會(huì)計(jì)學(xué)1材料成型及控制工程專業(yè)英語HEATTREATMENTOFSTEELCHAPTER2HEATTREATMENTOFSTEEL熱處理在現(xiàn)代機(jī)械工程中的作用不可能評(píng)價(jià)的過高。由熱處理而產(chǎn)生的性能改變是特別重要的。-2-Theroleofheattreatmentinmodernmechanicalengineeringcannotbeoverestimated.Thechangesinthepropertiesofmetalsduetoheattreatmentareofextremelygreatsignificance.第1頁/共53頁CHAPTER2HEATTREATMENTOFSTEEL2.1.1temperatureandtime溫度和時(shí)間-3-任何熱處理的目的都是（通過）將金屬加熱到一定的溫度并(隨后)冷卻,以使金屬組織產(chǎn)生所需變化。Thepurposeofanyheattreatingprocessistoproducethedesiredchangesinthestructureofmetalbyheatingtoaspecifiedtemperatureandbysubsequentcooling.第2頁/共53頁CHAPTER2HEATTREATMENTOFSTEEL2.1.1溫度和時(shí)間-4-因此，熱處理的主要因素是溫度和時(shí)間，所以任何熱處理工藝都以用溫度-時(shí)間為坐標(biāo)軸進(jìn)行表示。Therefore,themainfactorsactinginheattreatmentaretemperatureandtime,sothatanyprocessofheattreatmentcanberepresentedintemperature-time(t-r)coordinates.第3頁/共53頁2.1.1temperatureandtime溫度和時(shí)間熱處理工藝主要有以下幾個(gè)參數(shù)：加熱溫度tmax，既合金加熱的最高溫度；在加熱溫度下的保溫時(shí)間；加熱速率和冷卻速率。-5-Heattreatmentconditionsarecharacterizedbythefollowingparameters:heatingtemperaturetmax,i.e.themaximumtemperaturetowhichanalloymetalisheated;timeofholdingattheheatingtemperature

;heatingrateandcoolingrate.

第4頁/共53頁2.1.1temperatureandtime溫度和時(shí)間如果以不變速率加熱或冷卻，則溫度和時(shí)間的關(guān)系可以具有不同傾斜角的直線。-6-Ifheating(orcooling)ismadeataconstantrate,thetemperature-timerelationshipwillbedescribedbyastraightlinewitharespective

angleofincline.Respective分別的,各自的第5頁/共53頁2.1.1temperatureandtime溫度和時(shí)間如果加熱速率（或冷卻速率）變化，則實(shí)際速率由給定溫度確定，更嚴(yán)格的說，是溫度對(duì)時(shí)間的無窮變化：即溫度對(duì)時(shí)間的一階導(dǎo)數(shù)。-7-Withavaryingheating(orcooling)rate.theactualrateshouldbeattributedtothegiventemperature,morestrictly,toaninfinitechangeoftemperatureandtime:thatisthefirstderivativeoftemperatureintime.Infinite無限的東西(如空間、時(shí)間),[數(shù)]無窮大第6頁/共53頁2.1.1temperatureandtime溫度和時(shí)間加熱可以是復(fù)雜的過程，可以包括幾個(gè)加熱階段、間斷式或階梯式的加熱/冷卻，冷卻到0℃以下等。任何熱處理過程都可以描述成為以溫度和時(shí)間為坐標(biāo)軸的曲線。-8-Heattreatmentmaybeacomplexprocess,erruptedorstepwiseheating(cooling),coolingtosubzerotemperatures,etc.Aerrupt－中斷stepwise－樓梯式的,逐步的subzero-零度以下的（溫度）第7頁/共53頁2.1.2formationofaustenite-9-根據(jù)Fe-C相圖，在平衡臨界點(diǎn)緩慢加熱，珠光體轉(zhuǎn)變?yōu)閵W氏體。一般條件下，轉(zhuǎn)變會(huì)延遲導(dǎo)致guore，即轉(zhuǎn)變溫度略高于Fe-C相圖中的指定溫度。Thetransformationofpearlite

intoaustenitecanonlytakeplaceattheequilibriumcriticalpointonaveryslowheatingasfollowsfromtheFe-Cconstitutionaldiagram.Undercommonconditions,thetransformationisretardedandresultsinoverheating,i.e.occursattemperaturesslightlyhigherthanthoseindicatedintheFe-Cdiagram.Constitutionaldiagram相圖(構(gòu)成的,增強(qiáng)體質(zhì)的,憲法的）pearlite－珠光體retard延遲,使減速,阻止,妨礙,阻礙第8頁/共53頁2.1.2formationofaustenite當(dāng)加熱溫度高于臨界點(diǎn)時(shí)，珠光體轉(zhuǎn)變?yōu)閵W氏體，轉(zhuǎn)變速率依賴于過熱的程度。(過熱、過冷的概念)-10-Whenoverheatedabovethecriticalpoint,pearlitetransformintoaustenite，

therateoftransformationbeingdependentonthedegreeofoverheating.第9頁/共53頁2.1.2formationofaustenite各溫度下的轉(zhuǎn)變時(shí)間（依賴于過熱度）表明在較高的溫度下相變產(chǎn)生較快（時(shí)間短）；加熱速度快時(shí)，相變在較高溫度產(chǎn)生。-11-Thetimeoftransformationatvarioustemperatures(dependingonthedegreeofovereating)shows

thatthetransformationtakesplacefaster(inashortertime)atahighertemperatureandoccursatahighertemperatureonaquickerheating.第10頁/共53頁2.1.2formationofaustenite例如，780℃加熱速度較快時(shí)，珠光體完全轉(zhuǎn)變?yōu)閵W氏體需要2分鐘，740℃時(shí)則需要8分鐘。-12-Forinstance,onquickheatingandholdingat780℃，thepearlitetoaustenitetransformationiscompletedin2minutesandonholdingat740°C,in8minutes.℃

——centigrade第11頁/共53頁2.1.2formationofaustenite-13-轉(zhuǎn)變結(jié)束是以奧氏體形成和珠光體(F+滲碳體)消失為標(biāo)記的。然而，即使在單個(gè)晶粒中奧氏體的也不均勻。Theendofthetransformationischaracterizedbyformationofausteniteandthedisappearanceofpearlite(ferrite+cementite).Thisausteniteishoweverinhomogeneouseveninthevolumeofasinglegrain.第12頁/共53頁2.1.2formationofaustenite-14-早期形成的片狀(或li狀)珠光體滲碳體，其含碳量高于片狀鐵素體，這就是奧氏體（成分）不均勻的原因。lamellae薄片狀的,薄層狀的Inplacesearlieroccupiedbylamellae(orgrains)ofapearliticcementite,thecontentofcarbonisgreaterthaninplacesofferriticlamellae.Thisiswhytheaustenitejustformedisinhomogeneous.第13頁/共53頁2.1.2formationofaustenite為了獲得均勻的奧氏體，加熱溫度不僅要超過珠光體轉(zhuǎn)變?yōu)閵W氏體的終點(diǎn)溫度，而且要高于這一溫度，并保溫一段時(shí)間，使奧氏體晶粒內(nèi)發(fā)生完全擴(kuò)散。-15-Inordertoobtainhomogeneousaustenite,itisessentialonheatingnotonly

topassthroughthepointoftheendofpearlitetoaustenitetransformation,butalso

tooverheatthesteelabovethatpointandtoallowaholdingtimetocompletethediffusionprocessesinausteniticgrains第14頁/共53頁-16-奧氏體均勻化的速度主要依賴與鋼的原始組織，特別是滲碳體的分布及晶粒形狀。當(dāng)滲碳體顆粒細(xì)小均勻，總表面積較大時(shí)，相轉(zhuǎn)變更快。Therateofhomogenizationofausteniteappreciably

dependsontheoriginalstructureofthesteel,inparticularonthedispersionandparticleshapeofcementite.Thetransformationsdescribedoccurmorequicklywhencementiteparticlesarefineand,therefore,havealargetotalsurfacearea.Particle

粒子,點(diǎn),極小量,微粒Appreciably1.有一點(diǎn)兒的;可以感到的;2.可觀的,值得重視的2.1.2formationofaustenite第15頁/共53頁2.1.3CoarseningofAusteniteGrains

在珠光體向奧氏體轉(zhuǎn)變開始時(shí)，奧氏體首先在鐵素體和滲碳體（珠光體的組織組分）之間的晶界處形成。因?yàn)榫Ы绶浅６嘁虼宿D(zhuǎn)變首先形成于大量的細(xì)小晶粒。developed

–發(fā)達(dá)的，引申為“多”。-17-Atthebeginningofpearlitetoaustenitetransformation.Thefirstgrainsofausteniteformattheboundariesbetweentheferriteandcementite–thetwostructuralconstituentsofpearlite.Sincetheseboundariesareverydeveloped,thetransformationstartsfromformationofamultitudeoffinegrains.第16頁/共53頁CoarseningofAusteniteGrains

因此，奧氏體轉(zhuǎn)變結(jié)束時(shí)，會(huì)形成大量的細(xì)小晶粒，它們的尺寸稱之為奧氏體初始晶粒度。-18-Therefore,attheendofthetransformationtheaustenitewillbecomposedofagreatmultitudeoffinegrainswhosesizecharacterizeswhatiscalledtheoriginalaustenitegrainsize.第17頁/共53頁隨著加熱(保溫)溫度高于轉(zhuǎn)變溫度，將引起奧氏體晶粒的粗化。晶粒粗化的過程是自發(fā)的，因?yàn)榫Я？偯娣e減少（表面能減少）和高溫可以加速轉(zhuǎn)變過程。-19-Furtherheating(orholding)uponthetransformationwillcausecoarseningofausteniticgrains.Theprocessofgraincoarseningisspontaneous,sincethetotalsurfaceareaofgrainsdiminishes(thesurfaceenergydecreases)andahightemperaturecanonlyacceleratetherateofthisprocess.第18頁/共53頁inthatconnection在那種情況下,如果情況是那樣liability、liable有責(zé)任的,有義務(wù)的,易...的,有...傾向的,inherent固有的,內(nèi)在的,與生俱來的在那種情況下，就可以形成兩種鋼：固有細(xì)晶粒(鋼)和固有粗晶粒(鋼)。前者晶粒粗化的傾向比后者小。鋼中通過熱處理形成的晶粒尺寸稱之為實(shí)際晶粒度。-20-Inthatconnection,twotypesofsteelsaredistinguished:inherentfinegrainedandinherentcoarsegrained,the

formerbeinglessliabletograincoarseningthanthelatter.Thesizeofgrainsformedinasteelbyheattreatmentiscalledtheactualgrainsize.第19頁/共53頁因此，區(qū)分如下：

(1)原始晶粒度，即珠光體剛轉(zhuǎn)變?yōu)閵W氏體時(shí)奧氏體的晶粒尺寸；

(2)固有晶粒度，即奧氏體粗化的傾向性；

(3)實(shí)際晶粒度，也就是在給定條件下的奧氏體實(shí)際晶粒尺寸。-21-Thus,adistinctionshouldbemadebetween:(1)originalgrain,i.e.thesizeofausteniticgrainsimmediatelyafterthepearlitetoaustenitetransformation;(2)inherent(natural)grain,i.e.theliabilityofaustenitetograincoarsening;and(3)actualgrain,i.e.thesizeofausteniticgrainsundergivenparticularconditions.第20頁/共53頁2.1.3CoarseningofAusteniteGrains

-22-奧氏體轉(zhuǎn)變?yōu)橹楣怏w時(shí)珠光體晶粒的大小決定于奧氏體形成時(shí)的晶粒大小。奧氏體僅在加熱時(shí)長大（冷卻時(shí)不細(xì)化），因?yàn)閵W氏體區(qū)的最高溫度和固有晶粒度決定了最終晶粒尺寸。Thesizeofpearliticgrainsatsametemperatureoftheaustenitetopearlitetransformationdependsonthatoftheausteniticgrainsfromwhichtheyhaveformed.Austeniticgrainsgrowonlyduringheating(butarenotrefinedinsubsequentcooling),becauseofwhichthehighesttemperatureasteelisheatedtointheausteniticstateandtheinherentgrainsizeofthatsteeldeterminethefinalgrainsize.第21頁/共53頁2.1.3CoarseningofAusteniteGrains

-23-鋼的性能僅僅由最終晶粒大小而不是固有晶粒大小決定。具有相同等級(jí)的兩種鋼(一是固有粗晶粒，另一是細(xì)晶粒)根據(jù)不容溫度的熱處理，將有相同的實(shí)際晶粒尺寸，它們的性質(zhì)也將相同。否則，兩種鋼的許多性能將不同。Thepropertiesofasteelareaffectedonlybytheactualgrainsizeand

notbytheinherentgrainsize.Iftwosteelsofthesamegrade(oneinherentlycoarsegrained,theotherfinegrained)havethesameactualgrainsizeuponheattreatmentatdifferenttemperatures,theirpropertieswillalsobethesame;ifotherwise,manypropertiesofthetwosteelswillalsobedifferent.第22頁/共53頁2.1.4DecompositionofAustenite-24-奧氏體向珠光體轉(zhuǎn)變本質(zhì)是奧氏體分解為近乎純的鐵素體和滲碳體。Theaustenitetopearlitetransformationisessentiallythedecompositionofausteniteintoalmostpureferriteandcementite.第23頁/共53頁2.1.4decompositionofAustenite-25-在平衡溫度時(shí)，不發(fā)生轉(zhuǎn)變，因?yàn)槌跏紛W氏體的自由能等于最終產(chǎn)物珠光體的自由能。Attheequilibriumtemperature,thetransformationisimpossible,sincethefreeenergyoftheoriginalausteniteisequaltothatofthefinalproduct,pearlite.第24頁/共53頁2.1.4decompositionofAustenite-26-只有珠光體(鐵素體和碳化物的混合物)的自由能低于奧氏體，在一定的過冷度下，轉(zhuǎn)變才發(fā)生。Thetransformationcanonlystartatacertainundercoolingwhenthefreeenergyoftheferritecarbidemixture(pearlite)islowerthanthatofaustenite.第25頁/共53頁-27-轉(zhuǎn)變溫度越低、過冷度越大，自由能差越大，轉(zhuǎn)變速度越快。Thelowerthetransformationtemperature,thehigherthedegreeofundercoolingandthegreaterthedifferenceinfreeenergiesandthetransformationproceedsatahigherrate.2.1.4DecompositionofAustenite第26頁/共53頁-28-在珠光體轉(zhuǎn)變中，新相的成分與原始相完全不同，鐵素體幾乎不含碳，滲碳體含碳6.67％。，inthepearlitetransformation,thenewphasesharplydifferintheircompositionfromtheinitialphase;theyareferritewhichisalmostfreeofcarbon,andcementitewhichcontains6.67percentcarbon.2.1.4DecompositionofAustenite第27頁/共53頁-29-因此奧氏體轉(zhuǎn)變?yōu)橹楣怏w伴隨著碳的擴(kuò)散和重新分布。隨著溫度的降低，擴(kuò)散率顯著降低，因此，轉(zhuǎn)變需在較高的過冷下，轉(zhuǎn)變會(huì)被延遲。Forthisreasontheaustenitetopearlitetransformationisaccompaniedwiththediffusion,redistributionofcarbon.Therateofdiffusionsharplydiminisheswithdecreasingtemperature,therefore,thetransformationshouldberetardedatagreaterundercooling.2.1.4DecompositionofAustenite第28頁/共53頁-30-因此，可得出一重要結(jié)論：過冷（較低的轉(zhuǎn)變溫度）對(duì)轉(zhuǎn)變速率可以產(chǎn)生兩種相反的影響。thus,wehavecometoanimportantconclusionthatundercooling(loweringthetransformationtemperature)mayhavetwooppositeeffectsontherateoftransformation.2.1.4DecompositionofAustenite第29頁/共53頁-31-一方面，溫度較低，過冷較大，使奧氏體和珠光體自由能差較大，因此加速相變，另一方面，它降低了碳擴(kuò)散的速率，又減慢了相轉(zhuǎn)變。Ononehand,alowertemperature(greaterundercooling)givesagreaterdifferenceinfreeenergyofausteniteandpearlite,thusacceleratingthetransformation;ontheotherhand,itdiminishestherateofcarbondiffusion,andthusslowsdownthetransformation.2.1.4DecompositionofAustenite第30頁/共53頁-32-整個(gè)影響就是：隨著過冷度的增加，轉(zhuǎn)變率增加到某一最大值后，隨著進(jìn)一步的過冷而降低.Thecombinedeffectisthattherateoftransformationfirstincreaseasundercoolingisincreasedtoacertainmaximumandthendecreaseswithfurtherundercooling.2.1.4DecompositionofAustenite第31頁/共53頁-33-在727℃和低于200℃時(shí)，轉(zhuǎn)變率為0，因?yàn)?27℃時(shí)自由能差為0，低于200℃時(shí)，C的擴(kuò)散率為0.（更嚴(yán)格的來講，溫度太低，轉(zhuǎn)變難以進(jìn)行。）at727℃(A1)andbelow200℃,therateoftransformationsiszero,sinceat727℃thefreeenergydifferenceiszeroandbelow200℃therateofcarbondiffusioniszero(morestrictly,toolowforthetransformationtoproceed).2.1.4DecompositionofAustenite第32頁/共53頁-34-珠光體的形成是珠光體形核和珠光體晶粒長大的過程，這一點(diǎn)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頁/共53頁-35-因此，在不同過冷程度下珠光體的轉(zhuǎn)變速率不同,(這)主要是因?yàn)檫^冷度影響形核率N和晶核長大速率G。在A1和200℃以下，N和G都等于0，并在在150~200℃時(shí)過冷度最大.Therefore,thedifferentrateofthepearlitetransformationatvariousdegreesofundercoolingisduetothefactthatundercoolingdifferentlyaffectstherateofnucleationNandtherateofcrystalgrowthG.AttemperatureA1andbelow200℃,bothparametersofcrystallizationNandGareequaltozeroandhaveamaximumatanundercoolingof150~200℃.2.1.4DecompositionofAustenite第34頁/共53頁-36-如前所述，當(dāng)條件允許，例如奧氏體過冷到A1點(diǎn)以下，C的擴(kuò)散速率不為0，則產(chǎn)生形核中心，繼而形成晶粒。隨時(shí)間變化產(chǎn)生的這一過程可用動(dòng)力學(xué)轉(zhuǎn)變曲線表示，該曲線中會(huì)顯示從轉(zhuǎn)變開始后，隨時(shí)間變化，珠光體的形成量。Itfollowsfromtheforgoingthatassoonastheconditionsarefavorable,i.e.austeniteisundercolledbelowA1,thediffusionofcarbonisnotzero,centersofcrystallizationappear,whichgiverisetocrystals.Thisprocessoccurswithtimeandcanberepresentedintheformofsocalledkineticcurveoftransformation,whichshowsthequantityofpearlitethathasformedduringthetimeelapsedfromthebeginningofthetransformation.2.1.4DecompositionofAustenite第35頁/共53頁-37-初始階段，轉(zhuǎn)變速率非常慢，稱之為孕育期。轉(zhuǎn)變進(jìn)程中，速率加快，當(dāng)大約有50%的奧氏體轉(zhuǎn)變?yōu)橹楣怏w時(shí)，轉(zhuǎn)變速率達(dá)到最大。然后轉(zhuǎn)變速率減小并停止。Theinitialstageischaracterizedbyaverylowrateoftransformation;thisiswhatiscalledincubationperiod.Therateoftransformationincreaseswithprogressinthetransformation.Itsmaximumapproximatelycorrespondstothemomentwhenroughly50percentofaustenitehastransformedintopearlie.Therateoftransformationthendiminishesandfinallystops.2.1.4DecompositionofAustenite第36頁/共53頁-38-轉(zhuǎn)變速率依賴于過冷度，過冷度過低和過高都使轉(zhuǎn)變進(jìn)程變慢，這是由于N、G比較小，前者是由于自由能差過低，后者是因?yàn)樵訑U(kuò)散慢，在轉(zhuǎn)變速率最大處，動(dòng)力學(xué)曲線上有峰值，在較短的時(shí)間間隔里，轉(zhuǎn)變結(jié)束。Therateoftransformationdependsonundercooling.Atlowandhighdegreesofundercoolingthetransformationproceedsslowly,sinceNandGarelow:intheformercase,owingtoalowdifferenceinfreeenergy,andinthelater,duetoalowdiffusionmobilityofatoms.Atthemaximumrateoftransformationthekineticcurveshavesharppeaks,andthetransformationisfinishedinashorttimeinterval.2.1.4DecompositionofAustenite第37頁/共53頁-39-在高溫時(shí)（即過冷度?。D(zhuǎn)變速度慢，孕育期和完全轉(zhuǎn)變的時(shí)間較長，在較低的溫度轉(zhuǎn)變，及過冷度較大，轉(zhuǎn)變速率變大，轉(zhuǎn)變時(shí)間和孕育期較短。Atahightemperature(slightlyundercooling),thetransformationproceedsslowlyandtheincubationperiodandthetimeofthetransformationproperarelong.Atalowertemperatureofthetransformation,i.e.adeeperundercooling,therateoftransformationisgreater,andthetimeoftheincubationperiodandofthetransformationisshorter.2.1.4DecompositionofAustenite第38頁/共53頁第39頁/共53頁-41-已經(jīng)確定了奧氏體想珠光體轉(zhuǎn)變開始的時(shí)間（孕育期）和各種過冷度下轉(zhuǎn)變結(jié)束的時(shí)間，我們可以繪制一幅圖，圖左邊的曲線代表轉(zhuǎn)變開始的時(shí)間，即：過冷態(tài)下，奧氏體仍然存在的時(shí)間，從縱坐標(biāo)軸到曲線的部分來度量其（奧氏體）的穩(wěn)定性。Havingdeterminedthetimeofthebeginningofaustenitetopearlitetransformation(incubationperiod)andthetimeoftheendoftransformationatvariousdegreesofundercooling,wecanconstructadiagraminwhichthelefthandcurvedeterminesthetimeofthebeginningofthetransformation,i.e.thetimeduringwhichaustenitestillexistsintheundercoolingstate,andthesectionfromtheaxisofordinatestothecurveisthemeasureofitsstability.2.1.5TTTDiagramorC-Curve

第40頁/共53頁-42-在溫度500~600℃時(shí)，這部分區(qū)間最短，即：在此溫度下轉(zhuǎn)變在最短時(shí)間內(nèi)開始。Thissectionisshortestatatemperatureof500~600℃,i.e.thetransformationbeginsinashortesttimeatthattemperature.2.1.5TTTDiagramorC-Curve

第41頁/共53頁-43-右邊曲線表示在給定過冷度下，完全轉(zhuǎn)變所需的時(shí)間，這時(shí)在同一溫度下（500~600℃）所用時(shí)間最短。注意圖中的橫坐標(biāo)是對(duì)數(shù)形式。這樣做是為了更方便，因?yàn)橹楣怏w形成速率明顯不同（在臨界點(diǎn)A1點(diǎn)附近為上千秒，在曲線彎曲處只要一兩秒。）Therighthand-curveshowsthetimeneededtocompletethetransformationatagivendegreeofundercolling.Thistimeistheshortestatthesametemperature(500~600℃).Notethattheabscissaofthediagramislogarithmic.Thisisdoneformoreconvenience,sincetheratesofformationofpearliteappreciablydiffer(thousandsofsecondsnearthecriticalpointA1andonlyoneortwosecondsatthebendofthecurve).2.1.5TTTDiagramorC-Curve

第42頁/共53頁-44-圖中曲線下的水平線代表無擴(kuò)散馬氏體轉(zhuǎn)變溫度，馬氏體有不同的轉(zhuǎn)變機(jī)制，稍后討論。Thehorizontallinebelowthecurvesinthediagramdeterminesthetemperatureofthediffusionless

matensitetransformation.Themartensitetransformationoccursbyadifferentmechanismandwillbediscussedlater.2.1.5TTTDiagramorC-Curve

第43頁/共53頁-45-我們討論的圖通常稱為TTT（時(shí)間溫度轉(zhuǎn)變）圖，或者C曲線，這主要因?yàn)榍€特殊的形狀。奧氏體分解產(chǎn)物的組織和性能取決于轉(zhuǎn)變發(fā)生的溫度。DiagramsofthetypewediscussedareusuallycalledTTTdiagrams(timetemperaturetransformation),orCcurve,owingtothespecificshapeofthecurves,thestructureandpropertiesoftheproductsofaustenitedecompositiondependsonthetemperatureatwhichthetransformationhastakenplace.2.1.5TTTDiagramorC-Curve

第44頁/共53頁-46-高溫時(shí)，即：過冷度小，形成鐵素體和滲碳體混合的粗大晶粒，這可以在顯微鏡下區(qū)分。這種組織稱為珠光體。Athightemperatures,i.e.lowdegreesofundercooling,acoarsegrainedmixtureofferriteandcementiteisformedwhichiseasilydistinguishedinthe