機械工程第二版英語翻譯

./目錄1·2·7·8·11·12單元第一單元? TypesofMaterials材料的類型Materialsmaybegroupedinseveralways.Scientistsoftenclassifymaterialsbytheirstate:solid,liquid,orgas.Theyalsoseparatethemintoorganic<onceliving>andinorganic<neverliving>materials.材料可以按多種方法分類.科學家常根據(jù)狀態(tài)將材料分為：固體、液體或氣體.他們也把材料分為有機材料<曾經(jīng)有生命的>和無機材料<從未有生命的>.Forindustrialpurposes,materialsaredividedintoengineeringmaterialsornonengineeringmaterials.Engineeringmaterialsarethoseusedinmanufactureandbecomepartsofproducts.就工業(yè)效用而言,材料被分為工程材料和非工程材料.那些用于加工制造并成為產(chǎn)品組成部分的就是工程材料.Nonengineeringmaterialsarethechemicals,fuels,lubricants,andothermaterialsusedinthemanufacturingprocess,whichdonotbecomepartoftheproduct.非工程材料則是化學品、燃料、潤滑劑以及其它用于加工制造過程但不成為產(chǎn)品組成部分的材料.Engineeringmaterialsmaybefurthersubdividedinto:①Metal②Ceramics③Composite④Polymers,etc.工程材料還能進一步細分為：①金屬材料②陶瓷材料③復合材料④聚合材料,等等.? MetalsandMetalAlloys金屬和金屬合金Metalsareelementsthatgenerallyhavegoodelectricalandthermalconductivity.Manymetalshavehighstrength,highstiffness,andhavegoodductility.金屬就是通常具有良好導電性和導熱性的元素.許多金屬具有高強度、高硬度以及良好的延展性.Somemetals,suchasiron,cobaltandnickel,aremagnetic.Atlowtemperatures,somemetalsandintermetalliccompoundsbecomesuperconductors.某些金屬能被磁化,例如鐵、鈷和鎳.在極低的溫度下,某些金屬和金屬化合物能轉變成超導體.Whatisthedifferencebetweenanalloyandapuremetal?Puremetalsareelementswhichcomefromaparticularareaoftheperiodictable.Examplesofpuremetalsincludecopperinelectricalwiresandaluminumincookingfoilandbeveragecans.合金與純金屬的區(qū)別是什么？純金屬是在元素周期表中占據(jù)特定位置的元素.例如電線中的銅和制造烹飪箔及飲料罐的鋁.Alloyscontainmorethanonemetallicelement.Theirpropertiescanbechangedbychangingtheelementspresentinthealloy.Examplesofmetalalloysincludestainlesssteelwhichisanalloyofiron,nickel,andchromium;andgoldjewelrywhichusuallycontainsanalloyofgoldandnickel.合金包含不止一種金屬元素.合金的性質能通過改變其中存在的元素而改變.金屬合金的例子有：不銹鋼是一種鐵、鎳、鉻的合金,以及金飾品通常含有金鎳合金.Whyaremetalsandalloysused?Manymetalsandalloyshavehighdensitiesandareusedinapplicationswhichrequireahighmass-to-volumeratio.為什么要使用金屬和合金？許多金屬和合金具有高密度,因此被用在需要較高質量體積比的場合.Somemetalalloys,suchasthosebasedonaluminum,havelowdensitiesandareusedinaerospaceapplicationsforfueleconomy.Manyalloysalsohavehighfracturetoughness,whichmeanstheycanwithstandimpactandaredurable.某些金屬合金,例如鋁基合金,其密度低,可用于航空航天以節(jié)約燃料.許多合金還具有高斷裂韌性,這意味著它們能經(jīng)得起沖擊并且是耐用的.Whataresomeimportantpropertiesofmetals?Densityisdefinedasamaterial’smassdividedbyitsvolume.Mostmetalshaverelativelyhighdensities,especiallycomparedtopolymers.金屬有哪些重要特性？密度定義為材料的質量與其體積之比.大多數(shù)金屬密度相對較高,尤其是和聚合物相比較而言.Materialswithhighdensitiesoftencontainatomswithhighatomicnumbers,suchasgoldorlead.However,somemetalssuchasaluminumormagnesiumhavelowdensities,andareusedinapplicationsthatrequireothermetallicpropertiesbutalsorequirelowweight.高密度材料通常由較大原子序數(shù)原子構成,例如金和鉛.然而,諸如鋁和鎂之類的一些金屬則具有低密度,并被用于既需要金屬特性又要求重量輕的場合.Fracturetoughnesscanbedescribedasamaterial’sabilitytoavoidfracture,especiallywhenaflawisintroduced.Metalscangenerallycontainnicksanddentswithoutweakeningverymuch,andareimpactresistant.Afootballplayercountsonthiswhenhetruststhathisfacemaskwon’tshatter.斷裂韌性可以描述為材料防止斷裂特別是出現(xiàn)缺陷時不斷裂的能力.金屬一般能在有缺口和凹痕的情況下不顯著削弱,并且能抵抗沖擊.橄欖球運動員據(jù)此相信他的面罩不會裂成碎片.Plasticdeformationistheabilityofbendordeformbeforebreaking.Asengineers,weusuallydesignmaterialssothattheydon’tdeformundernormalconditions.Youdon’twantyourcartoleantotheeastafterastrongwestwind.塑性變形就是在斷裂前彎曲或變形的能力.作為工程師,設計時通常要使材料在正常條件下不變形.沒有人愿意一陣強烈的西風過后自己的汽車向東傾斜.However,sometimeswecantakeadvantageofplasticdeformation.Thecrumplezonesinacarabsorbenergybyundergoingplasticdeformationbeforetheybreak.然而,有時我們也能利用塑性變形.汽車上壓皺的區(qū)域在它們斷裂前通過經(jīng)歷塑性變形來吸收能量.Theatomicbondingofmetalsalsoaffectstheirproperties.Inmetals,theoutervalenceelectronsaresharedamongallatoms,andarefreetotraveleverywhere.Sinceelectronsconductheatandelectricity,metalsmakegoodcookingpansandelectricalwires.金屬的原子連結對它們的特性也有影響.在金屬內部,原子的外層階電子由所有原子共享并能到處自由移動.由于電子能導熱和導電,所以用金屬可以制造好的烹飪鍋和電線.Itisimpossibletoseethroughmetals,sincethesevalenceelectronsabsorbanyphotonsoflightwhichreachthemetal.Nophotonspassthrough.因為這些階電子吸收到達金屬的光子,所以透過金屬不可能看得見.沒有光子能通過金屬.Alloysarecompoundsconsistingofmorethanonemetal.Addingothermetalscanaffectthedensity,strength,fracturetoughness,plasticdeformation,electricalconductivityandenvironmentaldegradation.合金是由一種以上金屬組成的混合物.加一些其它金屬能影響密度、強度、斷裂韌性、塑性變形、導電性以及環(huán)境侵蝕.Forexample,addingasmallamountofirontoaluminumwillmakeitstronger.Also,addingsomechromiumtosteelwillslowtherustingprocess,butwillmakeitmorebrittle.例如,往鋁里加少量鐵可使其更強.同樣,在鋼里加一些鉻能減緩它的生銹過程,但也將使它更脆.? CeramicsandGlasses陶瓷和玻璃Aceramicisoftenbroadlydefinedasanyinorganicnonmetallicmaterial．Bythisdefinition,ceramicmaterialswouldalsoincludeglasses;however,manymaterialsscientistsaddthestipulationthat"ceramic"mustalsobecrystalline.陶瓷通常被概括地定義為無機的非金屬材料.照此定義,陶瓷材料也應包括玻璃；然而許多材料科學家添加了"陶瓷"必須同時是晶體物組成的約定.Aglassisaninorganicnonmetallicmaterialthatdoesnothaveacrystallinestructure.Suchmaterialsaresaidtobeamorphous.玻璃是沒有晶體狀結構的無機非金屬材料.這種材料被稱為非結晶質材料.PropertiesofCeramicsandGlassesSomeoftheusefulpropertiesofceramicsandglassesincludehighmeltingtemperature,lowdensity,highstrength,stiffness,hardness,wearresistance,andcorrosionresistance.陶瓷和玻璃的特性高熔點、低密度、高強度、高剛度、高硬度、高耐磨性和抗腐蝕性是陶瓷和玻璃的一些有用特性.Manyceramicsaregoodelectricalandthermalinsulators.Someceramicshavespecialproperties:someceramicsaremagneticmaterials;somearepiezoelectricmaterials;andafewspecialceramicsaresuperconductorsatverylowtemperatures.Ceramicsandglasseshaveonemajordrawback:theyarebrittle.許多陶瓷都是電和熱的良絕緣體.某些陶瓷還具有一些特殊性能：有些是磁性材料,有些是壓電材料,還有些特殊陶瓷在極低溫度下是超導體.陶瓷和玻璃都有一個主要的缺點：它們容易破碎.Ceramicsarenottypicallyformedfromthemelt.Thisisbecausemostceramicswillcrackextensively<i.e.formapowder>uponcoolingfromtheliquidstate.陶瓷一般不是由熔化形成的.因為大多數(shù)陶瓷在從液態(tài)冷卻時將會完全破碎<即形成粉末>.Hence,allthesimpleandefficientmanufacturingtechniquesusedforglassproductionsuchascastingandblowing,whichinvolvethemoltenstate,cannotbeusedfortheproductionofcrystallineceramics.Instead,"sintering"or"firing"istheprocesstypicallyused.因此,所有用于玻璃生產(chǎn)的簡單有效的—諸如澆鑄和吹制這些涉及熔化的技術都不能用于由晶體物組成的陶瓷的生產(chǎn).作為替代,一般采用"燒結"或"焙燒"工藝.Insintering,ceramicpowdersareprocessedintocompactedshapesandthenheatedtotemperaturesjustbelowthemeltingpoint.Atsuchtemperatures,thepowdersreactinternallytoremoveporosityandfullydensearticlescanbeobtained.在燒結過程中,陶瓷粉末先擠壓成型然后加熱到略低于熔點溫度.在這樣的溫度下,粉末內部起反應去除孔隙并得到十分致密的物品.Anopticalfibercontainsthreelayers:acoremadeofhighlypureglasswithahighrefractiveindexforthelighttotravel,amiddlelayerofglasswithalowerrefractiveindexknownasthecladdingwhichprotectsthecoreglassfromscratchesandothersurfaceimperfections,andanoutpolymerjackettoprotectthefiberfromdamage.光導纖維有三層：核心由高折射指數(shù)高純光傳輸玻璃制成,中間層為低折射指數(shù)玻璃,是保護核心玻璃表面不被擦傷和完整性不被破壞的所謂覆層,外層是聚合物護套,用于保護光導纖維不受損.Inorderforthecoreglasstohaveahigherrefractiveindexthanthecladding,thecoreglassisdopedwithasmall,controlledamountofanimpurity,ordopant,whichcauseslighttotravelslower,butdoesnotabsorbthelight.為了使核心玻璃有比覆層大的折射指數(shù),在其中摻入微小的、可控數(shù)量的能減緩光速而不會吸收光線的雜質或攙雜劑.Becausetherefractiveindexofthecoreglassisgreaterthanthatofthecladding,lighttravelinginthecoreglasswillremaininthecoreglassduetototalinternalreflectionaslongasthelightstrikesthecore/claddinginterfaceatananglegreaterthanthecriticalangle.由于核心玻璃的折射指數(shù)比覆層大,只要在全內反射過程中光線照射核心/覆層分界面的角度比臨界角大,在核心玻璃中傳送的光線將仍保留在核心玻璃中.Thetotalinternalreflectionphenomenon,aswellasthehighpurityofthecoreglass,enableslighttotravellongdistanceswithlittlelossofintensity.全內反射現(xiàn)象與核心玻璃的高純度一樣,使光線幾乎無強度損耗傳遞長距離成為可能.? Composites復合材料Compositesareformedfromtwoormoretypesofmaterials.Examplesincludepolymer/ceramicandmetal/ceramiccomposites.Compositesareusedbecauseoverallpropertiesofthecompositesaresuperiortothoseoftheindividualcomponents.復合材料由兩種或更多材料構成.例子有聚合物/陶瓷和金屬/陶瓷復合材料.之所以使用復合材料是因為其全面性能優(yōu)于組成部分單獨的性能.Forexample:polymer/ceramiccompositeshaveagreatermodulusthanthepolymercomponent,butaren’tasbrittleasceramics.Twotypesofcompositesare:fiber-reinforcedcompositesandparticle-reinforcedcomposites.例如：聚合物/陶瓷復合材料具有比聚合物成分更大的模量,但又不像陶瓷那樣易碎.復合材料有兩種：纖維加強型復合材料和微粒加強型復合材料.Fiber-reinforcedCompositesReinforcingfiberscanbemadeofmetals,ceramics,glasses,orpolymersthathavebeenturnedintographiteandknownascarbonfibers.Fibersincreasethemodulusofthematrixmaterial.纖維加強型復合材料加強纖維可以是金屬、陶瓷、玻璃或是已變成石墨的被稱為碳纖維的聚合物.纖維能加強基材的模量.Thestrongcovalentbondsalongthefiber’slengthgivethemaveryhighmodulusinthisdirectionbecausetobreakorextendthefiberthebondsmustalsobebrokenormoved.沿著纖維長度有很強結合力的共價結合在這個方向上給予復合材料很高的模量,因為要損壞或拉伸纖維就必須破壞或移除這種結合.Fibersaredifficulttoprocessintocomposites,makingfiber-reinforcedcompositesrelativelyexpensive.把纖維放入復合材料較困難,這使得制造纖維加強型復合材料相對昂貴.Fiber-reinforcedcompositesareusedinsomeofthemostadvanced,andthereforemostexpensivesportsequipment,suchasatime-trialracingbicycleframewhichconsistsofcarbonfibersinathermosetpolymermatrix.纖維加強型復合材料用于某些最先進也是最昂貴的運動設備,例如計時賽競賽用自行車骨架就是用含碳纖維的熱固塑料基材制成的.Bodypartsofracecarsandsomeautomobilesarecompositesmadeofglassfibers<orfiberglass>inathermosetmatrix.競賽用汽車和某些機動車的車體部件是由含玻璃纖維<或玻璃絲>的熱固塑料基材制成的.Fibershaveaveryhighmodulusalongtheiraxis,buthavealowmodulusperpendiculartotheiraxis.Fibercompositemanufacturersoftenrotatelayersoffiberstoavoiddirectionalvariationsinthemodulus.纖維在沿著其軸向有很高的模量,但垂直于其軸向的模量卻較低.纖維復合材料的制造者往往旋轉纖維層以防模量產(chǎn)生方向變化.Particle-reinforcedcompositesParticlesusedforreinforcingincludeceramicsandglassessuchassmallmineralparticles,metalparticlessuchasaluminum,andamorphousmaterials,includingpolymersandcarbonblack.微粒加強型復合材料用于加強的微粒包含了陶瓷和玻璃之類的礦物微粒,鋁之類的金屬微粒以及包括聚合物和碳黑的非結晶質微粒.Particlesareusedtoincreasethemodulusofthematrix,todecreasethepermeabilityofthematrix,todecreasetheductilityofthematrix.Anexampleofparticle-reinforcedcompositesisanautomobiletirewhichhascarbonblackparticlesinamatrixofpolyisobutyleneelastomericpolymer.微粒用于增加基材的模量、減少基材的滲透性和延展性.微粒加強型復合材料的一個例子是機動車胎,它就是在聚異丁烯人造橡膠聚合物基材中加入了碳黑微粒.? Polymers聚合材料Apolymerhasarepeatingstructure,usuallybasedonacarbonbackbone.Therepeatingstructureresultsinlargechainlikemolecules.Polymersareusefulbecausetheyarelightweight,corrosionresistant,easytoprocessatlowtemperaturesandgenerallyinexpensive.聚合物具有一般是基于碳鏈的重復結構.這種重復結構產(chǎn)生鏈狀大分子.由于重量輕、耐腐蝕、容易在較低溫度下加工并且通常較便宜,聚合物是很有用的.Someimportantcharacteristicsofpolymersincludetheirsize<ormolecularweight>,softeningandmeltingpoints,crystallinity,andstructure.Themechanicalpropertiesofpolymersgenerallyincludelowstrengthandhightoughness.Theirstrengthisoftenimprovedusingreinforcedcompositestructures.聚合材料具有一些重要特性,包括尺寸<或分子量>、軟化及熔化點、結晶度和結構.聚合材料的機械性能一般表現(xiàn)為低強度和高韌性.它們的強度通?？刹捎眉訌姀秃辖Y構來改善.ImportantCharacteristicsofPolymersSize.Singlepolymermoleculestypicallyhavemolecularweightsbetween10,000and1,000,000g/mol—thatcanbemorethan2,000repeatingunitsdependingonthepolymerstructure!聚合材料的重要特性尺寸：單個聚合物分子一般分子量為10,000到1,000,000g/mol之間,具體取決于聚合物的結構—這可以比2,000個重復單元還多.Themechanicalpropertiesofapolymeraresignificantlyaffectedbythemolecularweight,withbetterengineeringpropertiesathighermolecularweights.聚合物的分子量極大地影響其機械性能,分子量越大,工程性能也越好.Thermaltransitions.Thesofteningpoint<glasstransitiontemperature>andthemeltingpointofapolymerwilldeterminewhichitwillbesuitableforapplications.Thesetemperaturesusuallydeterminetheupperlimitforwhichapolymercanbeused.熱轉換性：聚合物的軟化點<玻璃狀轉化溫度>和熔化點決定了它是否適合應用.這些溫度通常決定聚合物能否使用的上限.Forexample,manyindustriallyimportantpolymershaveglasstransitiontemperaturesneartheboilingpointofwater<100℃,212℉>,andtheyaremostusefulforroomtemperatureapplications.Somespeciallyengineeredpolymerscanwithstandtemperaturesashighas300℃<572℉>.例如,許多工業(yè)上的重要聚合物其玻璃狀轉化溫度接近水的沸點<100℃,212℉>,它們被廣泛用于室溫下.而某些特別制造的聚合物能經(jīng)受住高達300℃<572℉>的溫度.Crystallinity.Polymerscanbecrystallineoramorphous,buttheyusuallyhaveacombinationofcrystallineandamorphousstructures<semi-crystalline>.結晶度：聚合物可以是晶體狀的或非結晶質的,但它們通常是晶體狀和非結晶質結構的結合物<半晶體>.Interchaininteractions.Thepolymerchainscanbefreetoslidepastoneanother<thermo-plastic>ortheycanbeconnectedtoeachotherwithcrosslinks<thermosetorelastomer>.Thermo-plasticscanbereformedandrecycled,whilethermosetsandelastomersarenotreworkable.原子鏈間的相互作用：聚合物的原子鏈可以自由地彼此滑動<熱可塑性>或通過交鍵互相連接<熱固性或彈性>.熱可塑性材料可以重新形成和循環(huán)使用,而熱固性與彈性材料則是不能再使用的.Intrachainstructure.Thechemicalstructureofthechainsalsohasatremendouseffectontheproperties.Dependingonthestructurethepolymermaybehydrophilicorhydrophobic<likesorhateswater>,stifforflexible,crystallineoramorphous,reactiveorunreactive.鏈內結構：原子鏈的化學結構對性能也有很大影響.根據(jù)各自的結構不同,聚合物可以是親水的或憎水的<喜歡或討厭水>、硬的或軟的、晶體狀的或非結晶質的、易起反應的或不易起反應的.第二單元Theunderstandingofheattreatmentisembracedbythebroaderstudyofmetallurgy.Metallurgyisthephysics,chemistry,andengineeringrelatedtometalsfromoreextractiontothefinalproduct.對熱處理的理解包含于對冶金學較廣泛的研究.冶金學是物理學、化學和涉及金屬從礦石提煉到最后產(chǎn)物的工程學.Heattreatmentistheoperationofheatingandcoolingametalinitssolidstatetochangeitsphysicalproperties.Accordingtotheprocedureused,steelcanbehardenedtoresistcuttingactionandabrasion,oritcanbesoftenedtopermitmachining.熱處理是將金屬在固態(tài)加熱和冷卻以改變其物理性能的操作.按所采用的步驟,鋼可以通過硬化來抵抗切削和磨損,也可以通過軟化來允許機加工.Withtheproperheattreatmentinternalstressesmayberemoved,grainsizereduced,toughnessincreased,orahardsurfaceproducedonaductileinterior.Theanalysisofthesteelmustbeknownbecausesmallpercentagesofcertainelements,notablycarbon,greatlyaffectthephysicalproperties.使用合適的熱處理可以去除內應力、細化晶粒、增加韌性或在柔軟材料上覆蓋堅硬的表面.因為某些元素<尤其是碳>的微小百分比極大地影響物理性能,所以必須知道對鋼的分析.Alloysteelowetheirpropertiestothepresenceofoneormoreelementsotherthancarbon,namelynickel,chromium,manganese,molybdenum,tungsten,silicon,vanadium,andcopper.Becauseoftheirimprovedphysicalpropertiestheyareusedcommerciallyinmanywaysnotpossiblewithcarbonsteels.合金鋼的性質取決于其所含有的除碳以外的一種或多種元素,如鎳、鉻、錳、鉬、鎢、硅、釩和銅.由于合金鋼改善的物理性能,它們被大量使用在許多碳鋼不適用的地方.Thefollowingdiscussionappliesprincipallytotheheattreatmentofordinarycommercialsteelsknownasplaincarbonsteels.Withthisprocesstherateofcoolingisthecontrollingfactor,rapidcoolingfromabovethecriticalrangeresultsinhardstructure,whereasveryslowcoolingproducestheoppositeeffect.下列討論主要針對被稱為普通碳鋼的工業(yè)用鋼而言.熱處理時冷卻速率是控制要素,從高于臨界溫度快速冷卻導致堅硬的組織結構,而緩慢冷卻則產(chǎn)生相反效果.? ASimplifiedIron-carbonDiagram簡化鐵碳狀態(tài)圖Ifwefocusonlyonthematerialsnormallyknownassteels,asimplifieddiagramisoftenused.如果只把注意力集中于一般所說的鋼上,經(jīng)常要用到簡化鐵碳狀態(tài)圖.Thoseportionsoftheiron-carbondiagramnearthedeltaregionandthoseabove2%carboncontentareoflittleimportancetotheengineerandaredeleted.Asimplifieddiagram,suchastheoneinFig.2.1,focusesontheeutectoidregionandisquiteusefulinunderstandingthepropertiesandprocessingofsteel.鐵碳狀態(tài)圖中靠近三角區(qū)和含碳量高于2%的那些部分對工程師而言不重要,因此將它們刪除.如圖2.1所示的簡化鐵碳狀態(tài)圖將焦點集中在共析區(qū),這對理解鋼的性能和處理是十分有用的.Thekeytransitiondescribedinthisdiagramisthedecompositionofsingle-phaseaustenite<γ>tothetwo-phaseferritepluscarbidestructureastemperaturedrops.在此圖中描述的關鍵轉變是單相奧氏體<γ>隨著溫度下降分解成兩相鐵素體加滲碳體組織結構.Controlofthisreaction,whicharisesduetothedrasticallydifferentcarbonsolubilityofausteniteandferrite,enablesawiderangeofpropertiestobeachievedthroughheattreatment.控制這一由于奧氏體和鐵素體的碳溶解性完全不同而產(chǎn)生的反應,使得通過熱處理能獲得很大范圍的特性.Tobegintounderstandtheseprocesses,considerasteeloftheeutectoidcomposition,0.77%carbon,beingslowcooledalonglinex-x’inFig.2.1.Attheuppertemperatures,onlyausteniteispresent,the0.77%carbonbeingdissolvedinsolidsolutionwiththeiron.Whenthesteelcoolsto727℃<1341℉>,severalchangesoccursimultaneously.為了理解這些過程,考慮含碳量為0.77%的共析鋼,沿著圖2.1的x-x’線慢慢冷卻.在較高溫度時,只存在奧氏體,0.77%的碳溶解在鐵里形成固溶體.當鋼冷卻到727℃<1341℉>時,將同時發(fā)生若干變化.TheironwantstochangefromtheFCCaustenitestructuretotheBCCferritestructure,buttheferritecanonlycontain0.02%carboninsolidsolution.鐵需要從面心立方體奧氏體結構轉變?yōu)轶w心立方體鐵素體結構,但是鐵素體只能容納固溶體狀態(tài)的0.02%的碳.Therejectedcarbonformsthecarbon-richcementiteintermetallicwithcompositionFe3C.Inessence,thenetreactionattheeutectoidisaustenite0.77%C→ferrite0.02%C+cementite6.67%C.被析出的碳與金屬化合物Fe3C形成富碳的滲碳體.本質上,共析體的基本反應是奧氏體0.77%的碳→鐵素體0.02%的碳+滲碳體6.67%的碳.Sincethischemicalseparationofthecarboncomponentoccursentirelyinthesolidstate,theresultingstructureisafinemechanicalmixtureofferriteandcementite.Specimenspreparedbypolishingandetchinginaweaksolutionofnitricacidandalcoholrevealthelamellarstructureofalternatingplatesthatformsonslowcooling.由于這種碳成分的化學分離完全發(fā)生在固態(tài)中,產(chǎn)生的組織結構是一種細致的鐵素體與滲碳體的機械混合物.通過打磨并在弱硝酸酒精溶液中蝕刻制備的樣本顯示出由緩慢冷卻形成的交互層狀的薄片結構.Thisstructureiscomposedoftwodistinctphases,buthasitsownsetofcharacteristicpropertiesandgoesbythenamepearlite,becauseofitsresemblancetomother-of-pearlatlowmagnification.這種結構由兩種截然不同的狀態(tài)組成,但它本身具有一系列特性,且因與低倍數(shù)放大時的珠母層有類同之處而被稱為珠光體.Steelshavinglessthantheeutectoidamountofcarbon<lessthan0.77%>areknownashypo-eutectoidsteels.Considernowthetransformationofsuchamaterialrepresentedbycoolingalongliney-y’inFig.2.1.含碳量少于共析體<低于0.77%>的鋼稱為亞共析鋼.現(xiàn)在來看這種材料沿著圖2.1中y-y’線冷卻的轉變情況.Athightemperatures,thematerialisentirelyaustenite,butuponcoolingentersaregionwherethestablephasesareferriteandaustenite.Tie-lineandlevel-lawcalculationsshowthatlow-carbonferritenucleatesandgrows,leavingtheremainingaustenitericherincarbon.在較高溫度時,這種材料全部是奧氏體,但隨著冷卻就進入到鐵素體和奧氏體穩(wěn)定狀態(tài)的區(qū)域.由截線及杠桿定律分析可知,低碳鐵素體成核并長大,剩下含碳量高的奧氏體.At727℃<1341℉>,theausteniteisofeutectoidcomposition<0.77%carbon>andfurthercoolingtransformstheremainingaustenitetopearlite.Theresultingstructureisamixtureofprimaryorpro-eutectoidferrite<ferritethatformedabovetheeutectoidreaction>andregionsofpearlite.在727℃<1341℉>時,奧氏體為共析組成<含碳量0.77%>,再冷卻剩余的奧氏體就轉化為珠光體.作為結果的組織結構是初步的共析鐵素體<在共析反應前的鐵素體>和部分珠光體的混合物.Hypereutectoidsteelsaresteelsthatcontaingreaterthantheeutectoidamountofcarbon.Whensuchsteelcools,asshowninz-z’ofFig.2.1theprocessissimilartothehypo-eutectoidcase,exceptthattheprimaryorpro-eutectoidphaseisnowcementiteinsteadofferrite.過共析鋼是含碳量大于共析量的鋼.當這種鋼冷卻時,就像圖2.1的z-z’線所示,除了初步的共析狀態(tài)用滲碳體取代鐵素體外,其余類似亞共析鋼的情況.Asthecarbon-richphaseforms,theremainingaustenitedecreasesincarboncontent,reachingtheeutectoidcompositionat727℃<1341℉>.Asbefore,anyremainingaustenitetransformstopearliteuponslowcoolingthroughthistemperature.隨著富碳部分的形成,剩余奧氏體含碳量減少,在727℃<1341℉>時達到共析組織.就像以前說的一樣,當緩慢冷卻到這溫度時所有剩余奧氏體轉化為珠光體.Itshouldberememberedthatthetransitionsthathavebeendescribedbythephasediagramsareforequilibriumconditions,whichcanbeapproximatedbyslowcooling.Withslowheating,thesetransitionsoccurinthereversemanner.應該記住由狀態(tài)圖描述的這種轉化只適合于通過緩慢冷卻的近似平衡條件.如果緩慢加熱,則以相反的方式發(fā)生這種轉化.However,whenalloysarecooledrapidly,entirelydifferentresultsmaybeobtained,becausesufficienttimeisnotprovidedforthenormalphasereactionstooccur,insuchcases,thephasediagramisnolongerausefultoolforengineeringanalysis.

然而,當快速冷卻合金時,可能得到完全不同的結果.因為沒有足夠的時間讓正常的狀態(tài)反應發(fā)生,在這種情況下對工程分析而言狀態(tài)圖不再是有用的工具.? Hardening淬火Hardeningistheprocessofheatingapieceofsteeltoatemperaturewithinoraboveitscriticalrangeandthencoolingitrapidly.淬火就是把鋼件加熱到或超過它的臨界溫度范圍,然后使其快速冷卻的過程.Ifthecarboncontentofthesteelisknown,thepropertemperaturetowhichthesteelshouldbeheatedmaybeobtainedbyreferencetotheiron-ironcarbidephasediagram.However,ifthecompositionofthesteelisunknown,alittlepreliminaryexperimentationmaybenecessarytodeterminetherange.如果鋼的含碳量已知,鋼件合適的加熱溫度可參考鐵碳合金狀態(tài)圖得到.然而當鋼的成分不知道時,則需做一些預備試驗來確定其溫度范圍.Agoodproceduretofollowistoheat-quenchanumberofsmallspecimensofthesteelatvarioustemperaturesandobservetheresult,eitherbyhardnesstestingorbymicroscopicexamination.Whenthecorrecttemperatureisobtained,therewillbeamarkedchangeinhardnessandotherproperties.要遵循的合適步驟是將這種鋼的一些小試件加熱到不同的溫度后淬火,再通過硬度試驗或顯微鏡檢查觀測結果.一旦獲得正確的溫度,硬度和其它性能都將有明顯的變化.Inanyheat-treatingoperationtherateofheatingisimportant.Heatflowsfromtheexteriortotheinteriorofsteelatadefiniterate.Ifthesteelisheatedtoofast,theoutsidebecomeshotterthantheinterioranduniformstructurecannotbeobtained.在任何熱處理作業(yè)中,加熱的速率都是重要的.熱量以一定的速率從鋼的外部傳導到內部.如果鋼被加熱得太快,其外部比內部熱就不能得到均勻的組織結構.Ifapieceisirregularinshape,aslowrateisallthemoreessentialtoeliminatewarpingandcracking.Theheavierthesection,thelongermustbetheheatingtimetoachieveuniformresults.如果工件形狀不規(guī)則,為了消除翹曲和開裂最根本的是加熱速率要緩慢.截面越厚,加熱的時間就要越長才能達到均勻的結果.Evenafterthecorrecttemperaturehasbeenreached,thepieceshouldbeheldatthattemperatureforasufficientperiodoftimetopermititsthickestsectiontoattainauniformtemperature.即使加熱到正確的溫度后,工件也應在此溫度下保持足夠時間以讓其最厚截面達到相同溫度.Thehardnessobtainedfromagiventreatmentdependsonthequenchingrate,thecarboncontent,andtheworksize.Inalloysteelsthekindandamountofalloyingelementinfluencesonlythehardenability<theabilityoftheworkpiecetobehardenedtodepths>ofthesteelanddoesnotaffectthehardnessexceptinunhardenedorpartiallyhardenedsteels.通過給定的熱處理所得到的硬度取決于淬火速率、含碳量和工件尺寸.除了非淬硬鋼或部分淬硬鋼外,合金鋼中合金元素的種類及含量僅影響鋼的淬透性<工件被硬化到深層的能力>而不影響硬度.Steelwithlowcarboncontentwillnotrespondappreciablytohardeningtreatment.Asthecarboncontentinsteelincreasesuptoaround0.60%,thepossiblehardnessobtainablealsoincreases.含碳量低的鋼對淬火處理沒有明顯的反應.隨著鋼的含碳量增加到大約0.60%,可能得到的硬度也增加.Abovethispointthehardnesscanbeincreasedonlyslightly,becausesteelsabovetheeutectoidpointaremadeupentirelyofpearliteandcementiteintheannealedstate.Pearliterespondsbesttoheat-treatingoperations;andsteelcomposedmostlyofpearlitecanbetransformedintoahardsteel.高于此點,由于超過共析點鋼完全由珠光體和退火狀態(tài)的滲碳體組成,硬度增加并不多.珠光體對熱處理作業(yè)響應最好；基本由珠光體組成的鋼能轉化成硬質鋼.Asthesizeofpartstobehardenedincreases,thesurfacehardnessdecreasessomewhateventhoughallotherconditionshaveremainedthesame.Thereisalimittotherateofheatflowthroughsteel.即使所有其它條件保持不變,隨著要淬火的零件尺寸的增加其表面硬度也會有所下降.熱量在鋼中的傳導速率是有限的.Nomatterhowcoolthequenchingmediummaybe,iftheheatinsidealargepiececannotescapefasterthanacertaincriticalrate,thereisadefinitelimittotheinsidehardness.However,brineorwaterquenchingiscapableofrapidlybringingthesurfaceofthequenchedparttoitsowntemperatureandmaintainingitatorclosetothistemperature.無論淬火介質怎么冷,如果在大工件中的熱量不能比特定的臨界速率更快散發(fā),那它內部硬度就會受到明確限制.然而鹽水或水淬火能夠將被淬零件的表面迅速冷卻至本身溫度并將其保持或接近此溫度.Underthesecircumstancestherewouldalwaysbesomefinitedepthofsurfacehardeningregardlessofsize.Thisisnottrueinoilquenching,whenthesurfacetemperaturemaybehighduringthecriticalstagesofquenching.在這種情況下不管零件尺寸如何,其表面總歸有一定深度被硬化.但油淬情況就不是如此,因為油淬時在淬火臨界階段零件表面的溫度可能仍然很高.? Tempering回火Steelthathasbeenhardenedbyrapidquenchingisbrittleandnotsuitableformostuses.Bytemperingordrawing,thehardnessandbrittlenessmaybereducedtothedesiredpointforserviceconditions．快速淬火硬化的鋼是硬而易碎的,不適合大多數(shù)場合使用.通過回火,硬度和脆性可以降低到使用條件所需要的程度.Asthesepropertiesarereducedthereisalsoadecreaseintensilestrengthandanincreaseintheductilityandtoughnessofthesteel.Theoperationconsistsofreheatingquench-hardenedsteeltosometemperaturebelowthecriticalrangefollowedbyanyrateofcooling.隨著這些性能的降低,拉伸強度也降低而鋼的延展性和韌性則會提高.回火作業(yè)包括將淬硬鋼重新加熱到低于臨界范圍的某一溫度然后以任意速率冷卻.Althoughthisprocesssoftenssteel,itdiffersconsiderablyfromannealinginthattheprocesslendsitselftoclosecontrolofthephysicalpropertiesandinmostcasesdoesnotsoftenthesteeltotheextentthatannealingwould.Thefinalstructureobtainedfromtemperingafullyhardenedsteeliscalledtemperedmartensite.雖然這過程使鋼軟化,但它與退火是大不相同的,因為回火適合于嚴格控制物理性能并在大多數(shù)情況下不會把鋼軟化到退火那種程度.回火完全淬硬鋼得到的最終組織結構被稱為回火馬氏體.Temperingispossiblebecauseoftheinstabilityofthemartensite,theprincipalconstituentofhardenedsteel.Low-temperaturedraws,from300℉to400℉<150℃~205℃>,donotcausemuchdecreaseinhardnessandareusedprincipallytorelieveinternalstrains.由于馬氏體這一淬硬鋼主要成分的不穩(wěn)定性,使得回火成為可能.低溫回火,300℉到400℉<150℃~205℃>,不會引起硬度下降很多,主要用于減少內部應變.Asthetemperingtemperaturesareincreased,thebreakdownofthemartensitetakesplaceatafasterrate,andatabout600℉<315℃>thechangetoastructurecalledtemperedmartensiteisveryrapid.Thetemperingoperationmaybedescribedasoneofprecipitationandagglomerationorcoalescenceofcementite.隨著回火溫度的提高,馬氏體以較快的速率分解,并在大約600℉<315℃>迅速轉變?yōu)楸环Q為回火馬氏體的結構.回火作業(yè)可以描述為滲碳體析出和凝聚或聚結的過程.Asubstantialprecipitationofcementitebeginsat600℉<315℃>,whichproducesadecreaseinhardness.Increasingthetemperaturecausescoalescenceofthecarbideswithcontinueddecreaseinhardness.滲碳體的大量析出開始于600℉<315℃>,這使硬度下降.溫度的上升會使碳化物聚結而硬度繼續(xù)降低.Intheprocessoftempering,someconsiderationshouldbegiventotimeaswellastotemperature.Althoughmostofthesofteningactionoccursinthefirstfewminutesafterthetemperatureisreached,thereissomeadditionalreductioninhardnessifthetemperatu