【模具與數(shù)控專業(yè)英語】教學(xué)內(nèi)容1103

UnitOneTheDie&MoldMaterialsandHeatTreatment模具與數(shù)控專業(yè)英語11.3HeatTreatmentofDie&MoldMaterials

模具與數(shù)控專業(yè)英語1.3.1ThePurposesofHeatTreatmentThemainpurposeofheattreatmentfordie-makingandmold-makingmaterialsistocontrolthepropertiesofaspecificmetaloralloythroughthealterationofthestructureofthespecificmetaloralloybyheatingittodefinitetemperaturesandcoolingatvariousrates．Thiscombinationofheatingandcontrolledcoolingdeterminesnotonlythenatureanddistributionofthemicroconstituents，whichinturndeterminetheproperties，butalsothegrainsize［2］.2模具與數(shù)控專業(yè)英語Heattreatingshouldimprovethealloyormetalfortheserviceintended．Someofvariouspurposesofheattreatingareasfollows：l.Toremovestrainsaftercoldworkingsuchasforging,rolling.2.Toremoveinternalstressessuchasproducedbydrawing,bending,extrudingorwelding.3.Toincreasethehardnessofthematerialandwear-resistingproperties.3模具與數(shù)控專業(yè)英語4.Toimprovemachinability.5.Toimprovethecomprehensiveperformanceofmaterialonpurpose,suchasnormalizing.6.Tosoftenthematerial，asinannealing.7.Toimproveorchangepropertiesofamaterialsuchascorrosionresistance，heatresistance，orothersasrequired.4模具與數(shù)控專業(yè)英語1.3.2TypesofHeatTreatmentHeattreatmentofferrousmaterialsinvolvesseveralimportantoperationswhicharecustomarilyreferredtoundervariousheadings,suchasannealing,normalizing,tempering,hardening,casehardening,spheroidizing,stressrelieving,surfacetreatmentsandsoon.

Annealing---Theprocessofannealingconsistsofheatingthesteeltoanelevatedtemperatureforadefiniteperiodoftimeand，usually，coolingitslowly．

5模具與數(shù)控專業(yè)英語Annealingisdonetoproducehomogenizationandtoestablishnormalequilibriumconditions，withcorrespondingcharacteristicproperties．Inviewthatdieandmoldsteelisgenerallypurchasedintheannealedcondition,sometimesitisnecessarytoreworkadieormoldthathasbeenhardened，andthedieormoldmustthenbeannealed．Forthistypeofanneal,thesteelisheatedslightlyaboveitscriticalrangeandthencooledveryslowly.6模具與數(shù)控專業(yè)英語

Normalizing---Involvesheatingthematerialtoatemperatureofabout55～100℃abovethecriticalrangeandcoolinginstillair．Thisisabout55℃overtheregularhardeningtemperature．Thepurposeofnormalizingisusuallytorefinegrainstructuresthathavebeencoarsenedinforging．Withmostofthemedium－carbonforgingsteels，alloy，normalizingishighlyrecommendedafterforgingandbeforemachiningtoproducemorehomogeneousstructures，andinmostcases，improvedmachinability［3］.7模具與數(shù)控專業(yè)英語High－alloyair－h(huán)ardenedsteelsarenevernormalized，sincetodosowouldcausethemtohardenanddefeattheprimarypurpose．

Tempering---Thisistheprocessofheatingquenchedandhardenedsteelsandalloystosometemperaturebelowthelowercriticaltemperaturetoreduceinternalstressessetupinhardening．

Hardening---Thisistheprocessofheatingtoatemperatureabovethecriticalrange,andcoolingrapidlyenoughthroughthecriticalrangetoreducetoappreciablyhardenthesteel．8模具與數(shù)控專業(yè)英語

CaseHardening---Theadditionofcarbontothesurfaceofsteelpartsandthesubsequenthardeningoperationsareimportantphasesinheattreating．Theprocessmayinvolvetheuseofmoltensodiumcyanidemixtures，packcarburizingwithactivatedsolidmaterialsuchascharcoalorcoke,gasoroilcarburizing,anddrycyaniding．9模具與數(shù)控專業(yè)英語

Spheroidizing--isaformofannealingwhich，intheprocessofheatingandcoolingsteel，producesaroundedorglobularformofcarbide—thehardconstituentinsteel．Steelsarenormallyspheroidizedtoimprovemachinability.Thisisaccomplishedbyheatingtoatemperatureto749～760℃forcarbonsteelsandhigherformanyalloytoolsteels，holdingatheatonetofourhours，andcoolingslowlyinthefurnace.10模具與數(shù)控專業(yè)英語

Stress

Relieving--Thisisamethodofrelievingtheinternalstressessetupinsteelduringforming，coldworking，andcoolingafterweldingormachining．Itisthesimplestheattreatmentandisaccomplishedmerelybyheatingto649～732℃followedbyairorfurnacecooling．Largediesareusuallyroughedout，thenstress－relievedandfinish－machined．Thiswillminimizechangeofshapenotonlyduringmachiningbutduringsubsequentheattreatingaswell．11模具與數(shù)控專業(yè)英語Weldedsectionswillalsohavelocked－instressesowingtoacombinationofdifferentialheatingandcoolingcyclesaswellastochangesincrosssection．Suchstresseswillconsiderablemovementinmachiningoperations．12模具與數(shù)控專業(yè)英語

Surface

Treatments---Duringthepast20years，severalprocesseshavebeenintroducedtoobtainenhancedsurfacehardnessofsteels．Someofthemhavedevelopedfromcasecarburizingand

nitriding，toobtainfasterprocessingtimeswithbetterenvironmentalcontrolofandimprovedproperties．Varioussaltbathprocesseshavebeenusedandnowawiderangeofnewmethodsisavailable．13模具與數(shù)控專業(yè)英語Inthediecastingindustrysurfacetreatmentsareappliedtosteelstoimprovethepropertiesofnozzles，ejectorpins,coresandshotsleeves，toprovidemaximumresistancetoerosion，pittingandsoldering．Treatmentofdiecavitieshasreceivedonlylimited“acclaim，becausethecomplexthermalpatterns