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1、外文翻译原文：HeatTreatmentTheunderstandingofheattreatmentisembracedbythebroaderstudyofmetallurgy.Metallurgyisthephysics,chemistry,andengineeringrelatedtometalsfromoreextractiontothefinalproduct.Heattreatmentistheoperationofheatingandcoolingametalinitssolidstat
2、etochangeitsphysicalproperties・Accordingtotheprocedureused,steelcanbehardenedtoresistcuttingactionandabrasion,oritcanbesoftenedtopermitmachining.Withtheproperheattreatmentinternalstressesmayberemoved,grainsizereduced,toughnessincreased,orahardsurfaceprod
3、ucedonaductileinterio匚Theanalysisofthesteelmustbeknownbecausesmallpercentagesofcertainelements,notablycarbon,greatlyaffectthephysicalproperties・Alloysteelowetheirpropertiestothepresenceofoneormoreelementsotherthancarbon,namelynickelchromium,manganese,mol
4、ybdenum,tungsten,silicon,vanadium,andcopper.Becauseoftheirimprovedphysicalpropertiestheyareusedcommerciallyinmanywaysnotpossiblewithcarbonsteels.Thefollowingdiscussionappliesprincipallytotheheattreatmentofordinarycommercialsteelsknownasplaincarbonsteels.
5、Withthisprocesstherateofcoolingisthecontrollingfactor,rapidcoolingfromabovethecriticalrangeresultsinhardstructure,whereasveryslowcoolingproducestheoppositeeffect・Ifwefocusonlyonthematerialsnormallyknownassteels,asimplifieddiagramisoftenused.Thoseportions
6、oftheiron-carbondiagramnearthedeltaregionandthoseabove2%carboncontentareoflittleimportancetotheengineerandaredeleted.Asimplifieddiagram,suchastheoneinFig.2.1,focusesontheeutectoidregionandisquiteusefulinunderstandingthepropertiesandprocessingofsteel・Thek
7、eytransitiondescribedinthisdiagramisthedecompositionofsingle-phaseaustenite(y)tothetwo-phaseferritepluscarbidestnictureastemperaturedrops・Controlofthisreaction,whicharisesduetothedrasticallydifferentcarbonsolubilityofausteniteandferrite,enablesawiderange
8、ofpropertiestobeachievedthroughheattreatment.Tobegintounderstandtheseprocesses,considerasteeloftheeutectoidcomposition,0.77%carbon,beingslowcooledalonglinex・x，inFig.2.1.Attheuppertemperatures,onlyausteniteispresent,the0.77
