金属热处理外文文献及翻译Word文件下载.docx
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金属热处理外文文献及翻译Word文件下载.docx
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”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.
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.
Insomeinstances,heattreatmentproceduresareclear—cutintermsoftechniqueandapplication.whereasinotherinstances,descriptionsorsimpleexplanationsareinsufficientbecausethesametechniquefrequentlymaybeusedtoobtaindifferentobjectives.Forexample,stressrelievingandtemperingareoftenaccomplishedwiththesameequipmentandbyuseofidenticaltimeandtemperaturecycles.Theobjectives,however,aredifferentforthetwoprocesses.
For28℃to56℃)aboveitsspecificuppertransformationtemperature.Thisisfollowedbycoolinginstillairtoatleastsometemperaturewellbelowitstransformationtemperaturerange.Forlow—carbonsteels,theresultingstructureandpropertiesarethesameasthoseachievedbyfullannealing;
Thenormalizingprocessusuallyis
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