材料成型及控制工程专业英语 HEAT TREATMENT OF STEEL

会计学1材料成型及控制工程专业英语HEATTREATMENTOFSTEELCHAPTER2HEATTREATMENTOFSTEEL热处理在现代机械工程中的作用不可能评价的过高。由热处理而产生的性能改变是特别重要的。-2-Theroleofheattreatmentinmodernmechanicalengineeringcannotbeoverestimated.Thechangesinthepropertiesofmetalsduetoheattreatmentareofextremelygreatsignificance.第1页/共53页CHAPTER2HEATTREATMENTOFSTEEL2.1.1temperatureandtime温度和时间-3-任何热处理的目的都是（通过）将金属加热到一定的温度并(随后)冷却,以使金属组织产生所需变化。Thepurposeofanyheattreatingprocessistoproducethedesiredchangesinthestructureofmetalbyheatingtoaspecifiedtemperatureandbysubsequentcooling.第2页/共53页CHAPTER2HEATTREATMENTOFSTEEL2.1.1温度和时间-4-因此，热处理的主要因素是温度和时间，所以任何热处理工艺都以用温度-时间为坐标轴进行表示。Therefore,themainfactorsactinginheattreatmentaretemperatureandtime,sothatanyprocessofheattreatmentcanberepresentedintemperature-time(t-r)coordinates.第3页/共53页2.1.1temperatureandtime温度和时间热处理工艺主要有以下几个参数：加热温度tmax，既合金加热的最高温度；在加热温度下的保温时间；加热速率和冷却速率。-5-Heattreatmentconditionsarecharacterizedbythefollowingparameters:heatingtemperaturetmax,i.e.themaximumtemperaturetowhichanalloymetalisheated;timeofholdingattheheatingtemperature

;heatingrateandcoolingrate.

第4页/共53页2.1.1temperatureandtime温度和时间如果以不变速率加热或冷却，则温度和时间的关系可以具有不同倾斜角的直线。-6-Ifheating(orcooling)ismadeataconstantrate,thetemperature-timerelationshipwillbedescribedbyastraightlinewitharespective

angleofincline.Respective分别的,各自的第5页/共53页2.1.1temperatureandtime温度和时间如果加热速率（或冷却速率）变化，则实际速率由给定温度确定，更严格的说，是温度对时间的无穷变化：即温度对时间的一阶导数。-7-Withavaryingheating(orcooling)rate.theactualrateshouldbeattributedtothegiventemperature,morestrictly,toaninfinitechangeoftemperatureandtime:thatisthefirstderivativeoftemperatureintime.Infinite无限的东西(如空间、时间),[数]无穷大第6页/共53页2.1.1temperatureandtime温度和时间加热可以是复杂的过程，可以包括几个加热阶段、间断式或阶梯式的加热/冷却，冷却到0℃以下等。任何热处理过程都可以描述成为以温度和时间为坐标轴的曲线。-8-Heattreatmentmaybeacomplexprocess,erruptedorstepwiseheating(cooling),coolingtosubzerotemperatures,etc.Aerrupt－中断stepwise－楼梯式的,逐步的subzero-零度以下的（温度）第7页/共53页2.1.2formationofaustenite-9-根据Fe-C相图，在平衡临界点缓慢加热，珠光体转变为奥氏体。一般条件下，转变会延迟导致guore，即转变温度略高于Fe-C相图中的指定温度。Thetransformationofpearlite

intoaustenitecanonlytakeplaceattheequilibriumcriticalpointonaveryslowheatingasfollowsfromtheFe-Cconstitutionaldiagram.Undercommonconditions,thetransformationisretardedandresultsinoverheating,i.e.occursattemperaturesslightlyhigherthanthoseindicatedintheFe-Cdiagram.Constitutionaldiagram相图(构成的,增强体质的,宪法的）pearlite－珠光体retard延迟,使减速,阻止,妨碍,阻碍第8页/共53页2.1.2formationofaustenite当加热温度高于临界点时，珠光体转变为奥氏体，转变速率依赖于过热的程度。(过热、过冷的概念)-10-Whenoverheatedabovethecriticalpoint,pearlitetransformintoaustenite，

therateoftransformationbeingdependentonthedegreeofoverheating.第9页/共53页2.1.2formationofaustenite各温度下的转变时间（依赖于过热度）表明在较高的温度下相变产生较快（时间短）；加热速度快时，相变在较高温度产生。-11-Thetimeoftransformationatvarioustemperatures(dependingonthedegreeofovereating)shows

thatthetransformationtakesplacefaster(inashortertime)atahighertemperatureandoccursatahighertemperatureonaquickerheating.第10页/共53页2.1.2formationofaustenite例如，780℃加热速度较快时，珠光体完全转变为奥氏体需要2分钟，740℃时则需要8分钟。-12-Forinstance,onquickheatingandholdingat780℃，thepearlitetoaustenitetransformationiscompletedin2minutesandonholdingat740°C,in8minutes.℃

——centigrade第11页/共53页2.1.2formationofaustenite-13-转变结束是以奥氏体形成和珠光体(F+渗碳体)消失为标记的。然而，即使在单个晶粒中奥氏体的也不均匀。Theendofthetransformationischaracterizedbyformationofausteniteandthedisappearanceofpearlite(ferrite+cementite).Thisausteniteishoweverinhomogeneouseveninthevolumeofasinglegrain.第12页/共53页2.1.2formationofaustenite-14-早期形成的片状(或li状)珠光体渗碳体，其含碳量高于片状铁素体，这就是奥氏体（成分）不均匀的原因。lamellae薄片状的,薄层状的Inplacesearlieroccupiedbylamellae(orgrains)ofapearliticcementite,thecontentofcarbonisgreaterthaninplacesofferriticlamellae.Thisiswhytheaustenitejustformedisinhomogeneous.第13页/共53页2.1.2formationofaustenite为了获得均匀的奥氏体，加热温度不仅要超过珠光体转变为奥氏体的终点温度，而且要高于这一温度，并保温一段时间，使奥氏体晶粒内发生完全扩散。-15-Inordertoobtainhomogeneousaustenite,itisessentialonheatingnotonly

topassthroughthepointoftheendofpearlitetoaustenitetransformation,butalso

tooverheatthesteelabovethatpointandtoallowaholdingtimetocompletethediffusionprocessesinausteniticgrains第14页/共53页-16-奥氏体均匀化的速度主要依赖与钢的原始组织，特别是渗碳体的分布及晶粒形状。当渗碳体颗粒细小均匀，总表面积较大时，相转变更快。Therateofhomogenizationofausteniteappreciably

dependsontheoriginalstructureofthesteel,inparticularonthedispersionandparticleshapeofcementite.Thetransformationsdescribedoccurmorequicklywhencementiteparticlesarefineand,therefore,havealargetotalsurfacearea.Particle

粒子,点,极小量,微粒Appreciably1.有一点儿的;可以感到的;2.可观的,值得重视的2.1.2formationofaustenite第15页/共53页2.1.3CoarseningofAusteniteGrains

在珠光体向奥氏体转变开始时，奥氏体首先在铁素体和渗碳体（珠光体的组织组分）之间的晶界处形成。因为晶界非常多因此转变首先形成于大量的细小晶粒。developed

–发达的，引申为“多”。-17-Atthebeginningofpearlitetoaustenitetransformation.Thefirstgrainsofausteniteformattheboundariesbetweentheferriteandcementite–thetwostructuralconstituentsofpearlite.Sincetheseboundariesareverydeveloped,thetransformationstartsfromformationofamultitudeoffinegrains.第16页/共53页CoarseningofAusteniteGrains

因此，奥氏体转变结束时，会形成大量的细小晶粒，它们的尺寸称之为奥氏体初始晶粒度。-18-Therefore,attheendofthetransformationtheaustenitewillbecomposedofagreatmultitudeoffinegrainswhosesizecharacterizeswhatiscalledtheoriginalaustenitegrainsize.第17页/共53页随着加热(保温)温度高于转变温度，将引起奥氏体晶粒的粗化。晶粒粗化的过程是自发的，因为晶粒总面积减少（表面能减少）和高温可以加速转变过程。-19-Furtherheating(orholding)uponthetransformationwillcausecoarseningofausteniticgrains.Theprocessofgraincoarseningisspontaneous,sincethetotalsurfaceareaofgrainsdiminishes(thesurfaceenergydecreases)andahightemperaturecanonlyacceleratetherateofthisprocess.第18页/共53页inthatconnection在那种情况下,如果情况是那样liability、liable有责任的,有义务的,易...的,有...倾向的,inherent固有的,内在的,与生俱来的在那种情况下，就可以形成两种钢：固有细晶粒(钢)和固有粗晶粒(钢)。前者晶粒粗化的倾向比后者小。钢中通过热处理形成的晶粒尺寸称之为实际晶粒度。-20-Inthatconnection,twotypesofsteelsaredistinguished:inherentfinegrainedandinherentcoarsegrained,the

formerbeinglessliabletograincoarseningthanthelatter.Thesizeofgrainsformedinasteelbyheattreatmentiscalledtheactualgrainsize.第19页/共53页因此，区分如下：

(1)原始晶粒度，即珠光体刚转变为奥氏体时奥氏体的晶粒尺寸；

(2)固有晶粒度，即奥氏体粗化的倾向性；

(3)实际晶粒度，也就是在给定条件下的奥氏体实际晶粒尺寸。-21-Thus,adistinctionshouldbemadebetween:(1)originalgrain,i.e.thesizeofausteniticgrainsimmediatelyafterthepearlitetoaustenitetransformation;(2)inherent(natural)grain,i.e.theliabilityofaustenitetograincoarsening;and(3)actualgrain,i.e.thesizeofausteniticgrainsundergivenparticularconditions.第20页/共53页2.1.3CoarseningofAusteniteGrains

-22-奥氏体转变为珠光体时珠光体晶粒的大小决定于奥氏体形成时的晶粒大小。奥氏体仅在加热时长大（冷却时不细化），因为奥氏体区的最高温度和固有晶粒度决定了最终晶粒尺寸。Thesizeofpearliticgrainsatsametemperatureoftheaustenitetopearlitetransformationdependsonthatoftheausteniticgrainsfromwhichtheyhaveformed.Austeniticgrainsgrowonlyduringheating(butarenotrefinedinsubsequentcooling),becauseofwhichthehighesttemperatureasteelisheatedtointheausteniticstateandtheinherentgrainsizeofthatsteeldeterminethefinalgrainsize.第21页/共53页2.1.3CoarseningofAusteniteGrains

-23-钢的性能仅仅由最终晶粒大小而不是固有晶粒大小决定。具有相同等级的两种钢(一是固有粗晶粒，另一是细晶粒)根据不容温度的热处理，将有相同的实际晶粒尺寸，它们的性质也将相同。否则，两种钢的许多性能将不同。Thepropertiesofasteelareaffectedonlybytheactualgrainsizeand

notbytheinherentgrainsize.Iftwosteelsofthesamegrade(oneinherentlycoarsegrained,theotherfinegrained)havethesameactualgrainsizeuponheattreatmentatdifferenttemperatures,theirpropertieswillalsobethesame;ifotherwise,manypropertiesofthetwosteelswillalsobedifferent.第22页/共53页2.1.4DecompositionofAustenite-24-奥氏体向珠光体转变本质是奥氏体分解为近乎纯的铁素体和渗碳体。Theaustenitetopearlitetransformationisessentiallythedecompositionofausteniteintoalmostpureferriteandcementite.第23页/共53页2.1.4decompositionofAustenite-25-在平衡温度时，不发生转变，因为初始奥氏体的自由能等于最终产物珠光体的自由能。Attheequilibriumtemperature,thetransformationisimpossible,sincethefreeenergyoftheoriginalausteniteisequaltothatofthefinalproduct,pearlite.第24页/共53页2.1.4decompositionofAustenite-26-只有珠光体(铁素体和碳化物的混合物)的自由能低于奥氏体，在一定的过冷度下，转变才发生。Thetransformationcanonlystartatacertainundercoolingwhenthefreeenergyoftheferritecarbidemixture(pearlite)islowerthanthatofaustenite.第25页/共53页-27-转变温度越低、过冷度越大，自由能差越大，转变速度越快。Thelowerthetransformationtemperature,thehigherthedegreeofundercoolingandthegreaterthedifferenceinfreeenergiesandthetransformationproceedsatahigherrate.2.1.4DecompositionofAustenite第26页/共53页-28-在珠光体转变中，新相的成分与原始相完全不同，铁素体几乎不含碳，渗碳体含碳6.67％。，inthepearlitetransformation,thenewphasesharplydifferintheircompositionfromtheinitialphase;theyareferritewhichisalmostfreeofcarbon,andcementitewhichcontains6.67percentcarbon.2.1.4DecompositionofAustenite第27页/共53页-29-因此奥氏体转变为珠光体伴随着碳的扩散和重新分布。随着温度的降低，扩散率显著降低，因此，转变需在较高的过冷下，转变会被延迟。Forthisreasontheaustenitetopearlitetransformationisaccompaniedwiththediffusion,redistributionofcarbon.Therateofdiffusionsharplydiminisheswithdecreasingtemperature,therefore,thetransformationshouldberetardedatagreaterundercooling.2.1.4DecompositionofAustenite第28页/共53页-30-因此，可得出一重要结论：过冷（较低的转变温度）对转变速率可以产生两种相反的影响。thus,wehavecometoanimportantconclusionthatundercooling(loweringthetransformationtemperature)mayhavetwooppositeeffectsontherateoftransformation.2.1.4DecompositionofAustenite第29页/共53页-31-一方面，温度较低，过冷较大，使奥氏体和珠光体自由能差较大，因此加速相变，另一方面，它降低了碳扩散的速率，又减慢了相转变。Ononehand,alowertemperature(greaterundercooling)givesagreaterdifferenceinfreeenergyofausteniteandpearlite,thusacceleratingthetransformation;ontheotherhand,itdiminishestherateofcarbondiffusion,andthusslowsdownthetransformation.2.1.4DecompositionofAustenite第30页/共53页-32-整个影响就是：随着过冷度的增加，转变率增加到某一最大值后，随着进一步的过冷而降低.Thecombinedeffectisthattherateoftransformationfirstincreaseasundercoolingisincreasedtoacertainmaximumandthendecreaseswithfurtherundercooling.2.1.4DecompositionofAustenite第31页/共53页-33-在727℃和低于200℃时，转变率为0，因为727℃时自由能差为0，低于200℃时，C的扩散率为0.（更严格的来讲，温度太低，转变难以进行。）at727℃(A1)andbelow200℃,therateoftransformationsiszero,sinceat727℃thefreeenergydifferenceiszeroandbelow200℃therateofcarbondiffusioniszero(morestrictly,toolowforthetransformationtoproceed).2.1.4DecompositionofAustenite第32页/共53页-34-珠光体的形成是珠光体形核和珠光体晶粒长大的过程，这一点首先由I.L.Mirkin在1939年提出，并由R.F.Mehl在1941年加以完善。AshasbeenfirstindicatedbyI.L.Mirkinin1939andthendevelopedbyR.F.Mehlin1941,theformationofpearliteistheprocessofnucleationofpearliteandgrowthofpearliticcrystals.2.1.4DecompositionofAustenite第33页/共53页-35-因此，在不同过冷程度下珠光体的转变速率不同,(这)主要是因为过冷度影响形核率N和晶核长大速率G。在A1和200℃以下，N和G都等于0，并在在150~200℃时过冷度最大.Therefore,thedifferentrateofthepearlitetransformationatvariousdegreesofundercoolingisduetothefactthatundercoolingdifferentlyaffectstherateofnucleationNandtherateofcrystalgrowthG.AttemperatureA1andbelow200℃,bothparametersofcrystallizationNandGareequaltozeroandhaveamaximumatanundercoolingof150~200℃.2.1.4DecompositionofAustenite第34页/共53页-36-如前所述，当条件允许，例如奥氏体过冷到A1点以下，C的扩散速率不为0，则产生形核中心，继而形成晶粒。随时间变化产生的这一过程可用动力学转变曲线表示，该曲线中会显示从转变开始后，随时间变化，珠光体的形成量。Itfollowsfromtheforgoingthatassoonastheconditionsarefavorable,i.e.austeniteisundercolledbelowA1,thediffusionofcarbonisnotzero,centersofcrystallizationappear,whichgiverisetocrystals.Thisprocessoccurswithtimeandcanberepresentedintheformofsocalledkineticcurveoftransformation,whichshowsthequantityofpearlitethathasformedduringthetimeelapsedfromthebeginningofthetransformation.2.1.4DecompositionofAustenite第35页/共53页-37-初始阶段，转变速率非常慢，称之为孕育期。转变进程中，速率加快，当大约有50%的奥氏体转变为珠光体时，转变速率达到最大。然后转变速率减小并停止。Theinitialstageischaracterizedbyaverylowrateoftransformation;thisiswhatiscalledincubationperiod.Therateoftransformationincreaseswithprogressinthetransformation.Itsmaximumapproximatelycorrespondstothemomentwhenroughly50percentofaustenitehastransformedintopearlie.Therateoftransformationthendiminishesandfinallystops.2.1.4DecompositionofAustenite第36页/共53页-38-转变速率依赖于过冷度，过冷度过低和过高都使转变进程变慢，这是由于N、G比较小，前者是由于自由能差过低，后者是因为原子扩散慢，在转变速率最大处，动力学曲线上有峰值，在较短的时间间隔里，转变结束。Therateoftransformationdependsonundercooling.Atlowandhighdegreesofundercoolingthetransformationproceedsslowly,sinceNandGarelow:intheformercase,owingtoalowdifferenceinfreeenergy,andinthelater,duetoalowdiffusionmobilityofatoms.Atthemaximumrateoftransformationthekineticcurveshavesharppeaks,andthetransformationisfinishedinashorttimeinterval.2.1.4DecompositionofAustenite第37页/共53页-39-在高温时（即过冷度小），转变速度慢，孕育期和完全转变的时间较长，在较低的温度转变，及过冷度较大，转变速率变大，转变时间和孕育期较短。Atahightemperature(slightlyundercooling),thetransformationproceedsslowlyandtheincubationperiodandthetimeofthetransformationproperarelong.Atalowertemperatureofthetransformation,i.e.adeeperundercooling,therateoftransformationisgreater,andthetimeoftheincubationperiodandofthetransformationisshorter.2.1.4DecompositionofAustenite第38页/共53页第39页/共53页-41-已经确定了奥氏体想珠光体转变开始的时间（孕育期）和各种过冷度下转变结束的时间，我们可以绘制一幅图，图左边的曲线代表转变开始的时间，即：过冷态下，奥氏体仍然存在的时间，从纵坐标轴到曲线的部分来度量其（奥氏体）的稳定性。Havingdeterminedthetimeofthebeginningofaustenitetopearlitetransformation(incubationperiod)andthetimeoftheendoftransformationatvariousdegreesofundercooling,wecanconstructadiagraminwhichthelefthandcurvedeterminesthetimeofthebeginningofthetransformation,i.e.thetimeduringwhichaustenitestillexistsintheundercoolingstate,andthesectionfromtheaxisofordinatestothecurveisthemeasureofitsstability.2.1.5TTTDiagramorC-Curve

第40页/共53页-42-在温度500~600℃时，这部分区间最短，即：在此温度下转变在最短时间内开始。Thissectionisshortestatatemperatureof500~600℃,i.e.thetransformationbeginsinashortesttimeatthattemperature.2.1.5TTTDiagramorC-Curve

第41页/共53页-43-右边曲线表示在给定过冷度下，完全转变所需的时间，这时在同一温度下（500~600℃）所用时间最短。注意图中的横坐标是对数形式。这样做是为了更方便，因为珠光体形成速率明显不同（在临界点A1点附近为上千秒，在曲线弯曲处只要一两秒。）Therighthand-curveshowsthetimeneededtocompletethetransformationatagivendegreeofundercolling.Thistimeistheshortestatthesametemperature(500~600℃).Notethattheabscissaofthediagramislogarithmic.Thisisdoneformoreconvenience,sincetheratesofformationofpearliteappreciablydiffer(thousandsofsecondsnearthecriticalpointA1andonlyoneortwosecondsatthebendofthecurve).2.1.5TTTDiagramorC-Curve

第42页/共53页-44-图中曲线下的水平线代表无扩散马氏体转变温度，马氏体有不同的转变机制，稍后讨论。Thehorizontallinebelowthecurvesinthediagramdeterminesthetemperatureofthediffusionless

matensitetransformation.Themartensitetransformationoccursbyadifferentmechanismandwillbediscussedlater.2.1.5TTTDiagramorC-Curve

第43页/共53页-45-我们讨论的图通常称为TTT（时间温度转变）图，或者C曲线，这主要因为曲线特殊的形状。奥氏体分解产物的组织和性能取决于转变发生的温度。DiagramsofthetypewediscussedareusuallycalledTTTdiagrams(timetemperaturetransformation),orCcurve,owingtothespecificshapeofthecurves,thestructureandpropertiesoftheproductsofaustenitedecompositiondependsonthetemperatureatwhichthetransformationhastakenplace.2.1.5TTTDiagramorC-Curve

第44页/共53页-46-高温时，即：过冷度小，形成铁素体和渗碳体混合的粗大晶粒，这可以在显微镜下区分。这种组织称为珠光体。Athightemperatures,i.e.lowdegreesofundercooling,acoarsegrainedmixtureofferriteandcementiteisformedwhichiseasilydistinguishedinthe