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1、MicrostructuralEvolutionofSlagsduringEAFStainlessSteelmakingDURINCKDirk1JONESPeterTom1GUOMuxing1VERHAEGHEFrederik1HEYLENGert2HENDRICKXRoel2BAETENRik2BLANPAINBart1WOLLANTSPatrick1(1.DepartmentofMetallurgyMaterialsEngineer

2、ingKatholiekeUniversiteitLeuvenKasteelparkArenberg44BE3001Heverlee(Leuven)Belgium2.UgineSlagmicrostructureIndustrialexperimentsSpinelparticlesSlagbasicityCrrecovery0IntroductionTheelectricarcfurnace(EAF)istheprimarystage

3、instainlesssteelmaking.Targetedslagissuesare:(1)earlyliquidslagfmation[1](2)slagfoaming[23](3)chromiumrecovery[45](4)immobilisationoftheremainingCrOxtoenhancetheslagvalisationpotential[6].Allthesephenomenaareaffectedsome

4、howbythehightemperatureslagmicrostructure[257].Althoughsomestudiesdealwiththeinfluenceofslagmicrostructure[1810]thepresenteddataarerelativelybasicinthatrespect.Thispapertherefepresentsanextendedmicrostructuralacterisatio

5、nofEAFstainlesssteelslagsbasedonanobservationalstudyof36austeniticheats.1ExperimentalmethodsThestudywasperfmedinU&ABelgium(Genk).ItsmeltshopconsistsoftwoEAFunits(‘EAF1’‘EAF2’120tonnes).EAF1isanexcentricbottomtypefurnacew

6、hereatthetimeoftheexperimentsnoslagfoamingpracticewasattempted.EAF2isaspouttypefurnacewithanexchangeablerefractyvesselaCO2lance.TheoperationalpracticefEAF2startswiththeloadingofsteelscrapFeCralloys.FeSilimedolomiticlimea

7、readdedinsuchamountsthatarelativelybasicslagobtained.WhenaliquidbathisreachedCO2areinjectedindertoaddchemicalenergytogenerateafoamyslag.Oxygenflowratesare20to30Nm3minfabout10minutes.Carbonisinjectedatarateof30kgmin.After

8、blowingFeSiisaddedtoreduceCrOxintheslag.Finallythemeltistappedintoatransferladle.Theslagsamplinginvolvesdippingasteelrodintheslagtakingaslagsamplebyalongspoonpouringitoutonaconcreteflo.Theassociatedcoolingratesenablethee

9、xtractionofthehightemperaturemicrostructure.EachEAF2heatwassampledbefeCO2injection(A)halfwayduringCO2injection(B)afterCO2injection(C)befetapping(D)aftertappinginthetransferladle(E).OnlythreesampleswerecollectedfEAF1heats

10、:befeFeSialloyaddition(C)justbefetapping(D)aftertappinginthetransferladle(E).Table1:ObservedrangeoftheglobalslagcompositionduringEAF2process(wt%basicityas(CM)S)(MnOTiO250m)hasacompositionsimilartothatofstainlesssteel.The

11、separticlesiginatefromthesteelbath.Theycanbesplashedintotheslagduringmeltingbyfallingscrap.HanHolappa[12]pointoutthatrisinggasbubblesdragsteelletsalongthebathintotheslag.Thismeansthatslagfoamingcanleadtoadditionalmetallo

12、sses.Secondlysmallermetalparticles(5m)areobservedinvastamountsinalmosteveryslagsample.Fabout25%oftheseletsthecompositioncrespondstothatofstainlesssteel.Thecompositionoftheother75%howeverdeviatesfromthatofstainlesssteel.T

13、helatterletspredominantlyconsistofFeCrwithlittlenoNi.AccdingtothereactionmodelofGustafssonVikman[10]theseletsarefmedbythereactionbetweenmetaloxidesintheslagCObubbles.AsFeOistheleaststableoxideintheslagphasethisoxideisini

14、tiallyreducedfmingsmallliquidironletswithintheslag.AsthelevelofFeOintheslagdecreasestheparallelreactionbetweenCrOxCOgasbecomesmeimptant.Thepresenceofliquidmetalletsintheslagallowsthegeneratedchromiumtodissolveinthepartic

15、les.InthisreactionmodeltheCObubblesarefmedwithintheslagphasethroughthereactionbetweenCO2solidCpresentintheslag.Combiningallthreereactionsthisresultsintheoverallreductionreactionofthemetaloxidesbycarbon(MerepresentsFeCr):

16、MeOxslag(l)x.C(s)?Me(l)x.CO(g)(1)ThepresenceofsolidCintheslagphasecouldhowevernotbeconfirmedbyourmicrostructuralanalyses.ItismostlikelythattheCparticlesreactedwiththeslagbefethesamplecouldbequenched.Thishypothesisissuppt

17、edbythelabatyexperimentsofJietal.[13].Intheirexperimentsittakesabout30secondsfCparticlestoreactalmostcompletelytogaswheninjectedinanEAFslag.InourstudyCO2injectionwasstoppedbecauseofsafetyreasonsbefethewkerenteredthedogho

18、useftakingasample.Thisimpliesthatthetimespanbetweentheendofinjectionthesamplequenchingtakesabout20secondswhichisinthesamederofmagnitudeasintheexperimentsofJietal.TherefeitisbelievedthattheabsenceofCparticlesintheslagsamp

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