ch07-應變硬化與退火-E-2

1TheScienceandEngineeringofMaterials,4thed2003

DonaldR.Askeland–PradeepP.PhuléChapter7–StrainHardeningandAnnealing應變硬化(加工硬化)與退火2IntroductiontoChapter1Thetetrahedronofmaterialsscienceandengineering

材料科學與工程四面體3Reviewofknowledge知識回顧Chapter1–IntroductiontoMaterialsScienceandEngineering

緒論Chapter2–AtomicStructure原子結構Chapter3–AtomicandIonicArrangements

原子和離子的排列Chapter4–ImperfectionsintheAtomicandIonicArrangements原子和離子排列中的缺陷Chapter5–AtomandIonMovementsinMaterials

材料中原子和離子的運動Chapter6–MechanicalPropertiesandBehavior

機械性質與行為4

ObjectivesofChapter7第七章目標Tolearnhowthestrengthofmetalsandalloysisinfluencedbymechanicalprocessingandheattreatments.學習機械加工和熱處理如何影響金屬和合金的強度。Tolearnhowtoenhancethestrengthofmetalsandalloysusingcoldworking.學習如何利用冷加工提高金屬和合金的強度Tolearnhowtoenhanceductilityusingannealingheattreatment.學習如何利用退火提高展延性5ChapterOutline本章概要7.1RelationshipofColdWorkingtotheStress-StrainCurve冷加工與應力-應變曲線的關聯7.2

Strain-HardeningMechanisms應變硬化的機理7.3PropertiesversusPercentColdWork（%CW）

性質與%CW7.4Microstructure,TextureStrengthening,andResidualStresses微觀結構，織構強化，殘余應力7.5CharacteristicsofColdWorking冷加工的特性7.6TheThreeStagesofAnnealing退火的三個階段7.7ControlofAnnealing退火的控制7.8AnnealingandMaterialsProcessing退火和材料處理7.9HotWorking熱加工7.10SuperplasticForming(SPF)超塑性成型6

Section7.1RelationshipofColdWorkingtotheStress-StrainCurve冷加工與應力-應變曲線的關聯

Strainhardening應變硬化Strainhardeningexponent(n)

應變硬化指數（n）7應變硬化Strainhardening金屬材料在再結晶溫度以下塑性變形時強度和硬度升高，而塑性和韌性降低的現象。又稱冷作硬化。產生原因是，金屬在塑性變形時，晶粒發(fā)生滑移，出現位錯的纏結，使晶粒拉長、破碎和纖維化，金屬內部產生了殘余應力等。加工硬化的程度通常用加工后與加工前表面層顯微硬度的比值和硬化層深度來表示。

加工硬化給金屬件的進一步加工帶來困難。如在冷軋鋼板的過程中會愈軋愈硬以致軋不動，因而需在加工過程中安排中間退火，通過加熱消除其加工硬化。又如在切削加工中使工件表層脆而硬，從而加速刀具磨損、增大切削力等。但有利的一面是，它可提高金屬的強度、硬度和耐磨性，特別是對于那些不能以熱處理方法提高強度的純金屬和某些合金尤為重要。如冷拉高強度鋼絲和冷卷彈簧等，就是利用冷加工變形來提高其強度和彈性極限。又如坦克和拖拉機的履帶、破碎機的顎板以及鐵路的道岔等也是利用加工硬化來提高其硬度和耐磨性的。

8Figure7.2Manufacturingprocessesthatmakeuseofcoldworkingaswellashotworking.Commonmetalworkingmethods冷加工及熱加工過程。普通的金屬加工方式。Forging鍛造Extruding擠壓Drawing拉拔Stamping沖壓Rolling軋制9Strainhardeningexponent(n)應變硬化指數（n）在金屬材料拉伸真應力應變曲線上的均勻塑性變形階段關系式：σ

=kεn

（σ：真應力，

ε：真應變）

應變硬化指數n反映了金屬材料抵抗繼續(xù)塑性變形的能力，是表征金屬材料應變硬化的性能指標。

在極限情況下，n＝1，表示材料為完全理想的彈性體，σ與ε

成正比關系；

n＝0時，σ＝k＝常數，表示材料沒有應變硬化能力，例如室溫下產生再結晶的軟金屬及已受強烈應變硬化的材料。大多數金屬的n值在0.1~0.5之間。10?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.3Thetruestress-truestraincurvesformetalswithlargeandsmallstrain-hardeningexponents.Largerdegreesofstrengtheningareobtainedforagivenstrainforthemetalwiththelargern具有大的和小的應變硬化指數（n）的金屬的真應力-應變曲線，當應變給定時，具有較大n的金屬的應變硬化程度更大。lnσ=lnK+nlnε11典型金屬和合金的應變硬化指數和強度系數磅力/英寸2(psi)=psi=磅力/英寸2鈦鉬奧氏體不銹鋼淬火和回火中碳鋼退火合金鋼12Section7.2Strain-HardeningMechanisms應變硬化的機理

Frank-Readsource-Apinneddislocationthat,underanappliedstress,producesadditionaldislocations.Thismechanismisatleastpartlyresponsibleforstrainhardening.弗蘭克-瑞德源–一個被釘住的位錯，在外加應力的作用下，引起額外的位錯。這一機制至少是引起應變硬化的部分原因。Thermoplastics-Aclassofpolymersthatconsistoflarge,longspaghetti-likemoleculesthatareintertwined(e.g.,polyethylene,nylon,PET,etc.).

熱塑性塑料

–一類由長鏈大分子相互纏繞組成的聚合物（例如，聚乙烯，尼龍，聚對苯二甲酸乙二酯等。）13Figure7.5TheFrank-Readsourcecangeneratedislocations.(a)Adislocationispinnedatitsendsbylatticedefects.(b)Asthedislocationcontinuestomove,thedislocationbows,eventuallybendingbackonitself.(c)finallythedislocationloopforms,and(d)anewdislocationiscreated.(e)ElectronmicrographofaFrank-Readsource(330,000).弗蘭克-瑞德源能產生位錯。(a)一個位錯被它兩端的晶格缺陷固定。(b)當位錯連續(xù)運動，該位錯變成弓形，最終折回。(c)最后該位錯成環(huán)形。(d)形成新的位錯。(e)弗蘭克-瑞德源的電鏡照片（330000倍）14?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.6Inanundeformedthermoplasticpolymertensilebar,(a)thepolymerchainsarerandomlyoriented.(b)Whenastressisapplied,aneckdevelopsaschainsbecomealignedlocally.Theneckcontinuestogrowuntilthechainsintheentiregagelengthhavealigned.(c)Thestrengthofthepolymerisincreased在一個未變形的熱塑性塑料拉力試棒中，(a)聚合物分子鏈是隨機取向的。(b)當施加應力后，因分子鏈局部定向排列從而形成細頸。細頸增長直到所有分子鏈定向排列。(c)聚合物的強度被提高。15Section7.3PropertiesversusPercentColdWork性質與%CW

percent

coldwork的定義是冷加工前初始橫截面積與冷加工后最終橫截面積的變化百分比，其中包含多個中間過程對結果沒有影響。因此總的percent

coldwork實際上是:%CW=[(t0-tf)/t0]X100%16Section7.3PropertiesversusPercentColdWork性質與%CW

?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.7Theeffectofcoldworkonthemechanicalpropertiesofcopper冷加工對銅的機械性質的影響伸長率屈服強度抗張強度17Example7.1ColdWorkingaCopperPlate冷加工銅板

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

一塊厚度1cm的銅板，被冷加工至0.50cm厚，然后進一步冷加工至0.16cm厚。確定0.16cm厚的板材總的%CW和拉伸強度。18?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.8

Diagramshowingtherollingofa1-cmplate(forExample7.1)軋1cm板的示意圖19Example7.1SOLUTION20Example7.2DesignofaColdWorkingProcess設計冷加工工藝

Designamanufacturingprocesstoproducea0.1-cm-thickcopperplatehavingatleast65,000psitensilestrength,60,000psiyieldstrength,and5%elongation.設計一個制造工藝生產拉伸強度不低于65,000psi(磅力/英寸2)，屈服強度不低于60,000psi以及斷裂伸長不低于5%的0.1cm厚度的銅板。Example7.2SOLUTIONToproducetheplate,acold-rollingprocesswouldbeappropriate.TheoriginalthicknessofthecopperplatepriortorollingcanbecalculatedfromEquation7-4.Becausethereisarangeofallowablecoldwork—between40%and45%—thereisarangeofinitialplatethicknesses:要生產這種板材，冷軋工藝是適合的。冷軋之前銅板的初始厚度可通過%CW計算。因為允許的%CW在40%~45%范圍內（參見圖7-7），初始板材厚度范圍為：21Example7.2SOLUTION(Continued)Toproducethe0.1-cmcopperplate,webeginwitha0.167-to0.182-cmcopperplateinthesoftestpossiblecondition,thencoldrolltheplate40%to45%toachievethe0.1cmthickness.為生產0.1-cm的銅板，我們用盡可能軟的0.167至0.182cm的銅板，冷軋至%CW為40%~45%得到厚度為0.1cm的板材。22Section7.4Microstructure,TextureStrengthening,andResidualStresses微觀結構，織構強化，殘余應力

Fibertexture,Sheettexture纖維狀構造，薄片狀構造Polefigureanalysis,Orientationmicroscopy極圖分析,取向顯微術Residualstresses,Stress-reliefanneal殘余應力，消除應力退火Annealingglass,Temperedglass玻璃退火，鋼化玻璃23Figure7.9Thefibrousgrainstructureofalowcarbonsteelproducedbycoldworking:(a)10%coldwork,(b)30%coldwork,(c)60%coldwork,and(d)90%coldwork(250).冷加工得到的低碳鋼纖維狀晶粒結構:(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用于航空領域的軋制鋁-鋰薄片的各向異性形為。示意圖所示為拉力試棒的位置與所測得的機械性能之間的關系。屈服強度抗張強度伸長率25Example7.3DesignofaStampingProcess沖壓過程的設計Onemethodforproducingfansforcoolingautomotiveandtruckenginesistostampthebladesfromcold-rolledsteelsheet,thenattachthebladestoa“spider’’thatholdsthebladesintheproperposition.Anumberoffanblades,allproducedatthesametime,havefailedbytheinitiationandpropagationofafatiguecracktransversetotheaxisoftheblade(Figure7.11).Allotherfanbladesperformsatisfactorily.Provideanexplanationforthefailureofthebladesandredesignthemanufacturingprocesstopreventthesefailures.一種制造用于冷卻汽車和卡車發(fā)動機的風扇的方式是首先將冷軋鋼板沖壓成葉片，然后將葉片固定在一個“十字架”上以使得葉片處于適當的位置。在同時生產的葉片中，一定數量的葉片會因為疲勞裂紋的產生和裂紋擴展而報廢，所產生的裂紋與葉片的軸垂直(Figure7.11)

，其它葉片的質量則令人滿意。解釋葉片報廢的原因并重新設計制造過程以防止廢品產生。26?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.11Orientationsofsamples(forExample7.3)試樣的方位Example7.3(continued)軋制方向

想要的

不想要的

27Example7.3SOLUTIONThewrongtypeofsteelmayhavebeenselected.可能選擇了型號不正確的鋼板。Thediesusedtostampthebladesfromthesheetmaybeworn.由鋼板沖壓葉片所使用的模具可能舊了。Theclearancebetweenthepartsofthediesmaybeincorrect,producingdefectsthatinitiatefatiguefailure.模具各個部件之間的間隙可能不正確，產生的缺陷引起疲勞破壞。Thefailurescouldalsoberelatedtotheanisotropicbehaviorofthesteelsheetcausedbyrolling.廢品也可能與軋制鋼板時材料產生的各向異性行為有關。28?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.12Thecompressiveresidualstressescanbeharmfulorbeneficial.(a)Abendingforceappliesatensilestressonthetopofthebeam.Sincetherearealreadytensileresidualstressesatthetop,theload-carryingcharacteristicsarepoor.(b)Thetopcontainscompressiveresidualstresses.Nowtheload-carryingcharacteristicsareverygoods.殘余壓應力可能是有害的或有益的。(a)一個彎曲力在梁的頂部產生張應力。因為在頂部已經存在殘余張應力，承載能力差。(b)頂部存在殘余壓應力，承載能力非常好。29Example7.4DesignofaFatigue-ResistantShaft抗疲勞軸的設計Yourcompanyhasproducedseveralthousandshaftsthathaveafatiguestrengthof20,000psi.Theshaftsaresubjectedtohigh-bendingloadsduringrotation.Yoursalesengineersreportthatthefirstfewshaftsplacedintoservicefailedinashortperiodoftimebyfatigue.Designaprocessbywhichtheremainingshaftscanbesalvagedbyimprovingtheirfatigueproperties.你的公司生產了數千根疲勞強度為20,000psi的軸，該軸在轉動過程中承受高彎曲載荷。你的經銷人員報告因為疲勞最初的幾根軸在短期內就損壞了，設計處理方法通過改善軸的疲勞性能來挽救剩余的軸。30Example7.4SOLUTIONIncreasingthestrengthatthesurfaceimprovesthefatiguelifeoftheshaft–carburizing提高表面強度改善軸的疲勞壽命-滲碳處理Coldworkingtheshaft對軸進行冷加工Shotpeentheshaft軸（表面）噴丸強化噴丸強化分為一般噴丸和應力噴丸.一般處理時,鋼板在自由狀態(tài)下,用高速鋼丸打擊鋼板的里面,使其表面產生預壓應力.以減少工作中鋼板表面的拉應力,增加使用壽命.應力噴丸處理是將鋼板在一定的作用力下的預先彎曲,然后進行噴丸處理.

31Figure7.13Shotpeentheshaft軸（表面）噴丸強化32Section7.5CharacteristicsofColdWorking冷加工的特性

?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.14Acomparisonofstrengtheningcopperby(a)coldworkingand(b)alloyingwithzinc.Notethatcoldworkingproducesgreaterstrengthening,yethaslittleeffectonelectricalconductivity.比較銅的強化效果(a)通過冷加工強化(b)與鋅形成合金強化。注意冷加工導致更高的強度，但是對電導率的影響小。屈服強度33?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.15Thewire-drawingprocess.TheforceFdactsonboththeoriginalandfinaldiameters.Thus,thestressproducedinthefinalwireisgreaterthanthatintheoriginal.Ifthewiredidnotstrainhardenduringdrawing,thefinalwirewouldbreakbeforetheoriginalwirewasdrawnthroughthedie.金屬絲-拉拔加工。拉力Fd同時作用于前后兩種直徑的絲上，因此，作用在最終的絲上的應力要高于作用在初始絲上的應力，如果在拉拔加工過程中沒有出現應變硬化，在初始絲被拉出模具之前，最終的絲就將會斷裂。34Section7.6TheThreeStagesofAnnealing退火的三個階段Recovery

-Alow-temperatureannealingheattreatmentdesignedtoeliminateresidualstressesintroducedduringdeformationwithoutreducingthestrengthofthecold-workedmaterial.回復

–退火熱處理低溫階段，作用是消除變形過程中產生的殘余應力，被冷加工的材料強度不降低。Recrystallization-Amedium-temperatureannealingheattreatmentdesignedtoeliminatealloftheeffectsofthestrainhardeningproducedduringcoldworking.再結晶

-退火熱處理中溫階段，作用是消除冷加工過程中應變硬化效果。Graingrowth

-Movementofgrainboundariesbydiffusioninordertoreducetheamountofgrainboundaryarea.晶粒長大–因擴散導致晶粒邊界移動以減少晶粒邊界的面積。35Figure7.16Photomicrographsshowingtheeffectofannealingtemperatureongrainsizeinbrass.Twinboundariescanalsobeobservedinthestructures.(a)Annealedat400oC,(b)annealedat650oC,and(c)annealedat800oC(75).退火處理溫度對黃銅中晶粒尺寸的影響(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.退火溫度對冷加工材料微觀結構的影響。(a)冷加工材料，(b)回復階段后，(c)再結晶后，(d)晶粒長大后。37Section7.7ControlofAnnealing退火的控制

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

–用于表示金屬材料處理的術語，處理的溫度是介于冷加工和熱加工之間，（以K為溫度單位，通常是在熔點的0.3到0.6倍之間）。38?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.19Longerannealingtimesreducetherecrystallizationtemperature.Notethattherecrystallizationtemperatureisnotafixedtemperature.更長的退火時間降低再結晶溫度。注意再結晶的溫度不是固定不變的。3940Section7.8AnnealingandMaterialsProcessing退火和材料處理

Heat-affectedzone(HAZ)–Thevolumeofmaterialadjacenttoaweldthatisheatedduringtheweldingprocessabovesomecriticaltemperatureatwhichachangeinthestructure,suchasgraingrowthorrecrystallization,occurs.熱影響區(qū)

(HAZ)–材料鄰近焊接點的區(qū)域，這個區(qū)域在焊接過程中受熱超過了某個引起材料結構變化的臨界溫度，例如晶粒長大或再結晶發(fā)生。41?2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning?isatrademarkusedhereinunderlicense.Figure7.20Thestructu