金属热处理外文及翻译.docx
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金属热处理外文及翻译.docx
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金属热处理外文及翻译
湖南工院
毕业设计(论文)外文翻译
外文题目
Heattreatmentofmetal
译文题目
金属热处理
系部
机械工程系
专业班级
机械设计制造及其自动化
学生姓名
指导教师
完成时间
原文
Heattreatmentofmetal
Thegenerallyaccepteddefinitionforheattreatingmetalsandmetalalloysis“heatingandcoolingasolidmetaloralloyinawaysoastoobtainspecificconditionsorproperties.”Heatingforthesolepurposeofhotworking(asinforgingoperations)isexcludedfromthisdefinition.Likewise,thetypesofheattreatmentthataresometimesusedforproductssuchasglassorplasticsarealsoexcludedfromcoveragebythisdefinition.
TransformationCurves
Thebasisforheattreatmentisthetime-temperature-transformationcurvesorTTTcurveswhere,inasinglediagramallthethreeparametersareplotted.Becauseoftheshapeofthecurves,theyarealsosometimescalledC-curvesorS-curves.
ToplotTTTcurves,theparticularsteelisheldatagiventemperatureandthestructureisexaminedatpredeterminedintervalstorecordtheamountoftransformationtakenplace.Itisknownthattheeutectoidsteel(T80)underequilibriumconditionscontains,allausteniteabove723℃,whereasbelow,itisthepearlite.Toformpearlite,thecarbonatomsshoulddiffusetoformcementite.Thediffusionbeingarateprocess,wouldrequiresufficienttimeforcompletetransformationofaustenitetopearlite.Fromdifferentsamples,itispossibletonotetheamountofthetransformationtakingplaceatanytemperature.Thesepointsarethenplottedonagraphwithtimeandtemperatureastheaxes.Throughthesepoints,transformationcurvescanbeplottedasshowninFig.1foreutectoidsteel.Thecurveatextremeleftrepresentsthetimerequiredforthetransformationofaustenitetopearlitetostartatanygiventemperature.Similarly,thecurveatextremerightrepresentsthetimerequiredforcompletingthetransformation.Betweenthetwocurvesarethepointsrepresentingpartialtransformation.ThehorizontallinesMsandMfrepresentthestartandfinishofmartensitictransformation.
ClassificationofHeatTreatingProcesses
Insomeinstances,heattreatmentproceduresareclear-cutintermsoftechniqueandapplication.whereasinotherinstances,descriptionsorsimpleexplanationsareinsufficientbecausethesametechniquefrequentlymaybeusedtoobtaindifferentobjectives.Forexample,stressrelievingandtemperingareoftenaccomplishedwiththesameequipmentandbyuseofidenticaltimeandtemperaturecycles.Theobjectives,however,aredifferentforthetwoprocesses.
Thefollowingdescriptionsoftheprincipalheattreatingprocessesaregenerallyarrangedaccordingtotheirinterrelationships.
Normalizingconsistsofheatingaferrousalloytoasuitabletemperature(usually50°Fto100°For28℃to56℃)aboveitsspecificuppertransformationtemperature.Thisisfollowedbycoolinginstillairtoatleastsometemperaturewellbelowitstransformationtemperaturerange.Forlow-carbonsteels,theresultingstructureandpropertiesarethesameasthoseachievedbyfullannealing;formostferrousalloys,normalizingandannealingarenotsynonymous.
Normalizingusuallyisusedasaconditioningtreatment,notablyforrefiningthegrainsofsteelsthathavebeensubjectedtohightemperaturesforforgingorotherhotworkingoperations.Thenormalizingprocessusuallyissucceededbyanotherheattreatingoperationsuchasaustenitizingforhardening,annealing,ortempering.
Annealingisagenerictermdenotingaheattreatmentthatconsistsofheatingtoandholdingatasuitabletemperaturefollowedbycoolingatasuitablerate.Itisusedprimarilytosoftenmetallicmaterials,butalsotosimultaneouslyproducedesiredchangesinotherpropertiesorinmicrostructure.Thepurposeofsuchchangesmaybe,butisnotconfinedto,improvementofmachinability,facilitationofcoldwork(knownasin-processannealing),improvementofmechanicalorelectricalproperties,ortoincreasedimensionalstability.Whenappliedsolelytorelivestresses,itcommonlyiscalledstress-reliefannealing,synonymouswithstressrelieving.
Whentheterm“annealing”isappliedtoferrousalloyswithoutqualification,fullannealingisapplied.Thisisachievedbyheatingabovethealloy’stransformationtemperature,thenapplyingacoolingcyclewhichprovidesmaximumsoftness.Thiscyclemayvarywidely,dependingoncompositionandcharacteristicsofthespecificalloy.
Quenchingisarapidcoolingofasteeloralloyfromtheaustenitizingtemperaturebyimmersingtheworkpieceinaliquidorgaseousmedium.Quenchingmediumcommonlyusedincludewater,5%brine,5%causticinanaqueoussolution,oil,polymersolutions,orgas(usuallyairornitrogen).
Selectionofaquenchingmediumdependslargelyonthehardenabilityofmaterialandthemassofthematerialbeingtreating(principallysectionthickness).
Thecoolingcapabilitiesoftheabove-listedquenchingmediavarygreatly.Inselectingaquenchingmedium,itisbesttoavoidasolutionthathasmorecoolingpowerthanisneededtoachievetheresults,thusminimizingthepossibilityofcrackingandwarpofthepartsbeingtreated.Modificationsofthetermquenchingincludedirectquenching,fogquenching,hotquenching,interruptedquenching,selectivequenching,sprayquenching,andtimequenching.
Tempering.Inheattreatingofferrousalloys,temperingconsistsofreheatingtheaustenitizedandquench-hardenedsteelorirontosomepreselectedtemperaturethatisbelowthelowertransformationtemperature(generallybelow1300℃or705℃).Temperingoffersameansofobtainingvariouscombinationsofmechanicalproperties.Temperingtemperaturesusedforhardenedsteelsareoftennohigherthan300℃(150℃).Theterm“tempering”shouldnotbeconfusedwitheitherprocessannealingorstressrelieving.Eventhoughtimeandtemperaturecyclesforthethreeprocessesmaybethesame,theconditionsofthematerialsbeingprocessedandtheobjectivesmaybedifferent.
Stressrelieving.Liketempering,stressrelievingisalwaysdonebyheatingtosometemperaturebelowthelowertransformationtemperatureforsteelsandirons.Fornonferrousmetals,thetemperaturemayvaryfromslightlyaboveroomtemperaturetoseveralhundreddegrees,dependingonthealloyandtheamountofstressreliefthatisdesired.
Theprimarypurposeofstressrelievingistorelievestressesthathavebeenimpartedtotheworkpiecefromsuchprocessesasforming,rolling,machiningorwelding.Theusualprocedureistoheatworkpiecetothepre-establishedtemperaturelongenoughtoreducetheresidualstresses(thisisatime-andtemperature-dependentoperation)toanacceptablelevel;thisisfollowedbycoolingatarelativelyslowratetoavoidcreationofnewstresses.
Thegenerallyaccepteddefinitionforheattreatingmetalsandmetalalloysis“heatingandcoolingasolidmetaloralloyinawaysoastoobtainspecificconditionsorproperties.”Heatingforthesolepurposeofhotworking(asinforgingoperations)isexcludedfromthisdefinition.Likewise,thetypesofheattreatmentthataresometimesusedforproductssuchasglassorplasticsarealsoexcludedfromcoveragebythisdefinition.
TransformationCurves
Thebasisforheattreatmentisthetime-temperature-transformationcurvesorTTTcurveswhere,inasinglediagramallthethreeparametersareplotted.Becauseoftheshapeofthecurves,theyarealsosometimescalledC-curvesorS-curves.
ToplotTTTcurves,theparticularsteelisheldatagiventemperatureandthestructureisexaminedatpredeterminedintervalstorecordtheamountoftransformationtakenplace.Itisknownthattheeutectoidsteel(T80)underequilibriumconditionscontains,allausteniteabove723℃,whereasbelow,itispearlite.Toformpearlite,thecarbonatomsshoulddiffusetoformcementite.Thediffusionbeingarateprocess,wouldrequiresufficienttimeforcompletetransformationofaustenitetopearlite.Fromdifferentsamples,itispossibletonotetheamountofthetransformationtakingplaceatanytemperature.Thesepointsarethenplottedonagraphwithtimeandtemperatureastheaxes.Throughthesepoints,transformationcurvescanbeplottedasshowninFig.1foreutectoidsteel.Thecurveatextremeleftrepresentsthetimerequiredforthetransformationofaustenitetopearlitetostartatanygiventemperature.Similarly,thecurveatextremerightrepresentsthetimerequiredforcompletingthetransformation.Betweenthetwocurvesarethepointsrepresentingpartialtransformation.ThehorizontallinesMsandMfrepresentthestartandfinishofmartensitictransformation.
ClassificationofHeatTreatingProcesses
Insomeinstances,heattreatmentproceduresareclear-cutintermsoftechniqueandapplication.whereasinotherinstances,descriptionsorsimpleexplanationsareinsufficientbecausethesametechniquefrequentlymaybeusedtoobtaindifferentobjectives.Forexample,stressrelievingandtemperingareoftenaccomplishedwiththesameequipmentandbyuseofidenticaltimeandtemperaturecycles.Theobjectives,however,aredifferentforthetwoprocesses.
Thefollowingdescriptionsoftheprincipalheattreatingprocessesaregenerallyarrangedaccordingtotheirinterrelationships.
Normalizingconsistsofheatingaferrousalloytoasuitabletemperature(usually50°Fto100°For28℃to56℃)aboveitsspecificuppertransformationtemperature.Thisisfollowedbycoolinginstillairtoatleastsometemperaturewellbelowitstransformationtemperaturerange.Forlow-carbonsteels,theresultingstructureandpropertiesarethesameasthoseachievedbyfullannealing;formostferrousalloys,normalizingandannealingarenotsynonymous.
Normalizingusuallyisusedasaconditioningtreatment,notablyforrefiningthegrains
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