外文翻译宝钢碱性氧气转炉炼钢生产及洁净钢控制Word下载.docx
- 文档编号:19729162
- 上传时间:2023-01-09
- 格式:DOCX
- 页数:16
- 大小:99.30KB
外文翻译宝钢碱性氧气转炉炼钢生产及洁净钢控制Word下载.docx
《外文翻译宝钢碱性氧气转炉炼钢生产及洁净钢控制Word下载.docx》由会员分享,可在线阅读,更多相关《外文翻译宝钢碱性氧气转炉炼钢生产及洁净钢控制Word下载.docx(16页珍藏版)》请在冰豆网上搜索。
29ppm,[H]<
1ppminlinepipesteels,and[C]<
16ppm,TO<
19ppm,[N]<
15ppmininterstitialfree(IF)steels.
Keywords:
Cleansteel,Inclusions,Impurityelements,Interstitialfreesteel,Linepipesteel
Introduction
Theimportanceofcleansteelinterrasofproductqualityisincreasinglybeingrecognised.Cleansteelrequirescontrolofthesizedistribution,morphologyandcompositionofnon-metallicoxideinclusionsinadditiontotheamount.Furthermore,sulphur,phosphorus,hydrogen,nitrogenandevencarbon[1,2]shouldalsobecontrolledtoimprovethesteelproperties.Forexample,,formability,ductilityandfatiguestrengthworsenwithincreasingsulphideandoxideinclusioncontents.Loweringthecarbonandnitrogenenhancesstrainagingandincreasesductilityandtoughness.Hardenabilityandresistancetotemperembrittlementcanbeenhancedbyreducingphosphorus.Thedefinitionof'
cleansteel'
varieswiththesteelgradeanditsenduse.Forexample,interstitialfree(IF)steelrequiresbothcarbonandnitrogentobe<
30ppm;
linepipesteelrequiressulphur,phosphorusandtotaloxygen(TO)alltobe<
30ppm,lowhydrogen,lownitrogenandsuitableCa/Sandbearingsteelrequiresthetotaloxygentobelessthan10ppm.[3]Inaddition,manyapplicationsrestrictthemaximumsizeofinclusions[3,4],sothesizedistributionofinclusionsisalsoimportant.
BaoshanIron&
SteelCo.,Ltd(Baosteel)iscurrentlythelargeststeelcompanyinChina.Itsannualsteelproductionwas115milliontonnesin2003,119milliontonnesin2004and14.0milliontonnesin2005.Withregardtothebasicoxygenfurnace(BOF)basedsteelmakingroute,therearethree300tandtwo250tBOFs;
severalsteelrefiningunits,includingoneCAS-OBunit(controlledargonstirring-oxygenblow),twoRH(Ruhrstahl-Heraeus)degassersandoneladlefurnace(LF).Since1990,effortstoimprovesteelcleanlinesshavefocusedondevelopingsteelmakingpracticestolowerTO,N,S,P,HandClevelstoachievelowcarbonaluminiumkilled(LCAK)steel.ForLCAKsteelandIFsteel,theproductionprocessisBOF→RH→continuouscasting(CC),andforlinepipesteel,theprocessisBOF→RH→LF→CC.
Experimentalmethodandexaminationofinclusionsinsteel
Experimentalmethods
Ladlesteelsamplesweretaken500-600mmbelowthetopslagintheladle,tundishsteelsamplesfrom300mmaboveitsoutletandmouldsteelsamplesfrom150mmbelowthemeniscusand300mmawayfromthesubmergedentrynozzle(SEN)outports.Thesamplerwasacylindricalsteelcupwithaconeshapedcoppercovertoprotectitfromslagentrainmentduringimmersion.Attachedtoalongbar,thesamplerwasimmerseddeepintothemoltensteel,wherethecoppermeltedandthecupwasfilled.Smallsteelsamples,80mminlengthand30mmindiameter,weremachinedinto5(dia.)x5mmcylindersforTOandnitrogenanalysis,and20(dia.)×
15mmcylindersformicroscopeexamination.Thesteelpowdersresultingfrommachiningwereusedforanalysisofthecarbon,phosphorusandsulphurcontents.LargeSteelsamplesfromtheladleandtundish,200mminlengthand80mmindiameter,weremachinedinto60(dia.)×
150mmcylinders;
asshowninFig.1.TOandnitrogenmeasurement.Analysisincludedthechemicalcompositionofslagandsteelsamples,microscopeexaminationofmicroinclusions,slimeextractionofmacroinclusionsandSEManalysisofthemorphologyandcompositionofinclusions.
Fig.1Samplinglocationsforcontinuouslycastslab:
TOtotaloxygen
Inthepresentwork,'
macroinclusions'
werethosegreaterthan50umindiameter.Mostoftheseweredetectedintheresiduesextractedbyelectrolyticisolation('
slimetest'
)fromthelargersteelsamples.The'
microinclusions'
dataderivefrommicroscopicassessmentscarriedoutonplanarsections,mostofwhichweresmallerthan~50μm
Morphologyandcompositionoftypicalinclusions
Themorphology,compositionandlikelysourcesoftypicalinclusionsfoundinLCAKsteelsamplesformtheladle,tundishandmoundareshowninFigs.2and3respectively.Themorphologiesincluded:
(a)angularaluminate(Fig.2dandfandFig.3b);
(b)aluminacluster(Fig.2bandc);
and(c)sphericalsilicate(Fig.2aandcandFig.3a).
a.ladle;
b.tundish;
c,d.mound;
e,f.slab
Fig.2Typicalinclusionsfromgivensamplesexaminedbymicroscope
(a)tundish(b)slab
Fig.3Typicalinclusionsfromgivensamplesextractedusingslimemethod
Thepossiblesourcesweredeoxidationproducts,reoxidationproductsorbrokenrefractoryliningbricks.Inlinepipesteel,besidesthesecommoninclusions,manynanoscaleTiNinclusionswerefoundalonggrainboundaries.ThesenanoTiNchangedfromsquaretoellipsoidifcombinedwithTi2O3,asshowninFig.4[5]
a.compoundinclusionswithcompositionTi2O3+MnS;
b.TiNinclusion
Fig.4Nanoprecipitatesinlinepipesteel
Totaloxygenmeasurementisanindirectmethodofevaluatingoxideinclusionsinasteel.3Thetotaloxygen(TO)inthesteelisthesumofthefreeoxygen(dissolvedoxygen)andtheoxygencombinedasnon-metallicinclusions.Freeoxygen,or'
active'
oxygen,canbemeasuredrelativelyreadilyusingoxygensensors.Itiscontrolledmainlybyequilibriumthermodynamicswithdeoxidationelements,suchasaluminium.If[%A1]=0.03-0-06,thefreeoxygenis3-5ppmat1600°
C.Becausethefreeoxygendoesnotvarymuch,thetotaloxygenisareasonableindirectmeasureofthetotalamountofoxideinclusionsinthesteel.OwingtothesmallpopulationoflargeinclusionsinasteelandthesmallsamplesizeforTOmeasurement(normally<
20g),itisraretofindalargeinclusioninasample.Evenifasamplecontainsalargeinclusion,itisprobablydiscountedbecauseoftheanomaloushighreading.Thus,theTOcontentactuallyrepresentsthelevelof<
50umsmalloxideinclusionsonly.ThecurrentTOinIFandlinepipesteelslabsatBaosteelis<
16ppm.TheTOintheladle,tundish,mouldandslabintwotypicalsequencesofLCAKsteelisshowninFig.5,indicatingthattheTOdecreasedfromtheladletothetundish,tothemouldandtothecontinuouslycastslab.
Fig.5Totaloxygeninsteelfromladletoslab
Ladleoperationstoremovemoreinclusions
Ladleslagreductiontreatment
ReoxidationtoformaluminaintheladleduringsteelrefiningismainlycausedbySi02intheslagandliningrefractory,andMnOandFeOintheladleslag,bythefollowingreactions:
3/2(Si02)+2[Al]=(Al203)+3/2[Si]
3(MnO)+2[Al]s=(Al203)+3[Mn]
3(FeO)+2[Al]s=(A1203)+3[Fe]
SlagreductiontreatmentiscarriedoutbyaddingaluminiumandlimeontothetopoftheladleslagtoreduceitsFeOandMnOcontent.TheeffectofladleslagreductiontreatmentontheTOcontentinthesteelisshowninFig.6.AlargerFeO+MnOcontentintheladleslagcorrespondstohighertotaloxygen.Withtheslagreductiontreatment,MnOandFeOintheladleslagwerereducedto<
5%,correspondingto<
20ppmTOinthetundish.
Fig.6EffectofFeOandMnOcontentinladleslagonTOinsteel
Calciumtreatment
Nozzleclogginginducesseriouscastabilityproblemsinaluminiumkilledsteels,suchasloweringthecastingspeed,inducingasymmetricalfluidflowandlevelfluctuationsinthemould,thusentrappingmoreinclusions,andsometimescausingabreakout.Removingmoreinclusionsbeforecontinuouscastingisthebestwaytopreventnozzleclogging,andistheonlyapproachforsteelswithverystrictrequirementsonformability[6].
AtBaosteel,CaSiwireisfedintothemoltensteelduringladlerefining.AluminareactswithCaO,formingcalciumaluminates.Tfthegeneratedcalciumaluminateshavealowmeltingpoint,thencloggingisimproved.ThepossiblecompoundinclusionsgeneratedbycalciumtreatmentincludeCA6,CA2,CA,Ci2A7andC3A,whereCandArepresentCaOandA1203,respectively.Thefirsttwoshouldbeavoidedowingtotheirhighmeltingpointover1700°
C.
CurrentpracticeatBaosteelindicatesthat[Ca]shouldbe>
25ppminordertopreventsolidaluminabasedinclusionclogs.ToomuchcalciumcanalsogenerateCaSwithahighmeltingpoint(2450°
C).ToomuchsulphurinthesteelandtoolowatemperaturealsoenablesCaSgeneration.Baosteelpracticeindicatesthat<
50ppm[Ca]inthesteelcanpreventCaSgeneration,and[Ca]/[Al]>
0.09favourspreventionofnozzleclogging(Fig.17).Hence,[Ca]needstobecontrolledwithintherange25-50ppm,and[Ca]/[Al]>
0-09,toavoidnozzlecloggingproblems.
Controlofnitrogen,carbon,sulphurandphosphorusi
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 外文 翻译 宝钢 碱性 氧气 转炉 炼钢 生产 洁净 控制