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FerrousCastingAlloysFerrousCastingAlloysIntroductionIron-CarbonPhaseDiagramBasicCastIronMetallurgyCastIronsMicrostructuralFormationSolidificationSpecifications,propertiesandapplicationsCastSteelsFerrousCastingAlloysLiterallyiron-basedcastingalloysCastIron–ironalloywithsignificantCandSiGrayDuctileCompactedGraphiteAustemperedDuctileMalleableSpecialtyCastSteel–ironalloywithlowCandSiFerrousCastingAlloysAnderson,p.269Iron–CarbonPhaseDiagramASMVol.3,p.2.110Iron–CarbonPhaseDiagramPointsofnotePhasechangesofpureiron()Eutectic,eutectoid&peritecticreactionsGraphiteisstable,butmetastableFe3C(akacementiteorironcarbide)occursfrequentlyDesiredforcastirons:graphiteeutecticproduct,cementiteeutectoidproductIron–CarbonPhaseDiagramWhatmicroconstituentsarepossibleoncoolingfromaustenite?DependsoncoolingratePearliteBainite–upperandlowerMartensiteIron–CarbonPhaseDiagramASMVol.3,p.2.110PearliteLowestrelativecoolingratesAteutectoidcomposition(0.78%C)Theeutectoidproduct–ferrite+cementite–growinlamellarformNucleatesatprioraustenitegrainboundariesPearliteSamuels,p.317PearliteSlowestrelativecoolingratesAteutectoidcomposition(0.78%C)Theeutectoidproduct–ferrite+cementite–growinlamellarformNucleatesatprioraustenitegrainboundariesCoolingratedeterminesinterlamellarspacingLowerrates–coarsespacingMoremassivecementiteplateletsmeanlowerstrength&bettermachinability20–23HRCHigherrates–finespacingHigherstrength&poorermachinability30–35HRCPearliteRC&W,p.361PearliteOffeutectoidcompositionHypoeutectoidFerritenucleatesatgrainboundariesPearlitegrowsateutectoidtemperatureHypereutectoidCementitenucleatesatgrainboundariesPearlitegrowsateutectoidtemperatureCastironsare(extremely)hypereutectoidWe’lldiscussthisfurtherwithsteelsBainite&MartensiteBainiteIntermediatecoolingratesFerrite“l(fā)ath”withFe3CTwotypesUpperbainite-“l(fā)owerintermediate”coolingrateLowerbainite-“higherintermediate”coolingrateMartensiteHighestcoolingrates(quenchingrequired)Carbon-austenitesolidsolutionUniquecrystalstructure–BCTTheseareunimportantincastironmetallurgyIronCastingsBriefHistory~3000BC–Firstcastobjects(copper)600BC-Firstcastironobject(a600lb.tripod)castinChina1500AD–Sandfirstusedamoldingmedia1646–FirstAmericanironfoundry–nearBoston1722–Malleableironisdeveloped1750–ParliamentprohibitsironcastinginAmericancolonies1794–Cupolameltingdeveloped1863–Metallographydeveloped,metallographsbecomeavailablein19111899–Firstelectricarcfurnacebeginsproduction1900–BrinellhardnesstestintroducedIronCastingsBriefHistory1906–Firstinductionfurnaceinstalled1918–Firstautomatedfoundry–grenadehulks1930–Firstcorelessinductionfurnaceinstalled1943–Ductileirondiscovered;patented&commercializedin1949(Fordswitches100%ofcrankshaftproductiontoductileironin1951)1957–Vertically-partedmoldingisinvented(DISA)1962–Firstautomatedgreensandmoldingmachine1976–Compactedgraphiteironisdeveloped1990–KeyCoreprocessemployedforprecisiongrayironcastingsSource:ModernCasting,November2002CastIronsCharacterizedbyfreegraphiteinmatrixofferriteandcementite(eutectoidpearlite)TypesaredifferentiatedbytheformofthefreegraphiteICH,p.145CastIronsCharacterizedbyfreegraphiteinmatrixofferriteandcementite(ferriteorpearlite)TypesaredifferentiatedbytheformofthefreegraphiteEssentiallyFe-C-Sialloy(ternary)BasicCastIronMetallurgyFe-Fe3C-Si@2%SiICH,p.135BasicCastIronMetallurgyEutecticcompositionvarieswithsilicon(andphosphorus)contentCarbonEquivalentCE=%C+(%Si+%P)/3CEateutectic=4.3Grayironishypoeutectic(CE=3.9–4.1)Ductileironishypereutectic(CE=4.3–4.6)BasicCastIronMetallurgyCbecomeslesssolubleinausteniteastemperaturedropsbeloweutectictemperatureCdiffusestographiteparticlesGrayIronFullypearliticmatrixaround(normal)coarseflakesFerritematrixaroundfinegraphiteflakesDuctileIronFerrite“bullseye”aroundnodulesRapidcoolingresultsinfullypearliticmatrixAteutectoidtemperature,remainingcarboninaustenitebecomespearliteBasicCastIronMetallurgyChill–castironcooledtoorapidlyformsaustenite-carbideeutectic(whiteiron)insteadofaustenite-graphiteeutecticCheckforchillbypouringachillwedgeMeasureofsectionthicknessthatcanbecastfreeofcarbideCompositioneffectsdepthofchillHigherCE=thinnersectionsBasicCastIronMetallurgyShrinkage–threecomponentsLiquid–contractiononcoolingSolidification–volumetricchangeonchangingfromliquidtosolidSolid–contractiononcoolingControlliquidandsolidificationshrinkagebymaintainingsupplyofhotmetal-risersControlsolidshrinkagebybuildingpatternsslightlyoversizedGrayIronGrayIronGraphiteinflakeform(ASTMA247TypeVII)inamatrixofpearliteFerritenearfinegraphiteflakesGraphiteandaustenitegrowsimultaneouslybyeutecticreactionwhencoolingrateisslow(littleundercooling)EvenextremelyhypoeutecticironsAthighercoolingrates(moreundercooling),somedendritegrowthoccursRapidlycooledironwillformFe3CinsteadofgraphiteGrayIronGrayIronFlakeformischaracterizedinASTMA247TypeA(Random)–mostpreferredorientationbecauseisotropicpropertiesTypeB(Rosette)–acceptableProducedbymorerapidsolidification–oftenonsurfacesFerritemaybeassociatedwithTypeBTypesD&E(Interdendritic)–unacceptablebecauseofresultinganisotropyProducedbyrapidsolidificationorinsufficientinoculation(significantundercoolingoccurs)TypeC(Kish)–unacceptableduetodegradationofpropertiesResultofprimarygraphiteprecipitationinhypereutecticironsGrayIronICH,p.146GrayIronFlakesizeisalsocharacterizedinASTMA247ExtremelylargeflakesundesirableShrinkageGraphiteismuchlowerdensitythaniron,sovolumetricexpansionduringformationhelpstooffsetcontractionofironFeedseasily–noorsmallrisersGrayIronCompositionStrengthofgrayironincreaseswithdecreasingCE(volumefractionofgraphite)Alloyingelements(Cu,Cr,etc.)increasestrengthbysolidsolutionstrengtheningofferriteBookhastypicalcompositionsGrayIronPropertiesWeaknessesNotparticularlystrongorductileNotnotchsensitive–flakesactas“preexistingnotches”PoorimpactstrengthLowelasticmodulus(about10Msi)StrengthsGoodcompressivestrengthGoodthermalconductivityVerygooddampingcapacityExcellentslidingwearresistance–graphitelubricationExcellentmachinability–graphite“notches”ExcellentcastabilityGrayIronSpecifications–SAEJ431(Dec2000)SAECastingGradesFormerSAEGradesUltimateTensileStrength(MPa)G9H12G1800124G9H17G2500170G10H18G3000198G11H18G3000217G11H20G3500239G12H21G4000272G13H19G4000268GrayIronApplicationsCylinderblocks(WSD-M1A288-A4)Cylinderheads(WSD-M1A288-A4)BalanceShaftsDuctileIronDuctileIronGraphiteinnodularform(ASTMA247TypeI)inamatrixofferrite,pearliteoracombinationakaNodularIronMatrixdependsoncoolingrate,compositionNoduleformationIronmeltislowinsulfurandtreatedwithcertainelements(Mg,Ce,RE)toencouragegraphitetoformnodulesEffectoftreatmentfadeswithtimeUntreatedorfadedironwillformasgrayironHypereutectic,sographitebeginstoforminliquidaboveeutectictemperatureGraphitefloatationisobservedinslowlycooledheavysectionsDuctileIronDuctileIronNoduleshapeisimportantGivesductileironhigherstrength/ductilityCharacterizedby“%Nodularity”–percentageofgraphitehavingASTMA247TypeIformGoodductileironhasinexcessof80%nodularityPropertiesdon’tdegradesignificantlyuntilflake(TypeVII)appearsNodulecountisofsecondaryimportanceVariesdirectlywithcoolingrateInoculationjustpriortopouringincreasesnodulecountHighernodulecountgivesmarginallybetterductilityDuctileIronShrinkageAgainduetoexpansionupongraphiteformation,shrinkageisminimalCompositionEutectictohypereutecticCESulfurmustbelow(<0.015%S)Smallamountoftreatmentelement(s)promotesnodularization(0.030%Mg)Alloyingelements(Cu,Mo,Ni)helptostabilizepearliteDuctileIronPropertiesGoodcastabilityGoodcombinationofpropertiesWidevarietyofproperties,dependingonmatrixmicrostructureAs-castorheattreatedDuctileIronSpecifications–SAEJ434GradesMatrixStructureHardness(HB)UTS(MPa)YS(MPa)Elongation%D4018Ferrite170Max41427618D4512F–P156/21744831012D5506P–F187/2555523796D7003Pearlite241/3026894833DQ&TMartensiteVariousDuctileIronApplicationsCrankshafts(WSE-M1A172-B1/B2/B3)FEADBrackets(SAEJ434D4512)ChassisComponents(SAEJ434D4512/D5506)SpecialtyCastIronsSpecialtyCastIronsCompactedGraphiteIronAustemperedDuctileIronMalleableIronWhiteIronHighSilicon-MolybdenumDuctileIronCompactedGraphiteIronGraphiteinvermicularform(ASTMA247TypeIV)inamatrixofferrite,pearliteoracombinationGraphiteformationIntentionalundertreatmentofductileiron“Spoiling”ductileironwithelementsthatdegradenodules(lead,titanium,etc.)ProductionistrickyforthesereasonsPropertiesIntermediatebetweengrayandductileironCompactedGraphiteIronSpecifications–SAEJ1887ApplicationsCylinderblock–FOELion(V6)dieselAustemperedDuctileIronSameproductionmethodsandmicrostructureasconventionalductileironSpeciallyheattreated(austempered)toproducean“ausferrite”matrixTransformationtemperatureeffectspropertiesPropertiesMechanicalpropertiesandtoughnessgreatlyincreasedoverconventionalductileiron,excellentwearresistanceAustemperedDuctileIronSpecifications–SAEJ2477ApplicationsNonecurrentlyPossible–crankshafts,gears,bracketsMalleableIronGraphitein“tempergraphite”forminamatrixofferrite,pearlite,acombinationortemperedmartensiteGraphiteformationIroniscast(solidified)ascarbidic(white)iron,thenheattreatedtoconvertthecarbideintographitePropertiesSimilartoductileironApplicationsNone–heattreatmentmakesproductionexpensiveWhiteIronSolidificationratepreventsgraphiteprecipitation–Fe3CplateletsprecipitateinapearliticmatrixCanbeproducedinawholecastingorselectivelyWholecasting–composition(alloying)Selectively–chillsPropertiesExtremelyhighhardness(HB400–600)ApplicationsHighwearandabrasionapplicationsDAMBcamshaftlobesarechilledWhiteIronHiSi