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1、ChromiumRecoveryduringEAFStainlessSteelRefiningGUOMuxing1DURINCKDirk1JONESPeterTom1HEYLENGert2HENDRICKXRoel2BAETENRik2BLANPAINBart1WOLLANTSPatrick1(1.DepartmentofMetallurgyMaterialsEngineeringKatholiekeUniversiteitLeuven

2、KasteelparkArenberg44BE3001Heverlee(Leuven)Belgium2.UgineCrrecoveryIndustrialexperimentsSlagbasicity0IntroductionBothfeconomicenvironmentalreasonstheCrOxlevelsinthefinalElectricArcFurnace(EAF)stainlesssteelslagsshouldbem

3、inimised.AsubstantialnumberoflabatyinvestigationshavebeenpublishedonCrOxreductionreactions[14].HoweveralargegapexistsbetweenthesimplifiedexperimentalconditionsthecomplexconditionsintheEAFsystem.Theliteraturealsoprovidesm

4、anyindustrialstudiesdealingwithimprovingCrrecoverybyavarietyofmethods[59].Neverthelessingeneralonlyfewindustrialtestrunshavebeendescribedintheopenliterature.InmostcasesthediscussiononCrrecoveryremainsratherqualitative.Th

5、ispaperperfmsanobservationalstudyon36austeniticheatsfromtwodifferentEAFinstallations.SlagsamplesarecollectedatdistinctprocessstagesareanalysedwithEPMAEDSprovidingbothcompositionalmineralogicaldata.Combinedwithstatistical

6、methodsthedatabaseallowsfananalysisofthethermodynamicskiicsoftheCrrecoveryprocess.ThegoverningEAFprocessparametersarequantitativelydeterminedpracticalguidelinesareproposed.1Experimentalmethods1.1IndustrialpracticeTheCrre

7、coverystudywasperfmedinU&ABelgium(Genk).ThemeltshopofthisstainlesssteelcompanyconsistsoftwoEAFunits(‘EAF1’‘EAF2’)withacapacityof120tonnes.EAF1isanexcentricbottomtypefurnacewherenoslagfoamingpracticeistargeted.EAF2isaconv

8、entionalspouttypefurnacewithanexchangeablerefractyvesselisequippedwithaCO2lance.TheoperationalpracticefEAF2isasfollows.Afirstbucket(6070tonnes)ofsteelscrapisloadedtogetherwithFeCr(with4to5wt%Si).FeSilimedolomiticlimearea

9、lsoadded.Afterthefirstloadhasbeensufficientlymoltenasecondbucketofscrap(50tonnes)isaddedtogetherwithFeCralloys.MeFeSiissubsequentlyloaded.AssoonasthesteelloadisliquidtheinjectionofCO2commences.TheCO2blowingenhancesthewhe

10、reBisthebasicityoftheslagexpressedastheCSratio(i.e.CaOSiO2alloxidesinwt%).HoweverfmanyEAFpracticesthereisaconsiderabledifferencebetweentheequilibriumresultstheactualindustrialdata.Thisisduetothefactthatthereductionreacti

11、on(Eq.(1))doesnotnecessarilyreachequilibrium(seealso[1011]).Figure2EvolutionofCr2O3contentduringEAFprocess[Cr2O3expressedas?wt%Cr2O30?1].2.2ChromiumoxidecontentevolutionfinalvaluesTheevolutionofthetotal‘Cr2O3’contentinth

12、eslagisshowninFig.2frepresentativeheats.DuetoreasonsofconfidentialityCr2O3levels(expressedinwt%)aregivenasrelativevaluesbwithbbeingequalto?timestheactualCr2O3concentration(?isafixednumberbetween01).Fig.3providesbackscatt

13、eredelectronimagesofconsecutiveslagsampleshighlightingtheevolutionoftheslagmicrostructureduringtheprocess.EspeciallyintheinitialstagesoftheprocessalargefractionoftheslagconsistsofsolidMgO.(CrAl)2O3spinelphases.Expressedi

14、nat%atypicalspinelcompositionis:14%Mg23%Cr5%AlwithminamountsofFeMnCa.Fig.2showsthatduringtheblowingperiodtheCr2O3levelintheEAF2slaginitiallyrisesthensagain.Duringthefirsthalfoftheblowingperiodthelessstableoxidesintheslag

15、suchasFeOarereducedbytheinjectedCtheSidissolvedinthesteel.AtthesametimetheinjectedO2mainlyreactswithmetallicCrSitofmCr2O3SiO2.Theseoxidationreactionscontinueduringthesecondhalfoftheblowingperiodwhichisinitiatedassoonasth

16、eFeOlevelintheslaghasbeendepleted.AtthatmomenttheCinjectionleadstothereductionofCrOxbySidissolvedinthesteel.OntheotherhitisbelievedthatinthisblowingperiodCrOxisalsoreducedbytheinjectedC.Howevertheoccurrenceofthisreaction

17、issomehowdisputedintheliterature.TheexperimentsofKerrFruehan[12]suggestthattherateofthereductionreactionistooslowtoobservealargeintheCrOxlevels.GrnerupJacobsson[7]howeverpointoutthattheobservedslowreactionrateintheseexpe

18、rimentsiscausedbytheneedfsolidCrnucleationassociatedwiththereactionbetweenCrOxC.WhenaliquidmetalphaseispresentinthesystemthemetallicCrcandissolveinthemetalwhichrelievesthekiicbarrierenhancesthereductionreaction.Fromthisp

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