ch07-应变硬化与退火-E-2

1TheScienceandEngineeringofMaterials,4thed2003

DonaldR.Askeland–PradeepP.PhuléChapter7–StrainHardeningandAnnealing应变硬化(加工硬化)与退火2IntroductiontoChapter1Thetetrahedronofmaterialsscienceandengineering

材料科学与工程四面体3Reviewofknowledge知识回顾Chapter1–IntroductiontoMaterialsScienceandEngineering

绪论Chapter2–AtomicStructure原子结构Chapter3–AtomicandIonicArrangements

原子和离子的排列Chapter4–ImperfectionsintheAtomicandIonicArrangements原子和离子排列中的缺陷Chapter5–AtomandIonMovementsinMaterials

材料中原子和离子的运动Chapter6–MechanicalPropertiesandBehavior

机械性质与行为4

ObjectivesofChapter7第七章目标Tolearnhowthestrengthofmetalsandalloysisinfluencedbymechanicalprocessingandheattreatments.学习机械加工和热处理如何影响金属和合金的强度。Tolearnhowtoenhancethestrengthofmetalsandalloysusingcoldworking.学习如何利用冷加工提高金属和合金的强度Tolearnhowtoenhanceductilityusingannealingheattreatment.学习如何利用退火提高展延性5ChapterOutline本章概要7.1RelationshipofColdWorkingtotheStress-StrainCurve冷加工与应力-应变曲线的关联7.2

Strain-HardeningMechanisms应变硬化的机理7.3PropertiesversusPercentColdWork（%CW）

性质与%CW7.4Microstructure,TextureStrengthening,andResidualStresses微观结构，织构强化，残余应力7.5CharacteristicsofColdWorking冷加工的特性7.6TheThreeStagesofAnnealing退火的三个阶段7.7ControlofAnnealing退火的控制7.8AnnealingandMaterialsProcessing退火和材料处理7.9HotWorking热加工7.10SuperplasticForming(SPF)超塑性成型6

Section7.1RelationshipofColdWorkingtotheStress-StrainCurve冷加工与应力-应变曲线的关联

Strainhardening应变硬化Strainhardeningexponent(n)

应变硬化指数（n）7应变硬化Strainhardening金属材料在再结晶温度以下塑性变形时强度和硬度升高，而塑性和韧性降低的现象。又称冷作硬化。产生原因是，金属在塑性变形时，晶粒发生滑移，出现位错的缠结，使晶粒拉长、破碎和纤维化，金属内部产生了残余应力等。加工硬化的程度通常用加工后与加工前表面层显微硬度的比值和硬化层深度来表示。

加工硬化给金属件的进一步加工带来困难。如在冷轧钢板的过程中会愈轧愈硬以致轧不动，因而需在加工过程中安排中间退火，通过加热消除其加工硬化。又如在切削加工中使工件表层脆而硬，从而加速刀具磨损、增大切削力等。但有利的一面是，它可提高金属的强度、硬度和耐磨性，特别是对于那些不能以热处理方法提高强度的纯金属和某些合金尤为重要。如冷拉高强度钢丝和冷卷弹簧等，就是利用冷加工变形来提高其强度和弹性极限。又如坦克和拖拉机的履带、破碎机的颚板以及铁路的道岔等也是利用加工硬化来提高其硬度和耐磨性的。

8Figure7.2Manufacturingprocessesthatmakeuseofcoldworkingaswellashotworking.Commonmetalworkingmethods冷加工及热加工过程。普通的金属加工方式。Forging锻造Extruding挤压Drawing拉拔Stamping冲压Rolling轧制9Strainhardeningexponent(n)应变硬化指数（n）在金属材料拉伸真应力应变曲线上的均匀塑性变形阶段关系式：σ

=kεn

（σ：真应力，

ε：真应变）

应变硬化指数n反映了金属材料抵抗继续塑性变形的能力，是表征金属材料应变硬化的性能指标。

在极限情况下，n＝1，表示材料为完全理想的弹性体，σ与ε

成正比关系；

n＝0时，σ＝k＝常数，表示材料没有应变硬化能力，例如室温下产生再结晶的软金属及已受强烈应变硬化的材料。大多数金属的n值在0.1~0.5之间。10©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.3Thetruestress-truestraincurvesformetalswithlargeandsmallstrain-hardeningexponents.Largerdegreesofstrengtheningareobtainedforagivenstrainforthemetalwiththelargern具有大的和小的应变硬化指数（n）的金属的真应力-应变曲线，当应变给定时，具有较大n的金属的应变硬化程度更大。lnσ=lnK+nlnε11典型金属和合金的应变硬化指数和强度系数磅力/英寸2(psi)=psi=磅力/英寸2钛钼奥氏体不锈钢淬火和回火中碳钢退火合金钢12Section7.2Strain-HardeningMechanisms应变硬化的机理

Frank-Readsource-Apinneddislocationthat,underanappliedstress,producesadditionaldislocations.Thismechanismisatleastpartlyresponsibleforstrainhardening.弗兰克-瑞德源–一个被钉住的位错，在外加应力的作用下，引起额外的位错。这一机制至少是引起应变硬化的部分原因。Thermoplastics-Aclassofpolymersthatconsistoflarge,longspaghetti-likemoleculesthatareintertwined(e.g.,polyethylene,nylon,PET,etc.).

热塑性塑料

–一类由长链大分子相互缠绕组成的聚合物（例如，聚乙烯，尼龙，聚对苯二甲酸乙二酯等。）13Figure7.5TheFrank-Readsourcecangeneratedislocations.(a)Adislocationispinnedatitsendsbylatticedefects.(b)Asthedislocationcontinuestomove,thedislocationbows,eventuallybendingbackonitself.(c)finallythedislocationloopforms,and(d)anewdislocationiscreated.(e)ElectronmicrographofaFrank-Readsource(330,000).弗兰克-瑞德源能产生位错。(a)一个位错被它两端的晶格缺陷固定。(b)当位错连续运动，该位错变成弓形，最终折回。(c)最后该位错成环形。(d)形成新的位错。(e)弗兰克-瑞德源的电镜照片（330000倍）14©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.6Inanundeformedthermoplasticpolymertensilebar,(a)thepolymerchainsarerandomlyoriented.(b)Whenastressisapplied,aneckdevelopsaschainsbecomealignedlocally.Theneckcontinuestogrowuntilthechainsintheentiregagelengthhavealigned.(c)Thestrengthofthepolymerisincreased在一个未变形的热塑性塑料拉力试棒中，(a)聚合物分子链是随机取向的。(b)当施加应力后，因分子链局部定向排列从而形成细颈。细颈增长直到所有分子链定向排列。(c)聚合物的强度被提高。15Section7.3PropertiesversusPercentColdWork性质与%CW

percent

coldwork的定义是冷加工前初始横截面积与冷加工后最终横截面积的变化百分比，其中包含多个中间过程对结果没有影响。因此总的percent

coldwork实际上是:%CW=[(t0-tf)/t0]X100%16Section7.3PropertiesversusPercentColdWork性质与%CW

©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.7Theeffectofcoldworkonthemechanicalpropertiesofcopper冷加工对铜的机械性质的影响伸长率屈服强度抗张强度17Example7.1ColdWorkingaCopperPlate冷加工铜板

A1-cm-thickcopperplateiscold-reducedto0.50cm,andlaterfurtherreducedto0.16cm.Determinethetotalpercentcoldworkandthetensilestrengthofthe0.16-cmplate.(SeeFigure7.8.)

一块厚度1cm的铜板，被冷加工至0.50cm厚，然后进一步冷加工至0.16cm厚。确定0.16cm厚的板材总的%CW和拉伸强度。18©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.8

Diagramshowingtherollingofa1-cmplate(forExample7.1)轧1cm板的示意图19Example7.1SOLUTION20Example7.2DesignofaColdWorkingProcess设计冷加工工艺

Designamanufacturingprocesstoproducea0.1-cm-thickcopperplatehavingatleast65,000psitensilestrength,60,000psiyieldstrength,and5%elongation.设计一个制造工艺生产拉伸强度不低于65,000psi(磅力/英寸2)，屈服强度不低于60,000psi以及断裂伸长不低于5%的0.1cm厚度的铜板。Example7.2SOLUTIONToproducetheplate,acold-rollingprocesswouldbeappropriate.TheoriginalthicknessofthecopperplatepriortorollingcanbecalculatedfromEquation7-4.Becausethereisarangeofallowablecoldwork—between40%and45%—thereisarangeofinitialplatethicknesses:要生产这种板材，冷轧工艺是适合的。冷轧之前铜板的初始厚度可通过%CW计算。因为允许的%CW在40%~45%范围内（参见图7-7），初始板材厚度范围为：21Example7.2SOLUTION(Continued)Toproducethe0.1-cmcopperplate,webeginwitha0.167-to0.182-cmcopperplateinthesoftestpossiblecondition,thencoldrolltheplate40%to45%toachievethe0.1cmthickness.为生产0.1-cm的铜板，我们用尽可能软的0.167至0.182cm的铜板，冷轧至%CW为40%~45%得到厚度为0.1cm的板材。22Section7.4Microstructure,TextureStrengthening,andResidualStresses微观结构，织构强化，残余应力

Fibertexture,Sheettexture纤维状构造，薄片状构造Polefigureanalysis,Orientationmicroscopy极图分析,取向显微术Residualstresses,Stress-reliefanneal残余应力，消除应力退火Annealingglass,Temperedglass玻璃退火，钢化玻璃23Figure7.9Thefibrousgrainstructureofalowcarbonsteelproducedbycoldworking:(a)10%coldwork,(b)30%coldwork,(c)60%coldwork,and(d)90%coldwork(250).冷加工得到的低碳钢纤维状晶粒结构:(a)10%CW，(b)30%CW，(c)60%CW，(d)90%CW(250倍）。24©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.10Anisotropicbehaviorinarolledaluminum-lithiumsheetmaterialusedinaerospaceapplications.Thesketchrelatesthepositionoftensilebarstothemechanicalpropertiesthatareobtained用于航空领域的轧制铝-锂薄片的各向异性形为。示意图所示为拉力试棒的位置与所测得的机械性能之间的关系。屈服强度抗张强度伸长率25Example7.3DesignofaStampingProcess冲压过程的设计Onemethodforproducingfansforcoolingautomotiveandtruckenginesistostampthebladesfromcold-rolledsteelsheet,thenattachthebladestoa“spider’’thatholdsthebladesintheproperposition.Anumberoffanblades,allproducedatthesametime,havefailedbytheinitiationandpropagationofafatiguecracktransversetotheaxisoftheblade(Figure7.11).Allotherfanbladesperformsatisfactorily.Provideanexplanationforthefailureofthebladesandredesignthemanufacturingprocesstopreventthesefailures.一种制造用于冷却汽车和卡车发动机的风扇的方式是首先将冷轧钢板冲压成叶片，然后将叶片固定在一个“十字架”上以使得叶片处于适当的位置。在同时生产的叶片中，一定数量的叶片会因为疲劳裂纹的产生和裂纹扩展而报废，所产生的裂纹与叶片的轴垂直(Figure7.11)

，其它叶片的质量则令人满意。解释叶片报废的原因并重新设计制造过程以防止废品产生。26©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.11Orientationsofsamples(forExample7.3)试样的方位Example7.3(continued)轧制方向

想要的

不想要的

27Example7.3SOLUTIONThewrongtypeofsteelmayhavebeenselected.可能选择了型号不正确的钢板。Thediesusedtostampthebladesfromthesheetmaybeworn.由钢板冲压叶片所使用的模具可能旧了。Theclearancebetweenthepartsofthediesmaybeincorrect,producingdefectsthatinitiatefatiguefailure.模具各个部件之间的间隙可能不正确，产生的缺陷引起疲劳破坏。Thefailurescouldalsoberelatedtotheanisotropicbehaviorofthesteelsheetcausedbyrolling.废品也可能与轧制钢板时材料产生的各向异性行为有关。28©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.12Thecompressiveresidualstressescanbeharmfulorbeneficial.(a)Abendingforceappliesatensilestressonthetopofthebeam.Sincetherearealreadytensileresidualstressesatthetop,theload-carryingcharacteristicsarepoor.(b)Thetopcontainscompressiveresidualstresses.Nowtheload-carryingcharacteristicsareverygoods.残余压应力可能是有害的或有益的。(a)一个弯曲力在梁的顶部产生张应力。因为在顶部已经存在残余张应力，承载能力差。(b)顶部存在残余压应力，承载能力非常好。29Example7.4DesignofaFatigue-ResistantShaft抗疲劳轴的设计Yourcompanyhasproducedseveralthousandshaftsthathaveafatiguestrengthof20,000psi.Theshaftsaresubjectedtohigh-bendingloadsduringrotation.Yoursalesengineersreportthatthefirstfewshaftsplacedintoservicefailedinashortperiodoftimebyfatigue.Designaprocessbywhichtheremainingshaftscanbesalvagedbyimprovingtheirfatigueproperties.你的公司生产了数千根疲劳强度为20,000psi的轴，该轴在转动过程中承受高弯曲载荷。你的经销人员报告因为疲劳最初的几根轴在短期内就损坏了，设计处理方法通过改善轴的疲劳性能来挽救剩余的轴。30Example7.4SOLUTIONIncreasingthestrengthatthesurfaceimprovesthefatiguelifeoftheshaft–carburizing提高表面强度改善轴的疲劳寿命-渗碳处理Coldworkingtheshaft对轴进行冷加工Shotpeentheshaft轴（表面）喷丸强化喷丸强化分为一般喷丸和应力喷丸.一般处理时,钢板在自由状态下,用高速钢丸打击钢板的里面,使其表面产生预压应力.以减少工作中钢板表面的拉应力,增加使用寿命.应力喷丸处理是将钢板在一定的作用力下的预先弯曲,然后进行喷丸处理.

31Figure7.13Shotpeentheshaft轴（表面）喷丸强化32Section7.5CharacteristicsofColdWorking冷加工的特性

©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.14Acomparisonofstrengtheningcopperby(a)coldworkingand(b)alloyingwithzinc.Notethatcoldworkingproducesgreaterstrengthening,yethaslittleeffectonelectricalconductivity.比较铜的强化效果(a)通过冷加工强化(b)与锌形成合金强化。注意冷加工导致更高的强度，但是对电导率的影响小。屈服强度33©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.15Thewire-drawingprocess.TheforceFdactsonboththeoriginalandfinaldiameters.Thus,thestressproducedinthefinalwireisgreaterthanthatintheoriginal.Ifthewiredidnotstrainhardenduringdrawing,thefinalwirewouldbreakbeforetheoriginalwirewasdrawnthroughthedie.金属丝-拉拔加工。拉力Fd同时作用于前后两种直径的丝上，因此，作用在最终的丝上的应力要高于作用在初始丝上的应力，如果在拉拔加工过程中没有出现应变硬化，在初始丝被拉出模具之前，最终的丝就将会断裂。34Section7.6TheThreeStagesofAnnealing退火的三个阶段Recovery

-Alow-temperatureannealingheattreatmentdesignedtoeliminateresidualstressesintroducedduringdeformationwithoutreducingthestrengthofthecold-workedmaterial.回复

–退火热处理低温阶段，作用是消除变形过程中产生的残余应力，被冷加工的材料强度不降低。Recrystallization-Amedium-temperatureannealingheattreatmentdesignedtoeliminatealloftheeffectsofthestrainhardeningproducedduringcoldworking.再结晶

-退火热处理中温阶段，作用是消除冷加工过程中应变硬化效果。Graingrowth

-Movementofgrainboundariesbydiffusioninordertoreducetheamountofgrainboundaryarea.晶粒长大–因扩散导致晶粒边界移动以减少晶粒边界的面积。35Figure7.16Photomicrographsshowingtheeffectofannealingtemperatureongrainsizeinbrass.Twinboundariescanalsobeobservedinthestructures.(a)Annealedat400oC,(b)annealedat650oC,and(c)annealedat800oC(75).退火处理温度对黄铜中晶粒尺寸的影响(a)400oC退火，(b)650oC退火，(c)800oC退火。36©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.17Theeffectofannealingtemperatureonthemicrostructureofcold-workedmetals.(a)cold-worked,(b)afterrecovery,(c)afterrecrystallization,and(d)aftergraingrowth.退火温度对冷加工材料微观结构的影响。(a)冷加工材料，(b)回复阶段后，(c)再结晶后，(d)晶粒长大后。37Section7.7ControlofAnnealing退火的控制

Warmworking-Atermusedtoindicatetheprocessingofmetallicmaterialsinatemperaturerangethatisbetweenthosethatdefinecoldandhotworking(usuallyatemperaturebetween0.3to0.6ofmeltingtemperatureinK).温加工

–用于表示金属材料处理的术语，处理的温度是介于冷加工和热加工之间，（以K为温度单位，通常是在熔点的0.3到0.6倍之间）。38©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.19Longerannealingtimesreducetherecrystallizationtemperature.Notethattherecrystallizationtemperatureisnotafixedtemperature.更长的退火时间降低再结晶温度。注意再结晶的温度不是固定不变的。3940Section7.8AnnealingandMaterialsProcessing退火和材料处理

Heat-affectedzone(HAZ)–Thevolumeofmaterialadjacenttoaweldthatisheatedduringtheweldingprocessabovesomecriticaltemperatureatwhichachangeinthestructure,suchasgraingrowthorrecrystallization,occurs.热影响区

(HAZ)–材料邻近焊接点的区域，这个区域在焊接过程中受热超过了某个引起材料结构变化的临界温度，例如晶粒长大或再结晶发生。41©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure7.20Thestructu