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1、机械制造专业英语毕业考核任课老师：吴海生班级：机制11302姓名：孙康学号：11022654ReadingComprehension(1)HeatTreatmentofDieSteelsAlthoughalloysteelscontainelementssuchaschromium,molybdenumandvanadium・Twoconstituentsareessentialforheattreatment:iron,termedferriteinmetallography,andcarbon,whichcombineswithi
2、rontoformcementite,thehardintermetalliccompoundFe3C・Thesetwoconstituentsformaeutectoidstructureknownaspearlitewhenthesteeliscooledslowlyenoughtoreachequilibrium,butbyrapidcoolingthesteelishardened.Whensuchaquenchedsteelistempered,structureswithmechanicalpropertiesinterm
3、ediatebetweenthoseoftheslowlycooledandthequenchedconditionsareformed.Inrecentyearstherehasbeenagreaterunderstandingofthecomplexstructuralchangestakingplaceduringheattreatment,withthehelpofphasetransformationdiagrams.Useofthesediagramscanleadtobettercontroloftheheattreat
4、mentcyclewhichinturnwillensurethatoptimumpropertiesandmaximumdielifeareachieved.SurfaceTreatmentsforSteelsDuringthepast20years,severalprocesseshavebeenintroducedtoobtainenhancedsurfacehardnessofsteels.Someofthemhavedevelopedfromcasecarburizingandnitriding,toobtainshorte
5、rprocessingtimeswithbetterenvironmentalcontrolandimprovedproperties・Varioussaltbathprocesseshavebeenusedandnowawiderangeofnewmethodsisavailable.Inthediecastingindustrysurfacetreatmentsareappliedtosteelstoimprovethepropertiesofnozzles,ejectorpins,coresandshotsleeves,topr
6、ovidemaximumresistancetoerosion,pittingandsoldering..Treatmentofdiecavitieshasreceivedonlylimitedacclaim,becausethecomplexthermalpattern,producedonlargediecomponentsleadtostresseswhicharesufficientlyhightobreakthroughthethinsurfacetreatedlayers,leadingtoprematurefailure
7、.Experienceindropforginghasalsoindicatedthatsurfacetreatmentsoftheirdieshavenotbeenparticularlysuccessful.Thermochemicaltreatmentsarcappliedtodiecastingdiecomponents;thesurfacechemistryofthesteelismodifiedbytheintroductionofrdtrogen,carbonandsometimesotherelements;thepr
8、ocessesareoi‘themaintypeslistAlthoughalloysteelscontainelementssuchaschromium,molybdenumandvanadium・Twoconstit
