宝钢低夹杂物精炼

-1-PROGRESSOFPRODUCTIONTECHNOLOGYOFCLEANSTEELINBAOSTEELCUIJianZHENGYiyuZHULixin(BaoshanIronandSteelCo.,Ltd.)Abstraca:Theprogressincontroltechnologyofcarbon,nitrogen,totaloxygen,phosphorus,andsulphuraswellasinclusionsinsteelisdiscussedatBaosteel.ThepurityobtainedinIFsteelandpipelinesteelisintroduced.Keywords:Cleansteel;IFsteel,Pipelinesteel,Steelmaking1PrefaceTheso-calledcleansteelgenerallyisthesteelinwhichthecontentofimpurityelements,suchasphosphorus,sulphur,totaloxygen,nitrogen,hydrogen(includingcarbonsometimes)andinclusions,shouldbeverylow.Theso-calledimpurityelementscanchangewithdifferentgradesofsteel.Oneelementisakindofharmfulimpurityincertainsteelgrade.Itmaybenotharmfulenough,evenmaybeusefulinanothergrade.Inotherwords,thecontrolelementsaredifferentfordifferentperformancedemandsofsteel.ForIFsteel,thecontentofcarbon,nitrogen,totaloxygenandinclusionsinsteelshouldbeaslowaspossibleinordertogaingoodstretchability,highrvalue,perfectsurfacequalityandreducetheamountofthemicro-alloyelements.Thehighqualitypipelinesteelshouldhaveultralowsulphur,lowphosphorus,lownitrogen,lowtotaloxygencontentandacertainratioofCa/S.Sincethemiddleperiodof1990’s,Baosteelhasendeavoredtodevelopthemeltingtechnologyofcleansteel.Theresearchworkconcentratesonthedevelopmentofrelativelyindividualtechnologiesandmassproductionofhighcleanlinesssteel(IFsteel,pipelinesteeletc.).ThispaperpresentstheprogressofproductiontechnologiesofcleansteelinBaosteel.2Progressofindividualproductiontechnologyofcleansteel2.1Productiontechnologyofultra-lowsulphursteelThedesulphurizationinhotmetalisakindofeconomicalandeffectivedesulphurizationmethod,whichhasbeenwidelyusedinsteelmakingproduction.Twokindsofdesulphurizationpatternsintorpedocar(CaObasedflux,CaC2basedflux)andhotmetalladle(Mgbasedflux)weredevelopedinBaosteel.Whentheoriginalsulphurcontentisbetween150ppm(1ppm=10-6)and300ppm,thesulphurcontentofhotmetalcandecreaseto10ppmto30ppmafterthedesulphurization.ItiswellknownthatdesulphurizationabilityofBOFisfairlylimited.Whentheoriginalsulphurcontentofhotmetalisverylow,thesulphurpick-upphenomenoninBOFoftenoccursbecauseoftheadditionoflimeandscrapwithhighersulphurcontent.In-2-general,itisdifficulttoproducethesteelsteadilywithsulphurcontentlessthan30ppmonlybyhotmetalpretreatment.SotodevelopedesulphurizationtechnologyofmoltensteelaftertappingisnecessaryThreekindsofdesulphurizationpatternsinrefiningstagehavebeendevelopedoneafteranotherinBaosteel.Theirbasicfuturesareasfollows:(1)DesulphurizationpatternofaddingdesulphurizerinRH(patternA)DevelopthehigheffectualCaO-CaF2baseddesulphurizer,Adddesulphurizertovacuumvesselthroughalloychute,Controltheamountofcarry-overslagofBOFaslowaspossible,andcarryouttheladleslagconditioning.(2)DesulphurizationpatternofpowderinjectioninRH(patternB)DevelopCaO-Al2O3basedpremelteddesulphurizer,Adaptalowlancepositiontomakepowderintomoltensteelfully,Carryoutdeoxidationofmoltensteelandladleslag.(3)DesulphurizationpatterninLF(patternC)DevelopCaO-Al2O3baseddesulphurizer,Optimizedeoxidationpatternofslag,Adaptstrongstirringpatternsoastopromotethereactionbetweenslagandmoltensteel.TheresultsofindustrialdesulphurizationtrialareshowninTable1.Table1ResultsofdesulphurizationtrialPattern[S]i/ppm[S]f/ppmDe-Srate/A28.416.243.0B61.935.842.2C67.08.787.0[S]i:originalaveragesulphurcontent[S]faveragesulphurcontentafterdesulphurizationItcanbeseenfromTable1,thedesulphurizationratesareabout40%fordesulphurizationpatternsinRH.Thesekindsofpatternsaresuitableasthecompensationmeansofsulphurcontentcontrol.Atthesametime,itcanbeseenthatthedesulphurizationpatternsinLFhaveveryhighdesulphurizationrate,andtheaveragedesulphurizationratereaches87%.Thesulphurcontentinmoltensteelcanbebelow10ppmandtheaveragecontentis8.7ppm.2.2ProductiontechnologyoflowphosphorussteelInBaosteel,thefollowprocesstrials,whicharecorrelatedwiththephosphoruscontrol,havebeenresearched.(1)Hotmetalpretreatment(De-Si,De-P,De-S)+BOFprocesswithsmallslagvolume(slagvolumeindex=0.3)--(patternA).(2)Hotmetalpretreatment(De-S)+BOFprocesswithlargeslagvolume(slagvolumeindex=1.0)--(patternB).(3)Hotmetalpretreatment(De-Si,De-P,De-S)+BOFprocesswithlargeslagvolume(slagvolumeindex=1.0)--(patternC).(4)BOFpretreatment(De-P)+BOFprocesswithmiddleslagvolume(slagvolumeindex=1.0)--(patternD).-3-ThedephosphorizationresultsofabovepatternsshowinFig.1AsshowninFig.1,theaveragephosphoruscontentsobtainedbyusingpatternCandpatternDarerespectively66ppmand58ppm.ThereforethepatternCandpatternDarealltheeffectiveproductionprocessforlowphosphorussteel.2.3ProductiontechnologyoflowoxygensteelAseriesofmeasuresaimingatreducingAl2O3inclusions,totaloxygencontentandpreventingfromslagentrapmenthavebeenadoptedforlowoxygensteel(suchasIFsteel)inBaosteel.Useslagstoppertocontroltheslagthicknessatlessthan70mminladle.Ladleslagconditioning:addAldrossonslagtodecreaseT.Fecontentduringturndown.Control[O]atRHdecarburizationendandcirculationtimeafterRHdecarburization.Adopttundishpurificationtechnology.Useahighviscositymoldpowdertopreventfromtheentrapment.MaintainreasonableArfl