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1、《机械工程专业英语》李光布饶锡新主编Lesson2CarbonandAlloySteelLesson2CarbonandAlloySteelTEXTSteelisprobablythemostwidelyusedmaterialformachineelementsbecauseofitspropertiesofhighstrength,highstiffness,durabilityandrelativeeaseoffabrication.Thetermsteelreferstoandalloyofiron,carbon,mang
2、aneseandoneormoreothersignificantelements.Carbonhasaverystrongeffectonthestrength,hardnessandductilityofanysteelalloy.Theotherelementsaffecthardenability,toughness,corrosionresistance,machinabilityandstrengthretentionathightemperatures.Theprimaryalloyingelementspresen
3、tinthevariousalloysteelsaresulfur,phosphorus,silicon,nickel,chromium,molybdenumandvanadium.1.ImportanceofCarbonAlthoughmoststeelalloyscontainlessthan1.0%carbon,itisincludedinthedesignationbecauseofitseffectonthepropertiesofsteel.AsFigure1.2illustrates,thelasttowdigits
4、indicatecarboncontentnhundredthsofapercent.Ascarboncontentincreases,strengthandhardnessalsoincreaseunderthesameconditionsofprocessingandheattreatment.Sinceductilitydecreaseswithincreasingcarboncontent,selectingsuitablesteelinvolvessomecompromisebetweenstrengthandducti
5、lity.Asaroughclassificationscheme,alow-carbonsteelisonehavingfewerthan30pointsofcarbon(0.30%).Thesesteelshaverelativelylowstrengthbutgoodformability.Inmachineelementapplicationswherehighstrengthisnotrequired,low-carbonsteelsarefrequentlyspecified.Ifwearisapotentialpro
6、blem,low-carbonsteelscanbecarburizedtoincreasethecarboncontentintheveryoutersurfaceofthepartandtoimprovethecombinationofproperties.Medium-carbonsteelscontain30to50pointsofcarbon(0.30%-0.50%).Mostmachineelementshavingmoderatetohighstrengthrequirementswithfairlygoodduct
7、ilityandmoderatehardnessrequirementscomefromthisgroup.High-carbonsteelshave50to95pointsofcarbon(0.50%-0.95%).ThehighcarboncontentprovidesbetterwearpropertiessuitableforapplicationsrequiringProvidedbyzcj085-7-《机械工程专业英语》李光布饶锡新主编Lesson2CarbonandAlloySteeldurablecuttinged
8、gesandforapplicationswheresurfacesaresubjectedtoconstantabrasion.Tools,knives,chisels,andmanyagriculturalimplementcomponents
