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1、外文翻译原文：HeatTreatmentTheunderstandingofheattreatmentisembracedbythebroaderstudyofmetallurgy.Metallurgyisthephysics,chemistry,andengineeringrelatedtometalsfromoreextractiontothefinalproduct.Heattreatmentistheoperationofheatingandcoolingametalinitssolidstatetochangeitsp
2、hysicalproperties.Accordingtotheprocedureused,steelcanbehardenedtoresistcuttingactionandabrasion,oritcanbesoftenedtopermitmachining.Withtheproperheattreatmentinternalstressesmayberemoved,grainsizereduced,toughnessincreased,orahardsurfaceproducedonaductileinterior.The
3、analysisofthesteelmustbeknownbecausesmallpercentagesofcertainelements,notablycarbon,greatlyaffectthephysicalproperties.Alloysteelowetheirpropertiestothepresenceofoneormoreelementsotherthancarbon,namelynickel,chromium,manganese,molybdenum,tungsten,silicon,vanadium,and
4、copper.Becauseoftheirimprovedphysicalpropertiestheyareusedcommerciallyinmanywaysnotpossiblewithcarbonsteels.Thefollowingdiscussionappliesprincipallytotheheattreatmentofordinarycommercialsteelsknownasplaincarbonsteels.Withthisprocesstherateofcoolingisthecontrollingfac
5、tor,rapidcoolingfromabovethecriticalrangeresultsinhardstructure,whereasveryslowcoolingproducestheoppositeeffect.Ifwefocusonlyonthematerialsnormallyknownassteels,asimplifieddiagramisoftenused.Thoseportionsoftheiron-carbondiagramnearthedeltaregionandthoseabove2%carbonc
6、ontentareoflittleimportancetotheengineerandaredeleted.Asimplifieddiagram,suchastheoneinFig.2.1,focusesontheeutectoidregionandisquiteusefulinunderstandingthepropertiesandprocessingofsteel.Thekeytransitiondescribedinthisdiagramisthedecompositionofsingle-phaseaustenite(
7、γ)tothetwo-phaseferritepluscarbidestructureastemperaturedrops.Controlofthisreaction,whicharisesduetothedrasticallydifferentcarbonsolubilityofausteniteandferrite,enablesawiderangeofpropertiestobeachievedthroughheattreatment.Tobegintounderstandtheseprocesses,consideras
8、teeloftheeutectoidcomposition,0.77%carbon,beingslowcooledalonglinex-x’inFig.2.1.Attheuppertemperatures,onlyausteniteispresent,the0.
