过程装备与控制工程专业专业英语翻译9-豆柴文库

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过程装备与控制工程专业专业英语翻译9

第一篇：过程装备与控制工程专业专业英语翻译9ReadingMaterial9HeatTreatmentofSteelTypesofHeatTreatingOperationsFiveoperationsaredetailedinthislessonasthebasisofheattreatment.ExplanationsoftheseOperationsfollow.StressRelievingWhenametalIsheated，expansionoccurswhichismoreorlessproportionaltothetemperaturerise.Uponcoolingametal,thereversereactiontakesplace.Thatis,acontractionisobserved．Whenasteelbarorplateisheatedatonepointmorethanatanother，asinweldingorduringforging，Internalstressesaresetup．Duringheating,expansionoftheheatedareacannottakeplaceunhindered，andittendstodeform．Oncooling，contractionispreventedfromtakingplacebytheunyieldingcoldmetalsurroundingtheheatedarea．Theforcesattemptingtocontractthemetalarenotrelieved，andwhenthemetaliscoldagain，theforcesremainasinternalstresses．stressesalsoresultfromvolumechanges,whichaccompanymetaltransformationsandprecipitation．Internalorresidualstressesarebadbecausetheymaycausewarpingofsteelpartswhentheyaremachined．To0relievethesestresses，steelisheatedtoaround595C，assumingthattheentirepartisheateduniformly,thencooledslowlybacktoroomtemperature．Thisprocedureiscalledstressreliefannealing,ormerelystressrelieving.Becauseofcharacteristicsinherentincaststeel,thenormalizingtreatmentismorefrequentlyappliedtoingotspriortoworking，andtosteelcastingsandforgingspriortohardening.NormalizingTheprocessofnormalizingconsistsofheatingtoatemperatureabovethethirdtransformationtemperatureandallowingtheparttocoolinstillair.Theactualtemperaturerequiredforthisdependsonthecompositionofthesteel,0butisusuallyaround870C.Actually,thetermnormalizedoesnotdescribethepurpose.Theprocessmightbemoreaccuratelydescribedasahomogenizingorgrain-refiningtreatment.Withinanypieceofsteel,thecompositionisusuallynotuniformthroughout.Thatis,oneareamayhavemorecarbonthantheareaadjacenttoit.Thesecompositionaldifferencesaffectthewayinwhichthesteelwillrespondtoheattreatment.Ifitisheatedtoahightemperature,thecarboncanreadilydiffusethroughout,andtheresultisareasonablyuniformcompositionfromon