外文文献翻译摘自/制造工程与技术（机加工）（英文版）ManufacturingEngineeringandTechnologyMachining机械工业出版社2004年3月第1版页564560P美s/卡尔帕基安(Seropekalpakjian)s/r施密德(StevenR/Schmid)著原文：20/9MACHINABILITYThemachinabilityofamaterialusuallydefinedintermsoffourfactors/1、Surfacefinishandintegrityofthemachinedpart；2、Toollifeobtained；3、Forceandpowerrequirements；4、Chipcontrol/Thus/goodmachinabilitygoodsurfacefinishandintegrity/longtoollife/andlowforceAndpowerrequirements/Asforchipcontrol/longandthin(stringy)curedchips/ifnotbrokenup/canseverelyinterferewiththecuttingoperationbybecomingentangledinthecuttingzone/Becauseofthecomplexnatureofcuttingoperations/itisdifficulttoestablishrelationshipsthatquantitativelydefinethemachinabilityofamaterial/Inmanufacturingplants/toollifeandsurfaceroughnessaregenerallyconsideredtobethemostimportantfactorsinmachinability/Althoughnotusedmuchanymore/approximatemachinabilityratingsareavailableintheexamplebelow/20/9/1MachinabilityOfSteelsBecausesteelsareamongthemostimportantengineeringmaterials(asnotedinChapter5)/theirmachinabilityhasbeenstudiedextensively/Themachinabilityofsteelshasbeenmainlyimprovedbyaddingleadandsulfurtoobtainso-calledfree-machiningsteels/ResulfurizedandRephosphorizedsteels/Sulfurinsteelsformsmanganesesulfideinclusions(second-phaseparticles)/whichactasstressraisersintheprimaryshearzone/Asaresult/thechipsproducedbreakupeasilyandaresmall；thisimprovesmachinability/Thesize/shape/distribution/andconcentrationoftheseinclusionssignificantlyinfluencemachinability/Elementssuchastelluriumandselenium/whicharebothchemicallysimilartosulfur/actasinclusionmodifiersinresulfurizedsteels/Phosphorusinsteelshastwomajoreffects/Itstrengthenstheferrite/causingincreasedhardness/Hardersteelsresultinbetterchipformationandsurfacefinish/Notethatsoftsteelscanbedifficulttomachine/withbuilt-upedgeformationandpoorsurfacefinish/Thesecondeffectisthatincreasedhardnesscausestheformationofshortchipsinsteadofcontinuousstringyones/therebyimprovingmachinability/LeadedSteels/Ahighpercentageofleadinsteelssolidifiesatthetipofmanganesesulfideinclusions/Innon-resulfurizedgradesofsteel/leadtakestheformofdispersedfineparticles/Leadisinsolubleiniron/copper/andaluminumandtheiralloys/Becauseofitslowshearstrength/therefore/leadactsasasolidlubricant(Section32/11)andissmearedoverthetool-chipinterfaceduringcutting/Thisbehaviorhasbeenverifiedbythepresenceofhighconcentrationsofleadonthetool-sidefaceofchipswhenmachiningleadedsteels/Whenthetemperatureissufficientlyhigh-forinstance/athighcuttingspeedsandfeeds(Section20/6)theleadmeltsdirectlyinfrontofthetool/actingasaliquidlubricant/Inadditiontothiseffect/leadlowerstheshearstressintheprimaryshearzone/reducingcuttingforcesandpowerconsumption/Leadcanbeusedineverygradeofsteel/suchas10xx/11xx/12xx/41xx/etc/LeadedsteelsareidentifiedbytheletterLbetweenthesecondandthirdnumerals(forexample/10L45)/(Notethatinstainlesssteels/similaruseoftheletterLmeans“lowcarbon/”aconditionthatimprovestheircorrosionresistance/)However/becauseleadisawell-knowntoxinandapollutant/thereareseriousenvironmentalconcernsaboutitsuseinsteels(estimatedat4500tonsofleadconsumptioneveryyearintheproductionofsteels)/Consequently/thereisacontinuingtrendtowardeliminatingtheuseofleadinsteels(lead-freesteels)/Bismuthandtinarenowbeinginvestigatedaspossiblesubstitutesforleadinsteels/Calcium-DeoxidizedSteels/Animportantdevelopmentiscalcium-deoxidizedsteels/inwhichoxideflakesofcalciumsilicates(CaSo)areformed/Theseflakes/inturn/reducethestrengthofthesecondaryshearzone/decreasingtool-chipinterfaceandwear/Temperatureiscorrespondinglyreduced/Consequently/thesesteelsproducelesscraterwear/especiallyathighcuttingspeeds/StainlessSteels/Austenitic(300series)steelsaregenerallydifficulttomachine/Chattercanbesproblem/necessitatingmachinetoolswithhighstiffness/However/ferriticstainlesssteels(also300series)havegoodmachinability/Martensitic(400series)steelsareabrasive/tendtoformabuilt-upedge/andrequiretoolmaterialswithhighhothardnessandcrater-wearresistance/Precipitation-hardeningstainlesssteelsarestrongandabrasive/requiringhardandabrasion-resistanttoolmaterials/TheEffectsofOtherElementsinSteelsonMachinability/Thepresenceofaluminumandsiliconinsteelsisalwaysharmfulbecausetheseelementscombinewithoxygentoformaluminumoxideandsilicates/whicharehardandabrasive/Thesecompoundsincreasetoolwearandreducemachinability/Itisessentialtoproduceandusecleansteels/Carbonandmanganesehavevariouseffectsonthemachinabilityofsteels/dependingontheircomposition/Plainlow-carbonsteels(lessthan0/15%C)canproducepoorsurfacefinishbyformingabuilt-upedge/Caststeelsaremoreabrasive/althoughtheirmachinabilityissimilartothatofwroughtsteels/Toolanddiesteelsareverydifficulttomachineandusuallyrequireannealingpriortomachining/Machinabilityofmoststeelsisimprovedbycoldworking/whichhardensthematerialandreducesthetendencyforbuilt-upedgeformation/Otheralloyingelements/suchasnickel/chromium/molybdenum/andvanadium/whichimprovethepropertiesofsteels/generallyreducemachinability/Theeffectofboronisnegligible/Gaseouselementssuchashydrogenandnitrogencanhaveparticularlydetrimentaleffectsonthepropertiesofsteel/Oxygenhasbeenshowntohaveastrongeffectontheaspectratioofthemanganesesulfideinclusions；thehighertheoxygencontent/thelowertheaspectratioandthehigherthemachinability/Inselectingvariouselementstoimprovemachinability/weshouldconsiderthepossibledetrimentaleffectsoftheseelementsonthepropertiesandstrengthofthemachinedpartinservice/Atelevatedtemperatures/forexample/leadcausesembrittlementofsteels(liquid-metalembrittlement/hotshortness；seeSection1/4/3)/althoughatroomtemperatureithasnoeffectonmechanicalproperties/Sulfurcanseverelyreducethehotworkabilityofsteels/becauseoftheformationofironsulfide/unlesssufficientmanganeseispresenttopreventsuchformation/Atroomtemperature/themechanicalpropertiesofresulfurizedsteelsdependontheorientationofthedeformedmanganesesulfideinclusions(anisotropy)/Rephosphorizedsteelsaresignificantlylessductile/andareproducedsolelytoimprovemachinability/20/9/2MachinabilityofVariousOtherMetalsAluminumisgenerallyveryeasytomachine/althoughthesoftergradestendtoformabuilt-upedge/resultinginpoorsurfacefinish/Highcuttingspeeds/highrakeangles/andhighreliefanglesarerecommended/Wroughtaluminumalloyswithhighsiliconcontentandcastaluminumalloysmaybeabrasive；theyrequirehardertoolmaterials/Dimensionaltolerancecontrolmaybeaprobleminmachiningaluminum/sinceithasahighthermalcoefficientofexpansionandarelativelylowelasticmodulus/Berylliumissimilartocastirons/Becauseitismoreabrasiveandtoxic/though/itrequiresmachininginacontrolledenvironment/Castgrayironsaregenerallymachinablebutare/Freecarbidesincastingsreducetheirmachinabilityandcausetoolchippingorfracture/necessitatingtoolswithhightoughness/Nodularandmalleableironsaremachinablewithhardtoolmaterials/Cobalt-basedalloysareabrasiveandhighlywork-hardening/Theyrequiresharp/abrasion-resistanttoolmaterialsandlowfeedsandspeeds/Wroughtcoppercanbedifficulttomachinebecauseofbuilt-upedgeformation/althoughcastcopperalloysareeasytomachine/Brassesareeasytomachine/especiallywiththeadditionpflead(leadedfree-machiningbrass)/Bronzesaremoredifficulttomachinethanbrass/Magnesiumisveryeasytomachine/withgoodsurfacefinishandprolongedtoollife/Howevercareshouldbeexercisedbecauseofitshighrateofoxidationandthedangeroffire(theelementispyrophoric)/Molybdenumisductileandwork-hardening/soitcanproducepoorsurfacefinish/Sharptoolsarenecessary/Nickel-basedalloysarework-hardening/abrasive/andstrongathightemperatures/Theirmachinabilityissimilartothatofstainlesssteels/Tantalumisverywork-hardening/ductile/andsoft/Itproducesapoorsurface
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