国外热处理教程WORD版

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1、ME318ManufacturingTechniquesHeatTreatmentOBJECT:ToperformaJominyend-quenchtestinordertoobserveheattreatmenthardeningandpreparethehardenabilitycurveforasteelbar.THEORY:Steelisthemostimportantengineeringandconstructionmaterial;itaccountsforapproximately80%ofallmetalsproduced.S

2、teelhasattainedthisdegreeofprominencebecauseitcombinesstrength,easeoffabricabilityintomanyshapes,andawiderangeofpropertiesalongwithlowcost.Alsoitispossibletogiveawiderangeofmechanicalpropertiestosteelsbychangingthesizeadshapeofthegrainsorchangingitsmicroconstituents.Thisprop

3、ertyowestoseveraldifferentwaysthataustenitecandecompose.Fundamentally,allsteelsarealloysofironandcarbon.So-calledplaincarbonsteelsalsogenerallyhavesmallbutspecifiedamountsofphosphorusandsulfur.Alloysteelsarethosewhichcontainspecifiedpercentagesofotherelementsintheirchemicalc

4、ompositions.12ME318ManufacturingTechniquesFigure1.Iron-CarbonEquilibriumDiagram[1]HARDENABILITY:Ingeneralstrengthofagivensteelisproportionaltoitshardness;thehigherthehardness,thestrongerthesteel.Thecarboncontentofasteeldeterminesthe12ME318ManufacturingTechniquesmaximumhardne

5、ssattainable.Themostimportantfactorinfluencingthemaximumhardnessismassofthemetalbeingquenched.Inasmallsection,theheatisextractedquickly,thusexceedingthecriticalcoolingrateofthespecificsteel.Thecriticalcoolingrateisthatrateofcoolingwhichmustbeexceededtopreventformationofnon-m

6、artensiteproducts.Hardenabilityistheeasewithwhichhardnessmaybeattained.Asteelthattransformsrapidlyfromaustenitetoferritepluscarbidehaslowhardenabilitybecause(a+carbide)isformedattheexpenseofmartensite.Converselyasteelthattransformsslowlyfromaustenitetoferritehasgreaterharden

7、ability.Foranygivensteel,thereisadirectandconsistentrelationshipbetweenhardnessandcoolingrate.Howevertherelationshipishighlynon-linear.Thereisastandardizedtestthatletsusmakenecessarypredictionsofhardness.ThisistheJominyend-quenchedtest.Aroundbarwithastandardsizeisheatedtofor

8、mausteniteandisthanend-quenchedwithawaterstreamofspecifiedflowrateandpressu