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首页 合金钢 不锈钢

合金钢 不锈钢.pdf

合金钢 不锈钢

waterrofg
2009-07-01 0人阅读 举报 0 0 暂无简介

简介:本文档为《合金钢 不锈钢pdf》,可适用于考试题库领域

TABLEOFCONTENTSIntroductionStainlessSteelsNickelBaseAlloysRoleofAlloyingElementsChromiumNickelMolybdenumMinorElementsDesignationsforCastStainlessSteelandNickelBaseAlloysCorrosionResistantCastingsStainlessSteelsMartensiticAusteniticDuplexNickelBaseAlloyCastingsHeatResistantCastingsStainlessSteelsNickelBaseAlloysCrNiAlloyandHighPerformanceNickelBaseAlloyCastingsforHeatResistingandElevatedTemperatureCorrosionApplicationsFabricationCastingMethodsMachiningWeldingPurchasingConsiderationsWorksCitedTrademarksSuggestedAdditionalReadingAppendixAAppendixBAppendixCINTRODUCTIONThisbrochurewillassistendusers,specifiers,anddesignersintheselectionofcorrosionandheatresistantnickelbaseallycastingsInformationonthealloys,castingmethods,propertiesandfabricationanddesignconsiderationsareprovidedtoaidinevaluationandselectionTypicalapplicationshavebeenprovidedforreferencepurposesbut,becauseserviceconditionsandperformancerequirementsvary,theuserisencouragedtoobtainmoreinformationfromthesupplierbeforemakingafinaldecisionCastings•STAINLESSSTEELSStainlesssteelsaredistinguishedfromothersteelsbyaminimumchromiumcontentof,whichmakesthemmoreresistanttocorrosiveaqueousenvironmentsandtooxidationAlthoughthereareexceptions,stainlesssteelcastingsareclassifiedas"corrosionresistant"whenusedinaqueousenvironmentsandvaporsbelow°F(°C)and"heatresistant"whenusedabovethistemperatureTheusualdistinctionbetweentheheatandcorrosionresistantcastinggradesiscarboncontentForastainlesssteelcastingtoperformwellinacorrosiveenvironment,thecarboncontentmustbelowHeatresistantgradeshavehighercarboncontentstoimproveelevatedtemperaturestrengthThechemicalcompositionandmicrostructuredifferencesbetweenthewroughtandcastversionsofstainlesssteelscanaffectperformance(SeeRoleofAlloyingElements)Somestainlesssteelcastinggradescanbeprecipitationhardenedbyheattreatment,butthemechanicalpropertiesofmostrelyontheirchemicalcompositionTheyieldandtensilestrengthsofcastingsarecomparabletotheirwroughtequivalentsCaststainlesssteelsgenerallyhaveequivalentcorrosionresistancetotheirwroughtequivalents,buttheycanbecomelesscorrosionresistantduetolocalizedcontamination,microsegregation,orlackofhomogeneityForexample,moldqualitymaycausesuperficialcompositionalchangesthatinfluenceperformance,andcarbonpickupfrommoldreleaseagentscanaffectcorrosionresistanceHeattreatmentandweldrepairprocedurescaninfluencetheperformanceofsomecastgradesandshouldbetakenintoconsiderationduringgradeselectionAdditionalinformationaboutthecharacteristics,propertiesandapplicationsofspecificcaststainlesssteelgradescanbefoundinthefollowingcorrosionandheatresistantsectionsNICKELBASEALLOYSExceptforsomeofthehighsiliconandproprietarygrades,castnickelbasealloysgenerallyhavewroughtapproximateequivalentsAlthoughthecastandwroughtversionsofnickelbasealloysarecommonlyusedincombinationbecausetheyprovidesimilarperformance,therearesomechemistrydifferences,primarilytoimprovecastabilityandsoundnessLikestainlesssteels,nickelbasecastingsarecategorizedascorrosionresistantiftheyareusedinaqueousenvironmentsandvaporsbelow°F(°C)andheatresistantiftheyarecapableofcontinuousorintermittentuseforsustainedtimesabovethistemperatureCarboncontentisusuallyadistinguishingfactorbetweentheheatandcorrosionresistantalloys,butthisdividinglinecanbevague,particularlyforalloysusedinthe°F(to°C)rangeAdditionalinformationaboutthecharacteristics,propertiesandapplicationsofspecificcastnickelbasealloyscanbefoundinthefollowingcorrosionandheatresistant•CastingsROLEOFALLOYINGELEMENTSChromium,nickel,andmolybdenumaretheprimaryalloyingelementsthatdeterminethestructure,mechanicalproperties,andcorrosionresistanceofstainlesssteelandnickelbasealloycastingsNickelandchromiumhavethegreatestinfluenceonheatresistantcastingsIntentionaladditionsoflessthancarbon,nitrogen,niobium,tantalum,titanium,sulfur,andslightlylargeradditionsofcopper,manganese,silicon,andaluminumareusedtomodifypropertiesSomeminorelementscanhaveapositiveornegativeeffectonpropertiesdependingontheapplicationCHROMIUMAstainlesssteelcontainsaminimumofchromiumbecausethislevelofchromiumcausesthespontaneousformationofastable,transparent,passive,protectivefilmIncreasingthelevelofchromiumenhancescorrosionresistanceAtelevatedtemperatures,chromiumprovidesresistancetooxidationandsulfurcontainingandothercorrosiveatmospherescontributestohightemperaturecreepandrupturestrengthand,insomealloys,increasesresistancetocarburizationNICKELNickelinstainlesssteelspromotesthestabilityofausteniteAusteniteisstrongerandmorestableathighertemperaturesthenferriteLessnickelisneededtoretainanausteniticstructureasthenitrogenorcarbonlevelsincreaseWhensufficientnickelisaddedtoachromiumstainlesssteel,thestructurechangesfromferritictoausteniticAddingnickelimprovestoughness,ductility,andweldabilityNickelincreasesresistancetooxidation,carburization,nitriding,thermalfatigue,andstrongacids,particularlyreducingacidsItisanimportantalloyingelementinstainlesssteelandnickelbasealloysusedforcorrosiveandhightemperatureapplicationsWollastonAlloys,Inc,Braintree,MassachusettsThis,pound(kg)mainfeedboosterpumpandapound(kg)adaptorareusedonaircraftCastings•AtlasFoundryMachineCompany,Tacoma,WashingtonStainlesssteelpumpcasingsareproducedinavarietyofsizesandshapesforpipeline,refining,andboilerfeedapplicationsMOLYBDENUMMolybdenumadditionsimproveresistancetopittingandcrevicecorrosioninchloridecontainingenvironmentsandcorrosionbysulfuric,phosphoric,andhydrochloricacidsTheelevatedtemperaturemechanicalpropertiesofausteniticstainlesssteelsandthestrengthandtemperingresistanceofmartensiticstainlesssteelsareimprovedbymolybdenumMINORELEMENTSThepresenceofsmallamountsofcarbonandnitrogencannotbeavoidedduringmeltingInsomegrades,theseelementsareaddeddeliberatelyIncreasingthecarboncontentinhightemperaturealloysimproveshightemperaturestrengthandcreepresistance,butreducesductilityConversely,carboncanbedetrimentaltocorrosionresistancewhenitcombineswithchromiumtoformchromiumcarbidesalonggrainboundariesThisreducesthechromiumadjacenttothegrainboundary(sensitization)andcanleadtocorrosionofchromiumdepletedareas(intergranularcorrosion)Titanium,columbium,andtantalumadditionspreferentiallycombinewithcarbonandnitrogentopreventsensitizationandeliminatesusceptibilitytointergranularcorrosionNitrogenadditionstoausteniticandduplexstainlesssteelsimprovepittingresistanceandretardthekineticsofsigmaphaseformationAdditionsofsulfur,selenium,andleadinstainlesssteelimprovemachinabilityColumbiumadditionscanimprovehightemperaturecreepstrengthCopperadditionsimproveresistancetosulfuricacidAcombinationofmanganeseandnitrogenmaybeusedasapartialsubstitutefornickelinsomestainlesssteelsSiliconisaddedtocaststainlesssteelgradestoincreasecastingfluidityandimprovecastabilityAscarbonplussiliconcontentisincreased,partialeutecticsolidificationimprovescastabilityandcastingsoundnessSiliconisgenerallylimitedtoincastingsintendedforserviceabove°F(°C)becauseitlowersthehightemperaturecreepandrupturepropertiesSiliconalsoimprovesoxidationresistance,particularlywhereelementswithavolatileoxidesuchastungstenorniobium(columbium)areusedtoimprovehightemperaturestrengthIncarburizingatmospheressuchasethylenefurnaces,siliconlevelsashighashavebeenfoundtobebeneficialAluminumalsoimprovesresistancetooxidation•CastingsDESIGNATIONSFORCASTSTAINLESSSTEELANDNICKELBASEALLOYSInNorthAmerica,thecommondesignationsforcaststainlesssteelandnickelbasealloysaredescriptiveoftheirchemistryandpurposeThisdesignationsystemwasestablishedbytheAlloyCastingInstitute(ACI)andhasbeenadoptedbyASTMAdesignationbeginningwiththeletter"C"indicatesthatthealloyisusedprimarilyforcorrosiveserviceifthefirstletteris"H",thealloyisusedprimarilyforhightemperatureserviceatorabove°F(°C)ThesecondletterindicatestheapproximatenickelandchromiumcontentsofthealloygradeontheFeCrNiternarydiagram(ASTMA,AppendixXandFigureX)ForCclassifications,thesingleordoubledigitnumberfollowingthefirsttwolettersindicatesthemaximumcarboncontentofthegrade(x)ForHclassifications,thisnumberisthemidpointofthecarboncontentrangeinunitsofwitha±limitOtheralloyingelements,ifpresent,arerepresentedbyoneormorelettersfollowingthenumberForexample,thedesignationCFMindicatesthatthegradeiscorrosionresistant(C),containsbetweenandchromiumandbetweenandnickel(F),amaximumcarboncontentof(),andmolybdenum(M)HDindicatesthatthegradeisheatresistant(H),andcontainsbetweenandchromiumandbetweenandnickel(D)ThisCANM,inch(mm)multibowlwellheadChristmastreeassemblyisusedinNorthSeasourgasproductionRayAtkinsonCORROSIONRESISTANTCASTINGSSTAINLESSSTEELSThecorrosionresistant,cast,stainlesssteelgradesaregroupedintofamiliesbasedontheirmicrostructure(martensitic,austenitic,orduplex)GeneralcharacteristicsofeachstainlesssteelfamilyandspecificinformationabouteachofthewidelyusedgradesareprovidedinthefollowingsectionsStainlesssteelcastingsareclassifiedas"corrosionresistant"iftheyareusedinaqueousenvironmentsandvaporsbelow°F(°C)Forastainlesssteelcastingtoperformwellinacorrosiveenvironment,thecarboncontentandquantityofprecipitatedcarbidesinthemicrostructuremustbelowThecarboncontentincorrosionresistantgradesisusuallybelowandsometimesbelowIncreasingthechromiumcontentenhancescorrosionresistanceandnickelincreasesresistancetostrongacids,particularlyreducingacidsTheinfluenceofotheralloyingelementsisdiscussedintheRoleofAlloyingElementssectionThechemicalcompositions,ASTIVIspecifications,approximatewroughtequivalents,andcommonendusemicrostructuresofcorrosionresistantstainlesssteelcastingscanbefoundinTablesandTheASTIVIstrengthandelongationrequirementsareshowninTableandarecomparedinFiguresthroughTypicalshorttermhightemperaturepropertiesforseveralgradesareshowninTableStandardheattreatmentsareshowninTableTypicalhardness,impact,andphysicalpropertiesareshowninTablesthroughThesearecentrifugallycastCAturbinecombustorcasesWisconsinCentrifugal,Waukesha,Wisconsin,USA•CastingsCastings••CastingsCastings••CastingsCastings••CastingsFigureRelativetensilestrengthofcorrosionresistantstainlesssteelcastingsFigureRelativeyieldstrengthofcorrosionresitantstainlesssteelcastingsMARTENSITICThemostwidelyusedmartensiticgradesareCANM,CBCu,andCBCuMartensiticsareresistanttomoderateatmosphericcorrosionandmildorganicmediacorrosionTheircorrosionresistanceislowerthanthatofmorehighlyalloyedgrades,limitingtheiruseinprocessenvironmentsTheirstrengthandtemperingresistanceareimprovedbymolybdenumThesegradesareferromagnetic,hardenablebyheattreatment,andhavepoorlowtemperatureimpactstrengthTheycombinehardnesswithimprovedcorrosionresistanceovernonstainlesssteelsandareusedforcutlery,turbineblades,andhightemperaturepartsSectionthicknessesofaboutinch(mm)andabovecanbecastsatisfactorilySomewhatlightersectionsarefeasibledependingonthecastingdesignandpatternComplexdesignswithlightandheavysectionsarefeasible,butdrasticchangesinsectionthicknessshouldbeavoidedCastings•FigureRelativeelongationofcorrosionresistantstainlesssteelcastingsCAM(CrNi)UNSJCANcontainstheminimumchromiumlevelneededtoformapassivefilmItcombinesstrengthandtoughnesswithfairlygoodmachinabilityandweldabilityCANisresistanttoatmosphericcorrosionandstainingbymanyorganicmediainrelativelymildserviceCANM(MrNi)UNSJCANMisCANmodifiedwithmolybdenumtoimprovecorrosionresistanceandcastabilityItswroughtequivalentisFNM(S)CANMprovidesresistancetomildlycorrosiveenvironmentsunderoxidizingconditionsandgoodcavitationresistanceItisusedforlowtemperaturevalves,flanges,fittings,andotherpressurecontainingpartsto°F(°C)boilerfeedwaterto°F(°C)flowingseawatersulfurandwaterto°F(°C)Ithasbeenusedbythechemical,marine,oilandgas,pollutioncontrolandpowerindustriesforcasings,compressorimpellers,diaphragms,diffusers,dischargespacers,hydraulicturbineparts,impulsewheels,packinghousings,propellers,pumpimpellers,suctionspacers,andvalvebodiesandpartsCANMshouldbeheattreatedpriortouseandtemperedaftermajorweldrepairsDoubletemperingtoachievehardnessvaluesbelowHRCforwetHSenvironmentstypicallyconsistsofaustenitizingat°F(°C)followedbytemperingat°F(°C),andthenasecondtemperinqtreatmentat°F(°C)CA(Cr)UNSJCA(Cr)UNSJCAisanironchromiumalloycontainingtheminimumamountofchromiumnecessaryforclassificationasastainlesssteelItisresistanttoatmosphericcorrosionandstainingbymanyorganicmediainrelativelymildserviceandprovidesfairlygoodmachiningandweldingpropertiesCAisahighercarbonversionofCAThehighercarboncontentpermitsthegradetobehardenedtoamaximumofBHNandincreasesitsstrength•CastingsCBCu(CrNCu)UNSJCBCu(CrNiCu)UNSJCBCuandCBCuarehighstrength,lowcarbon,precipitationhardenablegradesthatarenotintendedforuseinthesolutionannealedconditionThewroughtequivalentsare(S)and(S)Thesegradesareusedinapplicationswherebothelevatedtemperaturestrength(upto°For°C)andcorrosionresistancearerequiredBotharesimilartoTypeinperformanceinmanyenvironmentsCBCuandCBCuhavegoodresistancetoatmosphericcorrosionandmanycorrosiveliquidsincludingethyleneglycolwater(to°Forto°C),foodproducts,pulpliquor,andwaterupto°F(°C)Commonapplicationsincludeairframecomponents,centrifugebowls,compressorimpellers,foodmachineryparts,machinetoolparts,propellershafts,pumpimpellers,rotors,screwflights,andvalvebodiesintheaerospace,aircraft,chemical,foodprocessing,gasturbine,marine,petrochemical,andpulpandpaperindustriesMachiningisdoneinthesolutionannealedconditionbeforeprecipitationhardeningtothedesiredstrengthlevelIfhomogenizingisdesiredpriortosolutionannealing,heatthecastingsto°F(°C)minimum,holdforhoursminimum,andthenaircooltobelow°F(°C)Becauseprecipitationhardeningisdoneatarelativelylowtemperature,thereislittledangerofcracking,distortion,oroxidationofthemachinedsurfacesSomeshrinkage(to)occursduringprecipitationhardeningThestandardprecipitationhardeningtreatmentsandtheresultantmechanicalpropertiesareshowninTableCastings•FigureEffectofelevatedtemperatureonstaticandcentrifugallycastCFwithaferritenumberoftoandNRefAUSTENITICWhilewroughtausteniticgradeshaveasinglephasemicrostructure,theircastequivalentsusuallyhaveasma

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