不锈钢相图.docx

不锈钢相图.docx

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不锈钢相图

AEB-Lisaconventionallyingot-castmartensiticstainlesssteeldesignedandmanufacturedbyUddeholmToolingAB（Sweden）.Itsnominalchemicalcomposition（inweightpercent）isasfollows:

C=0.65

Cr=12.8

Si=0.4

Mn=0.65

Figure1showsthephasediagramofUddeholmAEB-Lstainlesssteel（indeg.Celsius）calculatedwithThermo-Calc,coupledwithTCFE3thermodynamicdatabase.

Figure1.PhasediagramofUddeholmAEB-Lstainlesssteel（indeg.Celsius）calculatedwithThermo-Calc,coupledwithTCFE3thermodynamicdatabase.Siliconandmanganesewereexcludedfromthermodynamiccalculations.

Theequilibriumvaluesforsolidusandliquidustemperatureswerecalculatedtobe1461°C（2661°F）and1379°C（2515°F）,respectively.

Inthetemperaturerangeof1144-1379°C（2091-2515°F）themicrostructureofUddeholmAEB-Lstainlesssteelconsistsofjustonesinglephase:

austenite.Thus,ifAEB-Lsteelishardenedfromanaustenitizationtemperaturethatishigherthan1144°C（2091°F）theresultingmartensiticmicrostructurewillcontainnoprimarycarbides.

Belowthetemperatureof1144°C（2091°F）thechromium-richM7C3primarycarbidesstarttoprecipitatefromtheausteniticmatrix.Attheaustenitizationtemperatureof,say,1052°C（1925°F）theequilibriumamountofchromium-richM7C3primarycarbidesis3.3molarpercent（2.6volumepercent）.Theequilibriumamountofcarbonandchromiumintheausteniticmatrixat1052°C（1925°F）is0.44wt.%and11.4wt.%,respectively.（Theamountofcarbonandchromiuminthematrixisagoodindicatorofthesteel'shardenabilityandcorrosionresistance,respectively.）

TheequilibriumvalueforA1temperature（eutectoidtemperature）wascalculatedtobe814°C（1497°F）.UnderequilibriumconditionstheausteniteinUddeholmAEB-Lstainlesssteeltransformsintoferriteatthistemperature.

Finally,pleaseseeadditionalinformationabouttheFe-Cr-Cternaryphasediagrams.

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•Phasediagram（indeg.Celsius）ofUddeholmAEB-Lstainlesssteel

•Phasediagram（indeg.Fahrenheit）ofUddeholmAEB-Lstainlesssteel

Martensiticstainlesssteelsuchas154CMcontainsabout4wt.percentmolybdenum（inadditionto1.05wt.%Cand14.0wt.%Cr）.Todeterminetheeffectof4wt.%MoontheFe-Cr-Cternarysystem,considerFigures5and6,whichshowtheisothermalsectionsofFe-4Mo-Cr-Cquaternaryphasediagramat1000°C（1832°F）and1100°C（2012°F）,respectively.

Figure5.IsothermalsectionofFe-4Mo-Cr-Cquaternaryphasediagramat1000°C（1832°F）calculatedwithThermo-CalccoupledwithTCFE2000thermodynamicdatabase.

AccordingtoThermo-Calccalculations,theausteniticmatrixofFe-4Mo-14Cr-1.05Calloyat1000°C（1832°F）hasthefollowingchemicalcomposition（inweightpercent）:

Cr=8.6

C=0.33

Mo=2.6

Theamountofchromium-richM23C6primarycarbidesinFe-4Mo-14Cr-1.05Calloyat1000°C（1832°F）iscalculatedtobe16.8mol.percent.Itisworthnotingthattheadditionof4wt.%MototheFe-Cr-CsystemexpandssignificantlythepresenceofM23C6phaseattheexpenseoftheM7C3phase（compareFigure1—IsothermalSectionofFe-Cr-CTernaryPhaseDiagramat1000°C—andFigure3—IsothermalSectionofFe-0.8Mo-Cr-CQuaternaryPhaseDiagramat1000°C—withFigure5）.

Figure6.IsothermalsectionofFe-4Mo-Cr-Cquaternaryphasediagramat1100°C（2012°F）calculatedwithThermo-CalccoupledwithTCFE2000thermodynamicdatabase.

AccordingtoThermo-Calccalculations,theausteniticmatrixofFe-4Mo-14Cr-1.05Calloyat1100°C（2012°F）hasthefollowingchemicalcomposition（inweightpercent）:

Cr=10.6

C=0.58

Mo=3.4

Theamountofchromium-richM23C6primarycarbidesinFe-4Mo-14Cr-1.05Calloyat1100°C（2012°F）iscalculatedtobe11.6mol.percent.

Theamountofchromiumandmolybdenuminthematrixisalsoanindicatorofthesecondary-hardeningresponse—ingeneral,thehighertheamountofchromiumandmolybdenuminthematrix,thestrongerthesecondary-hardeningresponseduringtempering（especiallyathighertemperingtemperatures.）

Part1:

Fe-Cr-CTernaryPhaseDiagrams

Part2:

Fe-0.8Mo-Cr-CQuaternaryPhaseDiagrams

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Ahighhardnesslevel,afinearrayofuniformlydistributedprimaryalloycarbides,andanadequatematrixchromiumcontentarethethreemostdesiredpropertiesrequiredtoproduceaknifewithoptimumproperties.Ideally,amartensiticstainlesssteelgradeforknifeapplicationsshould,therefore,satisfythefollowingtwofundamentalrequirements:

（1）Thecarboncontentoftheausteniticmatrixhastobearound0.6wt.pct.orhigherinordertoachievethehardnessof63-64HRC.

（2）Thechromiumcontentoftheausteniticmatrixhastobeatleast12wt.pct.inordertoensurecorrosionresistance.（Itshouldbesaid,however,thatapartofmatrixchromiumcanbereplacedwithmolybdenumwithlittleornonegativeconsequencesforcorrosionresistance.）

IsothermalsectionsoftheFe-Cr-Cternaryphasediagramareagoodstartingpointwhenitcomestounderstandingthevarioustrade-offsbetweentheaustenitizationtemperatureselectedforheattreatmentandtheresultingchemicalcompositionoftheausteniticmatrix.

ThecompositionplanefortheFe-Cr-Cternaryphasediagramat1000°C（1832°F）isshownonFigure1.Thecarboncontentisplottedalongthehorizontalaxisandthechromiumcontentalongtheverticalaxisofthecompositionplane.

Figure1.IsothermalsectionofFe-Cr-Cternaryphasediagramat1000°C（1832°F）calculatedwithThermo-CalccoupledwithTCFE2000thermodynamicdatabase.

TheisothermalsectioninFigure1showsthecontentofchromiumandcarboninthevariousphasesofFe-Cr-Calloysthatcanexistat1000°C（1832°F）.Thearealabeledγ（theGreeklettergamma）representsaustenite.IfthecompositionofanFe-Cr-CalloyisplottedonFigure1anditfallsinsidetheγarea,themicrostructureofthatalloywillconsistofausteniteonly,i.e.,nocarbideswillbepresentat1000°C（1832°F）.

ConsidernowoneofthemostbasicmartensiticstainlesssteelgradessuchasAISI440C（approximately17wt.pct.chromiumand1.075wt.pct.carbon）,plottedonthecompositionplaneofFigure1.Itschemicalcompositionfallsinsideoftheregionlabeledγ+M7C3.ThismeansthatifAISI440Cisheatedto1000°C（1832°F）itsmicrostructurewillconsistofausteniteandchromium-richM7C3primarycarbides.Uponquenchingthemartensiteformedfromtheaustenitewillcontainchromium-richM7C3primarycarbidesdispersedwithinit.

ItisworthnotingthatonFigure1theright-handboundaryoftheausteniteregionislabeled"CarbonSaturationLine".Thislineisimportantasittellsusthemaximumamountofcarbonthataustenitecandissolvewithinitself—additionofmorecarbonwouldprecipitatecarbides.

Thefurtherthealloycompositionliestotherightofthesaturationline,thelargerthevolumefractionofchromium-richM7C3primarycarbidesitwillcontain.Thepresenceofchromium-richM7C3primarycarbidesrenderstheaustenitedepletedinbothchromiumandcarbonrelativetotheoverallchemicalcompositionofthealloy.

Figure1canbeusedtodeterminethechemicalcompositionoftheausteniteinanalloysuchasAISI440C.TheaustenitecompositionforAISI440Cat1000°C（1832°F）isfoundatthepointwherethetielinedrawnthroughAISI440Cintersectsthecarbonsaturationline.ItisworthnotingthateventhoughAISI440Calloycontains1.075percentofcarbonand17percentofchromiumoverall,theaustenitethatformsat1000°C（1832°F）containsonlyaround0.3percentofcarbonand11.7percentofchromium（seeFigure1）.Themartensitethatformsuponquenchinghasthesamechemicalcompositionastheaustenite.Thecarbonandchromiumcontentsofthemartensitehave,inturn,theeffectonitshardnessandcorrosionresistance,respectively.Thus,AISI440Cmartensiticstainlesssteel,whenhardenedfrom1000°C（1832°F）,doesnotsatisfythetworequirementsstatedabove（thecarbonandchromiumcontentofthematrixofatleast0.6and12percent,respectively）.

Todemonstratetheeffectofincreasingtheaustenitizationtemperatureonthevolumefractionofprimarycarbidesandthechemicalcompositionoftheaustenite,considerthechangeinthepositionofthecarbonsaturationlineinFigure2.

Figure2.IsothermalsectionofFe-Cr-Cternaryphasediagramat1100°C（2012°F）calculatedwithThermo-CalccoupledwithTCFE2000thermodynamicdatabase.

Whentheaustenitizationtemperatureisincreasedfrom1000°C（1832°F）to1100°C（2012°F）,thecontentofcarbonandchromiumintheausteniticmatrixisincreasedfrom0.3%C/11.7%Crto0.5%C/13.2%Cr.Thevolumefractionofchromium-richM7C3primarycarbidesissmallerat1100°C（2012°F）thanat1000°C（1832°F）,asgraphicallydemonstratedbythelengthofthetielineinFigures1and2.

TheSecondEditionofHeatTreater'sGuide—PracticeandProceduresforIronsandSteels（publishedbyASMInternationalin1995）recommendsthatAISI440Cbeaustenitizedat1010°C-1065°C（1850°F-1949°F）.Formaximumcorrosionresistanceandstrength,theGuiderecommendstheupperendoftheaustenitizationrange.Sucharecommendationisnotsurprising.Theabovegivenphasediagramsdemonstrateth