177-paper-Analysis of Nature and Source of Micro-i

1AnalysisofNatureandSourceofMicro-inclusionsinTubeBloomandSteelPipesProducedbyHengyangPipeFactoryPENGQichun1，CHENBenqiang1，LIGuangqiang1,WUHanjun1(1.KeyLaboratoryforFerrousMetallurgyandResourcesUtilizationofMinistryofEducation,WuhanUniversityofScienceandTechnology,Wuhan430081,China)SHIShaoqing2,LIYanghua2,XUJingfeng2,PENGZisheng2,SUNQunbao2,NINGJiancheng2(2.HengyangPipeFactory,Hengyang421001,China)Abstract:Thisarticlediscussesthoroughlythequantitativechangeandparticlesizedistributionofmicro-inclusionsinsteelsamplesbeforeLFprocess-LFprocess-VDprocess-tundish-tubebloom-steelpipeinHengyangPipeFactory.Theradialdistributionandquantitychangeofmicro-inclusionsintubebloomandtheradialandlongitudinalsizedistributionandquantitychangealongsteelpipeareanalyzed.Thesourceofmicro-inclusionsisdiscussed.Theresultindicatedthatmeasuresshouldbetakensuchasaddingmoredeoxidizationaluminumdosageandimprovingtundishpowder.Keywords:compactprocess;micro-inclusions；roundbillet1IntroductionTheEAF-LF/VD-HCCprocesssysteminHengyangPipeFactoryisapipeproductionlinethathasthespecialcharacteristics.Itplacesstrictrequirementonthemoltensteelquality.Thisprocessaffectstheformationofthemicro-inclusionsinthemoltenandthesize,mechanicalbehavior,andthedispersionoftheinclusionscloselyaffecttheproductquality[1-2].Therefore,asystematicstudyisconductedontheprocessmicro-inclusionsbehaviorinordertoguidetheproductiontooptimizethecontroloftheinclusionstoobtainhigh-qualitytubebloom.2Experimental2.1Steel-makingprocessHengyangPipeFactoryhasahorizontalcontinuouscastingproductionlineinsuccession,adoptingwiththeEAF-LF/VD-HCCcompactprocesstoproduceroundbillet.Ladlerefiningfurnace,VDvacuumdegassingplant,wirefeederandsoonrefinefacilityareappliedinsecondaryrefining.Argonblowingintheentireprocessandprotectivecastingareappliedintheladle.22.2ExperimentalprogramSteelandslagweresampledinEAFend-point,beforeandafterladlerefiningtreatment,tundish,CCbilletandsteelpipe.Tracermethodisappliedinthisstudytoidentifythesourceoftheinclusionsinthesteel.Chemicalanalysis,metallographicmicroscopeobservation,SEM,andEDXspectrumanalysisareusedtoacquiretheinclusions’composition,sizedistributionandthemechanicalbehaviorduringtherollingprocess.3Experimentalresultsanddiscussions3.1ThevariationofinclusionsintheprocessesTable1Theparticlemicro-inclusionsizedistributioninexperimentalheatateachprocess(%)ProcessNumbers(1/mm2)10μm10-15μm15-20μm20μmLF1010.8575.4617.044.542.96AfterLF8.4868.6219.497.794.07AfterVD8.9371.8417.286.194.66Tundish15.6382.611.533.232.64Tubebloom16.0583.3410.343.932.39Steelpipe16.2580.329.954.625.11（LF10meanstreatedinLFfor10minutes）Theaveragenumberchangeofmicro-inclusionsintestingheatineveryprocessisshowedinFig.1.(1/mm2)10.858.488.9315.6316.0516.2505101520LF10AfterLFAfterVDTundishTubebloomSteelpipeDensityofinclusions(1/mm2)Fig.1Theaveragenumberchangeofmicro-inclusionsinexperimentalheatforeachprocessDrawnbythetestdata,after10minutesLFtreatment,theaveragenumberofmicro-inclusionsis10.85piece/mm2andtheaveragenumberis8.48piece/mm2afterLFtreatment.Itisevidentthattheeffectofremovingmicro-inclusionsbyLFrefining3isgood.FromLFtoVD,thenumberofthemicro-inclusionsincreasedslightly.Thisincreaseisrelatedeithertotheoperationalprocess,ortotheeffectofinsufficientvacuumingortotheinsufficienttimeofvacuuming.Consequently,theproductionfacilitymanagementshouldbeenhancedtoinsuretheproperVDtreatmentconditionandsufficienttimeofvacuumingprocess,whichinturnwouldimprovetheremovalofmicro-inclusionsinVDprocess.010203040506070809010μm10-15μm15-20μm20μmThepercentageforinclusionswithdifferentparticlesize/%LF10AfterLFAfterVDTundishTubebloomSteelpipeFig.2Theparticlesizedistributionofmicro-inclusionsforeachprocessFromLF(orafterVD)totundishstage,thenumberofmicro-inclusionsincreasedsubstantially,whichindicatestheoxidesintheliningandslagdecomposedandemittedoxygenintomoltensteel,thereforecontaminatedthemolten.Thenumberofmicro-inclusionsinsteelslightlyincreasedfromtundishstagetotubebloomstage,indicatingthateitherthemoltenwasnotinsulatedwellfromairandwasre-oxidizedortherewastundishpowderentrapment[3-4].Becauseoftherelativelylowdepthofmoltensteelinthetundish,largeamountoftundishpowdercarryover,lowabilityofabsorbingmicro-inclusionstheprotectiveslaginthetundish,powderentrapmentandre-oxidationwererelativelysevereandtheamountofmicro-inclusionsinsteelincreased.Fromtubebloomstagetosteelpiperollingstage,someinclusions(suchasMnSandAl2O3)aredeformedorcrashedbyrollingstress,andsothenumberofinclusionsslightlyincreased.Theamountandsizeofthemicro-inclusionschangedinrespectthattheinclusionsaregoingfloatingupinsecondaryrefiningandcasting,whiletheoutsideinclusionsare4enteringintothemoltensteel,thechangeisshowedintable1andFig.2.Thefloatingspeedofstaticmicro-inclusioncouldbecalculatedbyStokes'formula[5].mppmpgdu18/2(1)Intheposture:pu——Thefloatingspeedofinclusion/cm﹒s-1;m，p——Densityofmoltensteelandinclusionrespectively/g﹒cm-3;g——Gravitationalacceleration/dyn﹒g-1;m——Viscosityofliquidsteel/g﹒(cm﹒s)-1;pd——Diameteroftheinclusion/cm.K