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Rolerole,Role,ROLE

    Role

JoURNALOFRREEARTHS

    ;Vo1.21,No.1,Feb.2003,P.81

    ;RoleofRareEarthinLowSulphurNb-?Ti-?BearingSteel

    ;ZhuXingyuan(朱兴元)’,?nQin(林勤),ZengJing(曾静).,LiuJixiong(刘继雄).,

    ;GaoPingxiang(高平祥),WangYaohua(王跃华)

    ;(J.WuhanUniversityofTechnology,Wuhan430070,China;2.PhysicalChemistryDepartment,Universityof

    ;ScienceandTechnologyBeijing,Beijing100081,China;3.CenterofWuhanIronandSteelCompany,Wuhan

    ;430080,China;4.RailwayEngineeringEquipmentandMaterialsWorksofWuhanIronandSteelCompany,Wu

    ;han43oo83.China,)

    ;Abstract:Theeffectofl’al~earthoilthemicrostructures,mechanicalpropertiesandinclusionsinlowsulphurNb-Tibear

    ;ingsteelwereinvestigated.Itisshownthatthetransverseyieldpoint,thetraversetensilestrengthandelongationoftest

    ;ingsteelsdecreaseinitiallyandthenrisewithincreasingcontentofrareearth.Theimpactenergyvaluesofthetesting

    ;steelsexhibitacontrarytrend.Properamountofrareearthinthesteelscanimprovetheanisotropyofimpacttoughness

    ;above20?

    anditdoesnotaffectthetypeofmicrostructureswhichfilestillcomposedofferritesandpearlites,butthe ;pearliteamountincreases.Ononehand,Hu?

    earthcleansthemoltensteelandreducestheamountofinclnsions;onthe

    ;otherhand,rareearthmakestheinclusionsspheroidizd,refinedanddispersed,andthusimprovesthedistributionofin

    ;chsions.

    ;Keywords:metalmaterials;Nb-Ti-bearingsteel;property;micmstructure;inclusion;rareearths ;CLCnumber:TG142.33;TG146.45Documentcode:AArticleID:10020721(2003)01008105

    ;Theplicationofrareearthinsteelisdevelop

    ;ingrapidlybecausetheyieldofrareearthsteelsin

    ;Chinahasexceeded60I)000t.Therolesofrareearth

    ;insteelsincludethreeaspects.First,cleaningmolten

    ;stee1.Itdeoxidizesanddesulfurizesanddecreasesthe

    ;amountofinclusions.Itreducesthedetrimentaleffect

    ;ofph(o.

    ;phorus,sulphur,arsenic,antimony,bismuth,

    ;lead,tinetc.Second,spheroidizingtheinclusions.It

    ;modifiesthemorphologyandnatureofinclusions.

    ;,I1llird.micro.alloyingeffect.Itincludesinteractions ;thcarbon,nitrogen,hydrogenandotheralloyingel

    ;ements.solidsolutioninsteelsandeffectsontheso

    ;lidification,grainboundary,phasetransformationand ;microstructureetc.As1Sl=0.015%orso,themain ;roleofrareearthistointeractwithsulphur.takingthe ;ratiobetween[RE]andlS]asthemaincontrolling ;parameter.Withthedevelopmentofsteelmakingpro

    ;cesses,thecontentsofoxygenandsulphuraredeclin

    ;ingcontinuously,sothemicroalloyingeffectofrare

    ;earthinthesteelbecomesmoreandmoreimportant. ;Recently,manyinvestigationshavebeenmadeonthe ;roleofrareearthandmicro.alloyingelementssuchas ;niobium.vanadiumandtitaniumetc.insteels9J.

    ;However.theinteractionsbetweenrareearthandmi

    ;croalloyingelementshavenotbeeninvestigatedwhen ;niobiumandtitaniumareaddedsimultaneously,espe. ;ciallyinlowsulphurmoltenstee1.FormakingfuUuse ;ofChineseresourcestodevelopthemicroalloying ;steelswithrareearth,itisverynecessarytoinvesti. ;gatetheinteractionmechanismbetweenrareearthand ;niobiumandtitanium.,I1llispaperintendstoinvesti. ;gatetheinteractionofrareearthwithniobiumandtita. ;niuminlowsulphurNbTibearingstee1.tofindthe

    ;effectsofrareearthoncaststructure,microstructure ;andmechanicalpropertiesandtheeffectofrareearth ;oninclusions.

    ;1.1Refiningoftestedsteels

    ;Thetestedsteelswererefinedbya50vacuum ;inductionfurnace.Therefiningcrudematerialswere ;lowsulphurindustrialpureirobwiththechemical ;compositions(massfraction,%):C<0.03,Si0.19, ;MnO.24.PO.018andS<0.o05.Pureceriammetal ;(ceriumcontentismorethan99%)wasselectedas ;rareearth.Attheendofrefining,themoltensteel ;wasdeoxidisedbyaluminumandrareearthwasadded ;Receiveddate:200l09l7:reviseddate:20020326

    ;Foundationitem:ProjectsupportedbytheNationalItemsof8.5Pect

    ;BiographyZhuxingyuan(1964),Male,Doctor,Associateprofessor ;*CommOo~author(Email:zxyzxy@public.wh.hb.cn) ;

    ;beforetapping.A50kgingotwascastforeverytest

    ;ingladle.’Thechemicalcompositionswereanalyzed

    ;bytwosamplestakenfromdifferentpositionsofthein

    ;gottoensuretheaccuracy.Theanalysisresultsare ;showninTable1.

    ;1.2Analysismethodsoftestingsteels

    ;Themechanicalpropertiesoftestingsteelswere ;measuredbyWE6Otensiletestingmachine.Thesize ;oftestingsamplesis8mm×40min×210mm.The ;impactpropertiesoftestingsteelsatthetemperature ;rangefrom20to78oCweretestedbyJB30Bim

    ;pacttestingmachine,andthetestingsamples,witha ;sizeof5mln×10mln×55mm.werecharpyVshape

    ;notched.ThemicrostructureswereobservedbyMM6 ;orOLYMPUSPME3opticalmetallographicmicro

    ;scope.Themetallographicsamplesweremechanically

    ;preparedandtheetchantwasnita1.Quantitativemet

    ;allographicanalysiswasconductedonIBAS--2000im-- ;ageandanalysissystemtodetermineandmeasurethe ;morphology,sizeandareaofinclusions,andthearea ;andsizeofpearlites.

    ;1.3Rollingoftestingsteels

    ;The50kgroundingotswerereheatedforabout ;twohsat1200oC.Twostagecontrolledrollingwas

    ;carriedoutbyaminirollingmil1.Theinitialrolling ;temperaturewasabout1150oC;therollingtempera

    ;tureregionwithrecrystallizationwas10001150?.

    ;JoURNALOFRAgEEARTHS,Vol21,No.1,Feb.2003 ;2ResultsandAnalysis

    ;2.1EffectsofREonmechanicalproper-

    ;tiesoflowsulphurNb?-Ti?-bearing

    ;steel

    ;Effectsofrareearthonyieldstrengthandten

    ;silestrengthoflowsulphurNb--Ti--bearingsteel ;Figs.1and2illustratetherelationshipbetweenrare ;earthcontentsandtransverseyieldstrengthaswellas ;tensilestrengthoflowsulphurNbTibearingstee1.It

    ;canbeseenthatboththetransverseyieldstrengthand ;tensilestrengthdecreaseinitially,andthenriseobvi

    ;ouslywithincreasingcontentofrareearth.eeffects

    ;ofrareearthonstrengthhavetwosides.Ononehand, ;rareearthcleansthemoltensteel,whichhasaninter

    ;actionwithnitrogenorphosphorusanddecreasesthe ;quantityofpearlite.Thisleadsthestrengthtoreduce. ;Ontheotherhand,rareearthissolidsolvedintothe ;steel,whichdecreasesthethicknessofpearlitelame1. ;1aes,andrefinesthegrainsandacceleratestheprecip

;itationofcarbonitrides.Thisincreasesthestrength….

    ;2.1.2Effectsofrareearthonelongationinlowsu1. ;phurNbTibearingsteelFig.3showstherelation

    ;shipbetweenrareearthcontentandtheaveragetrans. ;verseelongationinlowsulphurNbTibearingstee1.It

    ;canbeseenthatthetransverseelongationdecreases ;initiallyandthenrises.

    ;2.1.3Effectsofrareearthonimpactenergyinlow ;andtherollingtemperatureregionwithoutrecrystalli--sulphurNb--Ti--bearingsteelTable2showsthea

    v--

    ;zationwas800950oC.Fortwostagecontrolledroll

    ;ing,repetitivedeformationwasfirstappliedonthe ;testingsteelsintherecrystallizationtemperatureregion ;toproducefinerecrystallizationygrainswiththeaid ;ofmicroalloyingelements,niobiumandtitaniumor ;theirprecipitates,whichprohibitsrecrystallizati ;Then,multipassdeformationwasimposedonthefine ;grainedausteniteinthenon--recrystallizationtempera-- ;tureregionbeforetheaphasetransformation. ;Thus,alargeamountofnucleationsitesfora

    ;phasetransformationwascreatedandfineferritegrains ;couldbeobtainedtoimprovethestrengthandductility ;oftestingsteelsl.’.

    ;eragetransverseimpactenergyvaluestorvanousrare ;earthcontentsatdifferenttemperatures.TheCOITe

    ;spondingcurveoftransverseimpactenergyat20?

    ;isshowninFig.4.Itcanbeseenthatthetransverse ;impactenergyValuesriseinitiallyandthendecrease ;withincreasingofrareearthcontent.rI’lletransverse

    ;impactenergyvaluereachesamaximumasrareearth ;is0.03%.thenitdecreasesgradually.Thereasonis ;thattheadditionofrareearthchangesplasticband

    ;likemanganesesulfideinclusionsintosphericaloxy

    ;sulfidesulfoxideinclusionswithhighhardness.Thev ;arehardtobedeformedandcanhardlybeextended ;Table1Chemicalcompositionsoftestingsteels(%,massfraction)

    ;

    ;ZhuXyet.

    ;

    ;

    ;,

    ;RoleofRareEarthinLowSulphurNb-Ti-bearingSteel ;wR|/%./

    ;Fig?1EffectofrareearthcontentonyieldstrengthFig.2Effectofrareearthconcentontransversetensilest

~nsth

    ;/%

    ;Fig.3Effectofrareearthcontentonelongation ;/%

    ;ng.4Effectofmearthcorbel-itontransvqirseillenelgyat20?

    ;alongtherollingdirectionduringrolling.Thestress ;concentrationcanbegreatlyreleasedbythespherical ;inclusions,whichleadstothedifficultyoftranSVerse ;fractureandincreasestheimpactenergyvalues.But ;excessiverareearthmakestheimpactenergyvalues ;decrease.Whenexcessiverareearthisadded.cerium ;canbecombinedwithirontoformjntermetallicCO- ;mpounds.Theintermetalliccompoundsarehard. ;brittleandlargeinsize,andwithdifferentstructures ;fromthoseofmatrixmetal,SOtheyworsentheproper

    ;tiesofstee1.

    ;2.1.4Effectofrareearthontheanisotropyinlowsu1.. ;phurNbTibearingsteelTable3showstheanisot

    ;ropyofyieldstrength,tensilestrengthandimpacten

    ;ergyinlowsulphurNbTibeatingsteels.Itindicates

    ;thatproperamountofrareearthcanimprovethe ;anisotropyofimpactenergyabove20?.Thisis

    ;becausethatthesphericaloxysultldesulfoxideinclu. ;\I.|lllI

    ;,u01l&lIo

    ;

    ;JOURNALOFRAREEARTHS,Vo1.21,No.1,Feb.2003 ;Table3AnisotropyinlowsulphurNb-Ti-bearingsteel(transverse/longitudina1)

    ;sionsofrareearthcanreducetheanisotropyofinclu- ;sions.Butexcessiverareearthcanworsentheanisot

    ;ropyofimpactenergy.Rareearthcannotimprovethe ;anisotropyofimpactenergybelow20?andthe

    ;anisotropiesofyieldstrengthandtensilestrength. ;2.2Eofrareearthonmicrostruc-

    ;turesinlowsulphurNb?-Ti?-bearing

    ;steel

    ;Thechangesofmicrostructuresowingtotheaddi- ;tionofrareearthareshowedinTable4.Figs.5and6 ;showthemicrostructuresofsamplesNo.1and2re

    ;spectively.ItcanbeseenthatthemicrostructureiS ;stillcomposedofferritesandpearlitesinspiteofthe ;additionofrareeanh.However,themicrostructureiS ;refinedandtheamountofpearliteiSincreased.The ;increaseintheamountofpearliteiScausedbythefo1.

    ;1owingfactor.RareearthCanrefinetheaustenite ;grainsandincreasethetotalareasofgrainboundary, ;whichincreasesthenucleationsitesofpearliteand ;thusincreasestheamountofpearlite.

    ;2.3Eectofrareearthoninclusionsin

    ;lowsulphurNb-Ti-bearingsteel

    ;Fig.7and8showtheeffectofrareearthonin- ;Fig.5MierostruetureofsampleNo.1

    ;Table4Microstructuresandgrainsiz(~intestingsteel ;clusionsinlowsulphurNb-Ti.bearingstee1.ItCallbe ;seenthatboththeaveragelineardiametersandtheav

    ;erageareasofinclusionsdecreasewithincreasingthe ;contentofrareearth.Sodotheaveragemaximumdi

    ;ametersandminimumdiametersofinclusions.Onone ;hand.itshowsthatrareearthcleansthemoltensteel ;andreducestheamountofinclusions.Ontheother ;hand.rareearthmakestheinclusionsspheroidizd,re

    ;finedanddispersed,andthusimprovesthedistribut. ;ionsofinclusions.

    ;1.Withincreasingcontentofrareearth,the ;transverseyieldpointandtensilestrengthdeclineini

    ;tiallyandthenrise;SOdoestheelongation. ;2.Withincreasingcontentofrareearth,the ;transverseimpactenergyvaluesriseinitiallyandthen ;declineatvariOUStemperatures.Astherareearthcon. ;tentisabout0.03%.thetransverseimpactenergy ;valuereachesamaximumvalue.thenitdecreases ;gradually.

    ;3.Propercontentofrareearthcanimprovethe ;anisotropyofimpactenergyobviouslyabove20?.

    ;Rareearthdoesnotimprovetheanisotropyofimpacten

    ;ergy.yieldstrengthandtensilestrengthbelow20?.

    ;Fig.6MicrostructureofsampleNo.2

    ;

    ;ZhuXYeta1.RoleofRareEarthinLowSulphurNb?Ti-bearingSteel ;wp.

    ;~/%

    ;Fig.7EffectofI21reearthonlineardiameterofinclusions ;

    ;\

    ;

    ;0

    ;

    ;

;/%

    ;Fig.8Effectofrareearthonareaofinclusions ;4.Propercontentofrareearthcanrefinethe ;grainsandincreasetheamountofpearlite. ;5.Rareearthinfluencestheinclusions.Onone ;hand.rareearthcleansthemoltensteelandreduces ;theamountofinclusions;ontheotherhand,rareearth ;makestheinclusionsspheroidizd,refinedanddisper

    ;sed,andthusimprovesthedistilbutionsofinclusions. ;References:

    ;******’****

    ;EffectsofLightandHeavyRareEarthonAnti-Declining ;PropertyofNodularCastIron

    ;GuoErjun,WangLiping,YaoXiurong(MaterialsScienceandEngineeringCollege,HarbinUniver ;sityofScienceandTechnology,Harbin150080,China) ;Abstract:Theeffectsrareearthelementswithdiffer

    ;entcontentonantidecliningpropertyofYbaseheavy

    ;rareearthmagnesiumandceriumbaselightrareearth. ;magnesiumnodularcastironwerestudied.Therela

    ;tionshipsbetweenthesphericizedgradeoftheliquid ;irontreatedbydifierentnodulizerandholdingtimeal

    ;SOwereobtained.Theresultsshowthatthemorethe ;remainsoftherareearthare.the1ongertheanti.de. ;cliningtimeis,eithertheliquidirontreatedbyY.Mg. ;SiorbyCeMg.Sinodulizer.Whenthecontentsofthe ;remaindersrareearthareovercertainquantity,the ;Keywords:rareearths;nodularcastiron;antidecliningproperty;Ce ;primaryspheilcizedgradewi11declineenliquid

    ;irontreatedbyYMgSiorCeMgSinodulizercon

    ;tainstheproperremainsofrareearth(about0.04% ;

    ;0.06%),theantidecliningpropertyisthebest.

    ;Meanwhile,theMgremaindersisabout0.04%0.

    ;07%.Themiddleremainsrareearthoftherareearth

    ;MgnodulizerwithmiddtingremindersofREisbetter ;thantheMgSiinantidecliningproperty.ButYMg

    ;SinodulizerisbetterthantheCeMgSi.Sometimes

    ;Ce??Mg??Sinodulizercanbeusedfortheproductionof ;heavysectionnodularcastironwithlangesection ;baseligIltrafeearth;Ybaseheavyrareearth ;(SeeJ.Chin.RE.Soc.(inChin.),2003,21(1):44foffulltext) ;

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