenching，andtimequenching.Text&TranslationThecooling17Text&Translation4)TemperingInheattreatingofferrousalloys，temperingconsistsofreheatingtheaustenitizedandquenchhardenedsteelorirontosomepreselectedtemperaturethatisbelowthelowertransformationtemperature(generallybelow1300°For705°C).Temperingoffersameansofobtainingvariouscombinationsofmechanicalproperties.Temperingtemperaturesusedforhardenedsteelsareoftennohigherthan300°F(150°C).Theterm“tempering”shouldnotbeconfusedwitheitherprocessannealingorstressrelieving.Eventhoughtimeandtemperaturecyclesforthethreeprocessesmaybethesame，theconditionsofthematerialsbeingprocessedandtheobjectivesmaybedifferent.Text&Translation4)Tempering18Text&Translation5)StressrelievingLiketempering，stressrelievingisalwaysdonebyheatingtosometemperaturebelowthelowertransformationtemperatureforsteelsandirons.Fornonferrousmetals，thetemperaturemayvaryfromslightlyaboveroomtemperaturetoseveralhundreddegrees，dependingonthealloyandtheamountofstressreliefthatisdesired.Text&Translation5)Stressrel19Text&TranslationTheprimarypurposeofstressrelievingistorelievestressesthathavebeenimpartedtotheworkpiecefromsuchprocessesasforming，rolling，machiningorwelding.Theusualprocedureistoheatworkpiecestothepreestablishedtemperaturelongenoughtoreducetheresidualstresses(thisisatimeandtemperaturedependentoperation)toanacceptablelevel；thisisfollowedbycoolingatarelativelyslowratetoavoidcreationofnewstresses.Text&TranslationTheprimary20Text&Translation普遍认同的对金属及合金热处理的定义是，以一定的方式加热或和冷却固态金属或合金以达到一定的条件和/或获得某些性能。以热加工(如锻造)为目的的加热，不在此定义之列。同样地，有时用于生产诸如玻璃或塑料制品的热处理也不属于该定义的范畴。Text&Translation普遍认同的对金属及合金热21Text&Translation1.相变曲线热处理的基础分别是时间-温度-相变曲线，即TTT曲线，3个参数都绘制在一个图中。根据曲线的形状特点，分别称为C曲线或S曲线。如图13-1所示为共析钢的等温转变曲线图。Text&Translation1.相变曲线22Text&Translation为了绘制TTT曲线，将特定的钢置于给定温度下，以预先确定的时间间隔检查其结构，记录发生相变的量。我们知道共析钢(C80)在平衡条件下，在723

℃以上时全为奥氏体，而低于此温度，则为珠光体。为了形成珠光体，碳原子将产生扩散形成渗碳体。扩散是一种渐进过程，需要足够的时间完成奥氏体向珠光体的转变。对于不同的样品，可以记录下在任一温度时产生相变的量。然后把这些点绘制在一条以时间和温度为坐标轴的曲线上。通过这些点就可以得到图13-1所示的共析钢的相变曲线。左边的曲线表示任一给定温度下奥氏体开始转变为珠光体所需要的时间。类似地，右边的曲线表示相变完成所需要的时间。两条曲线之间是表示部分相变的点。两条水平线Ms和Mf表示马氏体转变的开始和结束。Text&Translation为了绘制TTT曲线，将23Text&Translation图13-1共析钢的等温转变曲线图Text&Translation图13-1共析钢的等温24Text&Translation2.热处理工艺的分类在某些场合热处理过程可以根据其工艺和应用明确地区分开来。而在另一些场合，因为同样的工艺常常可以用来达到不同的目的，因此对该术语的说明和简单的解释是不够的。例如：消除应力的热处理和回火处理常常使用同样的设备、同样的时间和温度循环来实现，但这两种工艺的目的是不同的。下面对主要热处理工艺的描述大体上是按其相互关系来安排的。Text&Translation2.热处理工艺的分类25Text&Translation1）正火把铁类合金加热到指定的相变温度上限以上(通常50～100F或28～56°C)的合适温度。接下来在不流动的空气中冷却到至少比相变温度低得多的某一温度。对于低碳钢，得到的结构和性能与完全退火相同。而对于大多数铁类合金，正火和退火意义不同。正火一般作为起调节作用的热处理工艺，特别是用于细化在锻造或其他热加工工艺中经受了高温的钢的晶粒。正火处理之后通常还要接着进行淬火、退火或回火等进行奥氏体化。Text&Translation1）正火26Text&Translation2）退火热处理的一个通用术语，指的是加热到一定温度并保温，然后以合适的速度冷却，主要用于降低金属材料的硬度，同时在其他性能或显微组织方面产生一些理想的变化。这种变化的目的是改善其机械加工性、便于冷加工(被称为中间退火)，改善机械或电性能，或增加工件的尺寸稳定性，但也不仅仅局限于此。如果仅仅用于消除应力，就叫做去应力退火，与应力消除(stressrelieving)热处理是同义词。Text&Translation2）退火27Text&Translation当“退火”这个术语用于铁类合金而又无其他限制条件时，指的是完全退火。这种处理是把合金加热到其相变温度以上，再进行循环冷却以使硬度下降最大。冷却过程的变化范围较大，要看具体合金的成分和特性。3）淬火把钢或合金浸没在液体或气体介质中，从奥氏体化温度下快速冷却。常用的淬火介质有水、5%的盐水、5%的碱性水溶液、油、聚合物溶液或气体(常为空气或氮气)。对淬火介质的选择主要取决于材料的淬透性以及被处理的材料的质量(主要是淬火部分的厚度)。Text&Translation当“退火”这个术语用于铁28Text&Translation上面列出的各种淬火介质的冷却能力有很大的区别。在选择淬火介质时，最好避免选择比达到预期效果所需的冷却能力更强的溶液，从而尽量降低处理零件开裂或变形的可能性。淬火包括直接淬火、喷雾淬火、热淬火、分级淬火、局部淬火、喷射淬火和限时淬火。4）回火在铁类合金的热处理中，回火指的是把奥氏体化和淬硬的钢或铁再加热到预先设定的相变温度下限以下的某一温度(通常低于1300F或705°C)。回火提供了获得各种综合机械性能的方法。用于淬硬钢的回火温度通常低于300F(150°C)。不要把回火与中间退火或去应力退火混淆。即使3种处理方法的时间和温度循环可能相同，但是被处理的材料的状态和目的可能是不同的。Text&Translation上面列出的各种淬火介质的29Text&Translation5）去应力退火与回火相似，去应力退火总是把钢和铁加热到相变温度下限以下的某一温度。对于有色金属，这个温度可以是稍高于室温，也可以达到几百度，取决于合金的种类和期望去除的应力的大小。去应力退火的主要目的是消除在模铸、轧制、机加工、焊接等过程中在工件中产生的应力。通常这一过程是把工件加热到预先设定的温度并保持足够长的时间来降低残留的应力(这是一个与时间和温度有关的工序)。接下来，以比较慢的速度冷却以避免产生新的应力。Text&Translation5）去应力退火30ComplexSentenceAnalysis[1]Itisknownthattheeutectoidsteel(T80)underequilibriumconditionscontains，allausteniteabove723℃，whereasbelow，itispearlite．我们知道共析钢(T80)在平衡条件下，在723℃以上时全为奥氏体，而低于此温度，则为珠光体。①that：引导主语从句，itisknownthat译为“我们知道”。②eutectoidsteel：共析钢③below：指低于723℃。whereasbelow句是个省略句，完整的句子为whereasitisbelow723℃。ComplexSentenceAnalysis[1]I31ComplexSentenceAnalysis[2]Thesepointsarethenplottedonagraphwithtimeandtemperatureastheaxes．然后把这些点绘制在一条以时间和温度为坐标轴的曲线上。Axes:轴，此处为坐标轴。ComplexSentenceAnalysis[2]T32ComplexSentenceAnalysis[3]Thisisfollowedbycoolinginstillairtoatleastsometemperaturewellbelowitstransformationtemperaturerange．接下来在不流动的空气中冷却到至少比相变温度低得多的某一温度。①follow：接着，跟着②this：代替上一句话的内容，先heatingaferrousalloy...，接下来，再cooling...ComplexSentenceAnalysis[3]T33KeytoExercisesⅠ.TranslatethefollowingphrasesintoChineseorEnglish.1.金属的热处理2.Transformationcurves3.奥氏体4.pearlite5.渗碳体6.normalizing7.退火8.quenching9.回火10.stressrelievingKeytoExercisesⅠ.Translatet34KeytoExercisesⅡ.MarkthefollowingstatementwithTrue(T)orFalse(F)accordingtothetext.1.T2.F3.T4.T5.TKeytoExercisesⅡ.Markthefo35KeytoExercisesⅢ.Fillintheblankswiththesuitablewordsorphrasesgivenbelow.1.atagiventemperature2.Itisknown3.Toformpearlite4.itispossible5.Throughthesepoints6.SimilarlyKeytoExercisesⅢ.Fillinthe36KeytoExercisesⅣ.TranslatetheChinesepartsgiveninthebracketsintoEnglish.1.coolingatasuitablerate2.inaliquidorgaseousmedium3.Serruptedquenchingselectivequenching，sprayquenching,andtimequenching5.theaustenitizedandquench-hardenedsteelorironKeytoExercisesⅣ.Translateth37Theend!Theend!38Unit13HeatTreatmentofMetalUnit13HeatTreatmentofMeta39ContentsNewWords&Expressions

Text&TranslationComplexSentenceAnalysisKeytoExercisesContentsNewWords&Expression40NewWords&Expressionsforge[fɔ:dʒ]v.铸造,伪造transformation[͵trænsfə'meiʃən]n.变换，转换，相变eutectoid[ju:'tektɔid]adj.类似共熔体的，共析的austenite['ɔstinait]n.奥氏体pearlite['pə:lait]n.珠光体cementite[si'mentait]n.渗碳体NewWords&Expressionsforge41NewWords&Expressionsmartensitic['mɑ:tən͵zaitik]adj.马氏体的stressrelieving消除应力，低温退火tempering['tempəriŋ]n.回火normalizing['nɔ:məlaiziŋ]n.正火ferrousalloy铁合金still[stil]adj.不动的，静止的 fullannealing完全退火 notably['nəutəbli]adv.显著地,特别是NewWords&Expressionsmarten42NewWords&Expressionsaustenitize['ɔstinitaiz]v.奥氏体化，使成奥氏体denote[di'nəut]v.指示，表示，概述machinability[mə'ʃi:nəbiliti]n.切削加工性，机械加工性能facilitation[fə͵sili'teiʃn]n.容易化，助长，便于in-process['prəuses]adj.(加工、处理)过程中的qualification[͵kwɔlifi'keiʃən]n.资格,条件,限制,限定quenching[kwentʃ]n.淬火NewWords&Expressionsausten43NewWords&Expressionsbrine[brain]n.盐水caustic['kɔ:stik]adj.腐蚀性的,碱性的aqueous['eikwiəs]adj.水的,水成的warp[wɔ:p]n.翘曲，变形fogquenching喷雾淬火interruptedquenching分级淬火selectivequenching局部淬火quench-hardened['kwentʃ͵hɑ:dnd]adj.淬硬的processannealing中间退火，工序间退火NewWords&Expressionsbrine[44Text&TranslationThegenerallyaccepteddefinitionforheattreatingmetalsandmetalalloysis“heatingandcoolingasolidmetaloralloyinawaysoastoobtainspecificconditionsand/orproperties.”Heatingforthesolepurposeofhotworking(asinforgingoperations)isexcludedfromthisdefinition.Likewise，thetypesofheattreatmentthataresometimesusedforproductssuchasglassorplasticsarealsoexcludedfromcoveragebythisdefinition.Text&TranslationThegenerall45Text&Translation1.TransformationCurvesHeattreatmentbasesonthetime—temperature—transformationcurvesorTTTcurves;allthethreeparametersareplottedinasinglediagram.Becauseoftheshapeofthecurves，theyarealsosometimescalledC-curvesorS-curves.Fig.13.1showstheisothermaldecompositiondiagramofT80steel.Text&Translation1.Transforma46Text&TranslationToplotTTTcurves，theparticularsteelisheldatagiventemperatureandthestructureisexaminedatpredeterminedintervalstorecordtheamountoftransformationtakenplace.［1］Itisknownthattheeutectoidsteel(T80)underequilibriumconditionscontains，allausteniteabove723℃,whereasbelow，itispearlite.Toformpearlite，thecarbonatomsshoulddiffusetoformcementite.Thediffusionbeingarateprocess，wouldrequiresufficienttimeforcompletingtransformationofaustenitetopearlite.Fromdifferentsamples，itispossibletonotetheamountofthetransformationtakingplaceatanytemperature.［2］Thesepointsarethenplottedonagraphwithtimeandtemperatureastheaxes.Throughthesepoints，transformationcurvescanbeplottedasshowninFig.13.1foreutectoidsteel.Text&TranslationToplotTTT47Text&TranslationThecurveatextremeleftrepresentsthetimerequiredforthetransformationofaustenitetopearlitetostartatanygiventemperature.Similarly，thecurveatextremerightrepresentsthetimewhichisrequiredforcompletingthetransformation.Thepointsrepresentingpartialtransformationarebetweenthetwocurves.ThestartandfinishofmartensitictransformationarerepresentedbythehorizontallinesMsandMf.Text&TranslationThecurveat48Fig.13-1IsothermalDecompositionDiagramofT80SteelFig.13-1IsothermalDecompos49Text&Translation2.ClassificationofHeatTreatingProcessesInsomeinstances，heattreatmentproceduresareclearcutintermsoftechniqueandapplication，whileinotherinstances，descriptionsorsimpleexplanationsareinsufficientbecausethesametechniquefrequentlymaybeusedtoobtaindifferentobjectives.Forexample，stressrelievingandtemperingareoftenaccomplishedwiththesameequipmentandbyuseofidenticaltimeandtemperaturecycles.Theobjectives，however，aredifferentforthetwoprocesses.Thefollowingdescriptionsoftheprincipalheattreatingprocessesaregenerallyarrangedaccordingtotheirinterrelationships.Text&Translation2.Classifica50Text&Translation1)NormalizingNormalizingmeansheatingaferrousalloytoasuitabletemperature(usually50°Fto100°For28°Cto56°C)aboveitsspecificuppertransformationtemperature.［3］Thisisfollowedbycoolinginstillairtoatleastsometemperaturewellbelowitstransformationtemperaturerange.Forlowcarbonsteels，theresultingstructureandpropertiesarethesameasthoseachievedbyfullannealing；formostferrousalloys，normalizingandannealingaredifferent.Text&Translation1)Normalizin51Text&TranslationNormalizingusuallyisusedasaconditioningtreatment，notablyforrefiningthegrainsofsteelsthathavebeensubjectedtohightemperaturesforforgingorotherhotworkingoperations.Thenormalizingprocessusuallyissucceededbyanotherheattreatingoperationsuchasaustenitizingforhardening，annealing，ortempering.Text&TranslationNormalizing52Text&Translation2)AnnealingAnnealingisagenerictermdenotingaheattreatmentthatconsistsofheatingtoandholdingatasuitabletemperaturefollowedbycoolingatasuitablerate.Itisusedprimarilytosoftenmetallicmaterials，butalsotosimultaneouslyproducedesiredchangesinotherpropertiesorinmicrostructure.Thepurposeofsuchchangesmaybe，butisnotconfinedto，improvementofmachinability，facilitationofcoldwork(knownasinprocessannealing)，improvementofmechanicalorelectricalproperties，ortoincreasedimensionalstability.Whenappliedsolelytorelievestresses，itcommonlyiscalledstressreliefannealing，synonymouswithstressrelieving.Whentheterm“annealing”isappliedtoferrousalloyswithoutqualification，itmeansfullannealing.Thisisachievedbyheatingabovethealloy’stransformationtemperature，thenapplyingacoolingcyclewhichprovidesmaximumsoftness.Thiscyclemayvarywidely，dependingoncompositionandcharacteristicsofthespecificalloy.Text&Translation2)Annealing53Text&Translation3)QuenchingQuenchingistherapidcoolingofasteeloralloyfromtheaustenitizingtemperaturebyimmersingtheworkpieceinaliquidorgaseousmedium.Quenchingmediacommonlyusedincludewater，5%brine，5%causticinanaqueoussolution，oil，polymersolutions，orgas(usuallyairornitrogen).Selectionofaquenchingmediumdependslargelyonthehardenabilityofthematerialandthemassofthematerialbeingtreated(principallysectionthickness).Text&Translation3)Quenching54Text&TranslationThecoolingcapabilitiesoftheabovelistedquenchingmediadiffersalot.Inselectingaquenchingmedium，itisbesttoavoidasolutionthathasmorecoolingpowerthanisneededtoachievetheresults，thusminimizingthepossibilityofcrackingandwarpofthepartsbeingtreated.Modificationsofthetermquenchingincludedirectquenching，fogquenching，hotquenching，interruptedquenching，selectivequenching，sprayquenching，andtimequenching.Text&TranslationThecooling55Text&Translation4)TemperingInheattreatingofferrousalloys，temperingconsistsofreheatingtheaustenitizedandquenchhardenedsteelorirontosomepreselectedtemperaturethatisbelowthelowertransformationtemperature(generallybelow1300°For705°C).Temperingoffersameansofobtainingvariouscombinationsofmechanicalproperties.Temperingtemperaturesusedforhardenedsteelsareoftennohigherthan300°F(150°C).Theterm“tempering”shouldnotbeconfusedwitheitherprocessannealingorstressrelieving.Eventhoughtimeandtemperaturecyclesforthethreeprocessesmaybethesame，theconditionsofthematerialsbeingprocessedandtheobjectivesmaybedifferent.Text&Translation4)Tempering56Text&Translation5)StressrelievingLiketempering，stressrelievingisalwaysdonebyheatingtosometemperaturebelowthelowertransformationtemperatureforsteelsandirons.Fornonferrousmetals，thetemperaturemayvaryfromslightlyaboveroomtemperaturetoseveralhundreddegrees，dependingonthealloyandtheamountofstressreliefthatisdesired.Text&Translation5)Stressrel57Text&TranslationTheprimarypurposeofstressrelievingistorelievestressesthathavebeenimpartedtotheworkpiecefromsuchprocessesasforming，rolling，machiningorwelding.Theusualprocedureistoheatworkpiecestothepreestablishedtemperaturelongenoughtoreducetheresidualstresses(thisisatimeandtemperaturedependentoperation)toanacceptablelevel；thisisfollowedbycoolingatarelativelyslowratetoavoidcreationofnewstresses.Text&TranslationTheprimary58Text&Translation普遍认同的对金属及合金热处理的定义是，以一定的方式加热或和冷却固态金属或合金以达到一定的条件和/或获得某些性能。以热加工(如锻造)为目的的加热，不在此定义之列。同样地，有时用于生产诸如玻璃或塑料制品的热处理也不属于该定义的范畴。Text&Translation普遍认同的对金属及合金热59Text&Translation1.相变曲线热处理的基础分别是时间-温度-相变曲线，即TTT曲线，3个参数都绘制在一个图中。根据曲线的形状特点，分别称为C曲线或S曲线。如图13-1所示为共析钢的等温转变曲线图。Text&Translation1.相变曲线60Text&Translation为了绘制TTT曲线，将特定的钢置于给定温度下，以预先确定的时间间隔检查其结构，记录发生相变的量。我们知道共析钢(C80)在平衡条件下，在723

℃以上时全为奥氏体，而低于此温度，则为珠光体。为了形成珠光体，碳原子将产生扩散形成渗碳体。扩散是一种渐进过程，需要足够的时间完成奥氏体向珠光体的转变。对于不同的样品，可以记录下在任一温度时产生相变的量。然后把这些点绘制在一条以时间和温度为坐标轴的曲线上。通过这些点就可以得到图13-1所示的共析钢的相变曲线。左边的曲线表示任一给定温度下奥氏体开始转变为珠光体所需要的时间。类似地，右边的曲线表示相变完成所需要的时间。两条曲线之间是表示部分相变的点。两条水平线Ms和Mf表示马氏体转变的开始和结束。Text&Translation为了绘制TTT曲线，将61Text&Translation图13-1共析钢的等温转变曲线图Text&Translation图13-1共析钢的等温62Text&Translation2.热处理工艺的分类在某些场合热处理过程可以根据其工艺和应用明确地区分开来。而在另一些场合，因为同样的工艺常常可以用来达到不同的目的，因此对该术语的说明和简单的解释是不够的。例如：消除应力的热处理和回火处理常常使用同样的设备、同样的时间和温度循环来实现，但这两种工艺的目的是不同的。下面对主要热处理工艺的描述大体上是按其相互关系来安排的。Text&Translation2.热处理工艺的分类63Text&Translation1）正火把铁类合金加热到指定的相变温度上限以上(通常50～100F或28～56°C)的合适温度。接下来在不流动的空气中冷却到至少比相变温度低得多的某一温度。对于低碳钢，得到的结构和性能与完全退火相同。而对于大多数铁类合金，正火和退火意义不同。正火一般作为起调节作用的热处理工艺，特别是用于细化在锻造或其他热加工工艺中经受了高温的钢的晶粒。正火处理之后通常还要接着进行淬火、退火或回火等进行奥氏体化。Text&Translation1）正火64Text&Translation2）退火热处理的一个通用术语，指的是加热到一定温度并保温，然后以合适的速度冷却，主要用于降低金属材料的硬度，同时在其他性能或显微组织方面产生一些理想的变化。这种变化的目的是改善其机械加工性、便于冷加工(被称为中间退火)，改善机械或电性能，或增加工件的尺寸稳定性，但也不仅仅局限于此。如果仅仅用于消除应力，就叫做去应力退火，与应力消除(stressrelieving)热处理是同义词。Text&Translation2）退火65Text&Translation当“退火”这个术语用于铁类合金而又无其他限制条件时，指的是完全退火。这种处理是把合金加热到其相变温度以上，再进行循环冷却以使硬度下降最大。冷却过程的变化范围较大，要看具体合金的成分