金属热处理外文及翻译.docx

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