球铁过程中Mg 的吸收率提高方法

Y:\Presentasjoner\NewPresentationFolder\MgTreatment\English\Papers\RecoveryofMginaDuctileIronProcess.doc09.01.06eghRECOVERYOFMAGNESIUMINADUCTILEIRONPROCESS.S.O.OlsenandC.HartungElkemFoundryProducts,Kristiansand,NorwayAbstract.Residualmagnesiumandmagnesiumrecoveryhavealwaysbeensubjectsfordiscussionsamongstfoundrypeople.Thispresentationsummarisesthemostimportantfactorsthatwillinfluencetherecoveryandadditionrateofmagnesiuminladletreatmentprocesses.FactorsinfluencingtheMagnesiumRecoveryandAddition.SulphurandOxygeninBaseIron.Inordertoevaluatethebasicsofductileironproductionthegrowthmechanismofthegraphitehastobeconsidered.Itisproposedthatgrowthnormallyoccuralongthepoleoftheplanewiththelowestinterfacialenergyincontactwiththemelt.Thiswillbetheplanewiththehighestpackingdensityandthiswillhavethehighestgrowthrate.WithsurfaceactiveelementslikeOandSpresenttheprismplanewillgrowfastest,buttheseelementsareneutralisedthebasalplanwillagainhavethehighestgrowthrate.Thehighestgrowthratefromthebasalplanewillresultinductileironandfromtheprismplaneingreyiron.Hencemagnesiumisaddedinordertoneutralisesurfaceactiveelementssuchassulphurandoxygen.Thismeansthatincreasedcontentofsulphurandoxygeninbaseironrequirehigheradditionofmagnesium.(Fig.1.)AnexampleshowingtheeffectofhighersulphurlevelinthebaseironwithoutincreasingtheadditionrateofMgFeSiispresentedinfigure2.FoundryProductsDivision©Elkem17.July2003PresentationTechnicalInformationSheet23SOcontentinbaseironSOcontentinbaseiron%Mg%S%OInBaseMetalHighSOBaseMetal·IncreasedMgAdditionSOaresurfaceandinterfaceactiveelementsandhavetobeneutralisedFigure1:Increasedcontentofsulphurandoxygeninbaseironrequirehigheradditionofmagnesium.FoundryProductsDivision©Elkem17.July2003PresentationTechnicalInformationSheet23BaseS=0.018%1.0wt%MgFeSiFinalS=0.016%Nodularity∼50%BaseS=0.010%1.0wt%MgFeSiFinalS=0.010%Nodularity∼80%MagnesiumMagnesiumvsvs.Sulphur.SulphurExample:BaseMetalSulphurContentExample:BaseMetalSulphurContentFigure2:Showsanexampleoftheeffectof2differentScontentsinbaseironatthesameadditionrateofMgFeSialloy.The0,018%Sgives50%nodularitywhilethe0,010%Sgives80%nodularity.Figure3showstherelationbetweenSinbaseironandtheminimumresidualMgthatisrequiredtogiveductileiron.Figure3.Schematicrepresentationoftherelationbetweenbaseironsulphurcontentandrequiredresidualmagnesiumtoproduceductileiron.TappingTemperature.Tappingortreatmenttemperatureshouldbekeptaslowaspossibleinordertoavoidexcessivereactionviolence.Thehigherthetemperature,themorevaporisationandlowerrecoveryofMg.TheboilingpointofpureMgisabout1110°Candthenormaltreatmenttemperatureinafoundrywillbecloseto1500°C.NodulariserMgFeSiadditiontoladle.Thetimebetweenmagnesiumadditionandtappingshouldbeminimisedtopreventpreheatingandoxidationofthealloy.AtthesametimethereshouldbenoliquidmetalresidualfromprevioustreatmentsintheladleasthismaystarttoreactwiththealloyandleadtolowerrecoveryofMg.Slag.Slagcarryoverfrommeltingandholdingfurnacesintothetreatmentladleshouldbeavoided.Slagthatistransferredfromfurnacetotheladlewillreactwithmagnesiumandreducerecovery.Properseparationprocedurestominimiseslagcarryoverneedtobeinplace.Normallythefurnaceisproperlyskimmedbeforethefirsttreatment,butthenexttreatmentswillsufferfromslagcontamination.LadleDesign.TheratioofinternalHeight:Diametershouldbeatleast2:1andthereshouldbeanalloypocketbigenoughtocarrythealloyandcoveringmaterial.TheMgrecoverywillincreasewiththeheightoftheladlebecauseweincreasetheferrostaticheadbeforethereactiontakesplace.FoundryProductsDivision©Elkem17.July2003PresentationTechnicalInformationSheet23LadleDesignLadleDesign·HighRecovery·ConsistentReproducability·Reliable·NoFlare·90%FumeReduction·NoMetalsplashing·MinimumCandTemperaturelosses·GoodEconomy5080%MgRecovery!Agooddesignedladlegivesthefollowingadvantages:Figure4:Ladledesigncriteriawiththeadvantagesofagoodladledesignindicated.Theladleshouldalsobeproperlyinsulatedtominimiseheatlossesandconsequentlytherequiredtreatmenttemperature.Atundishcoverlidisalsohighlyrecommendedformagnesiumandtemperatureyieldreasons.AlloyCover.Analloycover(sandwichcover)intheladlewilldelaythereactionstartandgivebetterabsorptionofmagnesiumintotheliquidiron.AscoverafinesizedFeSiareoftenused,butalsosteelplatesordrycastironturningscouldbeused.Theimportantthingistouseacoverandnotsomuchwhattypeofcoverisused.FillingTime.Fillingrateshouldbehighinordertoachieveahighferrostaticheadintheladlebeforethereactionstarts.Ashortfillingtimewillalsoleadtoreducedtemperaturelossandevaporation.ChemicalCompositionofNodulizer.Highmagnesiumcontentinthealloywillgiveamoreviolentreactionandreducedrecovery.Highcalciumcontentwillreducethereactivityandincreasethemagnesiumrecovery,butitwillalsoincreasethetendencytoslagformation.Therareearthmetals(cerium)willassistingivingabetterrecoverybecauseitallowsforworkingatlowermagnesiuminthealloyandlowerresidualmagnesiumintheiron.Aluminiumshouldbekeptlowinthealloyinordertoreducetendencytoslaganddrossformation.AlloySizing.Awidealloysizinggivesdensebulkpackingintheladlechamber.Thealloywillthenfuseandreactslowlyinacontrolledmannerwithaminimumofpiecesescaping.Piecesfloatingandburningonthesurfaceareawaste.Howevergrainsegregationshouldbeavoidedsincethiscancauseinconsistencyintheproduction.Recommendedsizingforsmallladlesis1–10millimetresandforbiggertreatments4–32millimetres.PouringTime.Longpouringtimesrequirehigherinitialresidualmagnesiuminordertocompensateforfadinglossesduringtime.Thismeansincreasedalloyadditionandagainreducedmagnesiumrecovery.Higheradditioningeneralwillgivelowerrecovery.Inoculation.Withagoodinoculationlessresidualmagnesiumisrequiredtogivegoodnodularity,andasaresultaloweralloyadditioncanbeusedandtherebyabetteralloyrecoverycanbeachieved.InmanycasespoornodularityordegenerationofgraphitenodulesisincorrectlyattributedtolowresidualMglevelswhenthecauseisreallyinsufficientinoculation.SlaginLadleandAlloyPocket.Slagbuildingupintheladleandalloypocketleadstoreducedmagnesiumrecovery,probablyduetoreactionsbetweentheslagandmagnesium.Overspillofalloywilloccurifpocketisallowedtofillwithslagandthiscanleadtofloatationofalloy.Ladlesshouldbekepttiltedwhenemptytoavoidslagcloggingthealloypocketandladlewalls.StorageofFoundryAlloys.Allfoundryalloyswillcontainacertainlevelofreactiveelements.Thesereactiveelementsarenecessaryinordertogivethewantedeffect.Thismeansthatfoundryalloyswilloxidiseifexposedtomoisture.Oxidisedalloyswillgivealowerrecoverythanfreshmaterialsandheavyoxidationcanresultinupto50%reductioninthemagnesiumrecovery.Containersofalloyshouldbestoredinadryplaceandnotbeopeneduntilrequiredatthetreatmentstation.Largechangesintemperatureshouldalsobeavoidedinordertominimiseriskofcondensationandtransportationshouldbedoneinclosedandwatertightunits.ExamplesofhowdifferentFactorscaninfluencetheMgFeSiAddition.RequiredMgFeSiadditionwt%1480°C1460°C1520°C5min2min30scleanfurnacesomelotof1:11:1,51:3freshsomegoodCa=0,5,Re=0,5Ca=0,5Ca=2,5Ca=1,0Ca=2,5Re=1,5S=0.006S=0.01S=0.016Sulphurcont.Tappingtemp.TimebetweenMgFeSiadd.andtappingLadledesigndiameter:heightSlaginfurnace.AlloyCoverChemicalcompositionofMgFeSi1.51.61.41.81.71.31.21.9OxidisedMgalloy.heavysomenoneFigure5:ThediagramshowssomeexampleshowdifferentfactorscaninfluencetheMgFeSiadditioninaductileironladletreatmentprocess.ResidualMagnesiumandFading.Thetotalanalyticalorresidualmagnesiumcontentofliquidironimmediatelyaftertreatmentiscomprisedof:DissolvedmagnesiumMicroinclusionsofmagnesiumcompoundsLargermagnesiumcontainingslagparticlesFigure6:Fadingofmagnesiumduringholdingoftreatedductileiron(left),andschematicrepresentationofmagnesiumlossesfromatreatmentladle(right).Thesecontributionstototal(residual)magnesiumwillreactindifferentwaysduringsubsequentholdingoftheiron.TheslagparticleswillfloataccordingtoStokesLawandmovetothesurface.Analyticallywewillseethiseffectasafadingofresidualmagnesium.Inordertouseresidualmagnesiumascriteriaforacceptancethereshouldbeaverystrictsamplingprocedure.Onlyifsamplesaretakenthesamewayeverytimewillitbepossibletocomparetheresults.References.1.T.Skaland:Amodelforthegraphiteformationinductileiron,Ph.D.Thesis1992:33,TheNorwegianInstituteofTechnology,Trondheim,Norway(1992).2.R.Elliott:CastIronTechnology,1988,London,UK,Butterworths.3.S.I.Karsay:DuctileIronIProduction,QIT19764.M.Onsøien:Microstructureevaluationinductilecastironcontainingrareearthmetals,Ph.D.Thesis1997:115,TheNorwegianInstituteofTechnology,Trondheim,Norway.5.J.Nilsson:Slagginnesluningerisegjarnochgråjarn,Rapport921209,SvenskaGjuteriforeningen,Jønkøping,Sweden.6.Gjutfelsanalys(Handbok).Mekanpublikasjon76201.SverigesMekanforbund,19767.ElkemTechnicalInformationSheets RECOVERYOFMAGNESIUMINADUCTILEIRONPROCESS. Abstract. FactorsinfluencingtheMagnesiumRecoveryandAddition. SulphurandOxygeninBaseIron. TappingTemperature. NodulariserMgFeSiadditiontoladle. Slag. LadleDesign. AlloyCover. FillingTime. ChemicalCompositionofNodulizer. AlloySizing. PouringTime. Inoculation. SlaginLadleandAlloyPocket. StorageofFoundryAlloys. ExamplesofhowdifferentFactorscaninfluencetheMgFeSiA ResidualMagnesiumandFading. References.