外文翻译--普通碳素钢的淬火与回火.docVIP

1HardeningandTemperingofPlainCarbonSteelPlaincarbonsteelhasbeenvaluedfromearlytimebecauseofcertainproperties.thissoftsilver-graymetalcouldbeconvertedintoasuperhardsubstancethatwouldcutglassandmanyothersubstances，includingitselfwhensoft.Furthermore，itshardnesscouldbecontrolled.Thisconvertingofcarbonsteelintoasteelofusefulhardnessisdonewithdifferentheattreatments，twoofthemostimportantofwhicharehardeningandtempering(drawing)，whatstheplaincarbonsteelandwhichyouwillinvestigateinthislesson.PlainCarbonSteelInsimpleterms，aplaincarbonsteelmaybesaidtobeanalloyofironandcarboncontaininglessthan1.7%carbon.Inpractice，however，thesesteelsrarelycontainmorethanabout1.4%carbonandotherelementsarealsopresent，eitherasdeliberateadditions(e.g.manganese)orasimpurities(e.g.sulphurandphosphorus).Plaincarbonsteelsmaybeclassifiedintothreemaingroups:1.Lowcarbonsteel(mildsteel)containinglessthan0.3%carbon.2.Mediumcarbonsteelcontaining0.3%to0.6%carbon.3.Highcarbonsteelcontaining0.6%to1.4%carbon.LowcarbonsteelLowcarbonsteelsmaybesub-dividedinto:1.Deadmildsteelcontaining0.05%to0.10%carbonInthemanufactureofthismaterial，completedeoxidationisnotcarriedoutanditismadeasrimmingsteel.Itisproducedashotandcoldworkedsheet，strip，rod，wireandtube，andisavailableinthehot-workedorprocessannealedconditionforthedeepdrawingofsheet，butthestrengthislow.Thistypeofsteelisusedforthemanufactureofmotorcarbodies，refrigerators，washingmachines，officefurniture，pressings，rivetsandnails.2.Carburisingsteelscontaining0.1%to0.2%carbonThestrengthandhardnessofthesesteelsislow，butahardsurfacecanbeobtainedbycarburizinginordertocombineawear-resistantsurfacewithtoughcoreproperties.TheductilitymakesrapidmachiningdifficultunlesstheMnandScontentisincreasedby2usingashlphurcontentof0.2%to0.3%withabout1%manganese.3.Constructionalmildsteelscontaining0.2%to0.3%carbonAsthecarboncontentisraisedabove0.2%，thestrengthincreasesintotherangerequiredforconstructionalpurposes，buttheductilitydecreases.Thefabricationqualities(workingandweldingcharacteristics)ofthismaterialareverygood.Thesteelishot-rolledintoplateformakingboilers，shipsandvehicles，andalsointosections(e.g.girders，beams，joists)foruseinbridgesandbuildings.Thesteelisoftenusedinthehot-rolledcondition，butthesmallersizedmaterialmaybenormalized.Ithasbeenestimatedthatabout90%(byweight)ofallsteelusedisofthislowcarbonclassification.MediumCarbonSteelsMediumcarbonsteelsareoftenquenched-hardenedandfullytemperedtogivegoodstrengthwithmaximumtoughness,whicharethepropertiesrequiredofcomponentssuchasshafts,gearsandconnectingrods.Steelscontaining0.4%to0.5%carbonmayalsobesurfacehardenedbylocalizedheatingandquenching.HighCarbonSteelHighcarbonsteelarequenchhardenedandlightlytemperedtogivehighhardnesswithonlylimitedtoughness.Materialinthisclassificationismainlyusedformakingfairlysmall,relativelyinexpensivecuttingtoolssothatthegroupasawholeisknownascarbontoolsteel.Steelscontaining0.6%to0.8%carbonareusedformakingdies,springs,wireropesandrailwaytypes.Manydifferentkindsoftoolsaremadeformhighercarbonsteelsasindicatedbelow.Carbon%Typeoftool0.81.0Coldchisels,shearblades,punches,hammers1.01.2Files,axes,saws,knives1.21.4Razors,drills,wood-cuttingandmetal-cuttingtoolsLimitationsofPlainCarbonSteelsPlaincarbonsteelshavemanylimitationsincludingthefollowing:(1)Ifreasonabletoughnessandductilityarerequired,themaximumtensilestrengthobtainableisabout700N/2mm.3(2)Largesectionscannotbeeffectivelyhardened,thusrestrictingtheirusetorelativelythinsections.(3)Waterquenchingisnecessaryforfullhardeningwithconsequentriskofdistortionandcracking.(4)Rapidsofteningaboveabout300Climitstheiruseforhigh-speedmetalcutting.(5)Poorresistancetocorrosionandtooxidationatelevatedtemperatures.Toovercometheselimitations,additionalelementsareaddedtothesteeltogivealloysteelswithspecificproperties.Themainalloyingelementsincludemanganese,nickel,chromium,molybdenum,tungsten,vanadium,cobaltandsilicon.HardeningofPlainCarbonSteelAssteelisheatedabovethelowedcriticaltemperatureof1330F(721C)，thecarbonthatwasinthefromoflayersofironcarbideinpearlitebeginstodissolveintheironandfromasolidsolutioncalledaustenite.Whenthissolutionofironandcarbonissuddenlycooledorquenched，anewmicrostructureisformed.Thisiscalledmartensite.Martensiteisveryhardandbrittle，havingamuchhighertensilestrengththanthesteelwithapearlitemicrostructure.Itisquiteunstable，however，andmustbetempered(drawn)torelieveinternalstressesinordertohavetheductilityandtoughnessneededtobeuseful.AISIC1095，commonlyknownaswater-hardeningtool(W1)steel，willbegintoshowhardnesswhenquenchedfromatemperaturejustover1330F(721C)butwillnothardenatallifquenchedfromatemperaturelowerthan1330F(721C).Thissteelwillbecomeashardasitcangetwhenheatedto1450(788C)andquenchedinwater.Thisquenchingtemperaturechangesasthecarboncontentchanges.Itshouldbe50F(28C)abovetheuppercriticaltemperatureforcarbonsteelscontaininglessthan0.83percentcarbon.Thereasoncarbonsteel，lessthaneutectoid，shouldbeheatedabovetheuppercriticaltemperatureisthattheferriteisnotalltransformedintoaustenitebelowthispoint，andwhenquenched，isretainedinthemartensiticstructure.Theretainedferritecausesbrittlenessevenaftertempering.LowcarbonsteelssuchasAISI1020willnot，forallpracticalpurposes，hardenwhentheyareheatedandquenched.Oil-andair-hardeningsteelshaveahigherhardenabilityanddonothavetobequenchedasrapidlyasplaincarbonsteels.Consequently，theyaredeeperhardeningthanwaterhardeningtypes，whichmustbecooledto200F(93C)4within1or2seconds.Plaincarbonsteelscontaining0.83percentcarboncangetashard(RC67)asanyplaincarbonsteelcontainingmorecarbon.TemperingofPlainCarbonSteelTempering，ordrawing，isaprocessofreheatingasteelpartthathasbeenpreviouslytotransformsomeofthehardmartensiteintosofterstructures.Thehigherthetemperingtemperatureused，themoremartensiteistransformed，andthesofterandtougher(lessbrittle)thepiecebecomes.Therefore，temperingtemperaturesarespecifiedaccordingtothestrengthandductilitydesired.Mechanicalpropertiescharts，whichmaybefoundinsteelmanufacturershandbooksandcatalogs，givethesedataforeachtypeofalloysteel.temperatureandholdingitthereforalengthoftime，thencoolingitinairorwater.ApartcanbetemperedinafurnaceorovenbybringingittotherequiredSometoolsteelsshouldbecooledrapidlyaftertemperingtoavoidtemperbrittleness.Temperingshouldbedoneassoonaspossibleafterhardening.Thepartshouldnotbeallowedtocoolcompletely，sinceuntempereditcontainsveryhighinternalstressesandtendstosplitorcrack.Temperingwillrelievetheinternalstresses.Ahardenedpartleftovernightwithouttemperingmaydevelopcracksbyitself.ClassificationofHeatTreatingProcessesInsomeinstances，heattreatmentproceduresareclearcutintermsoftechniqueandapplicationwhereasinotherinstances，descriptionsorsimpleexplanationsareinsufficientbecau