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-Ti—bear—
;ingsteelwereinvestigated.Itisshownthatthetransverseyieldpoint,thetraversetensilestrengthandelongationoftest—
;ingsteelsdecreaseinitiallyandthenrisewithincreasingcontentofrareearth.Theimpactenergyvaluesofthetesting
;steelsexhibitacontrarytrend.Properamountofrareearthinthesteelscanimprovetheanisotropyofimpacttoughness
;above一20?
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:1002—0721(2003)01—0081—05
;The印plicationofrareearthinsteelisdevelop—
;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,sothemicro—alloyingeffectofrare
;earthinthesteelbecomesmoreandmoreimportant. ;Recently,manyinvestigationshavebeenmadeonthe ;roleofrareearthandmicro.alloyingelementssuchas ;niobium.vanadiumandtitaniumetc.insteels【9J.
;However.theinteractionsbetweenrareearthandmi—
;cro—alloyingelementshavenotbeeninvestigatedwhen ;niobiumandtitaniumareaddedsimultaneously,espe. ;ciallyinlowsulphurmoltenstee1.FormakingfuUuse ;ofChineseresourcestodevelopthemicroalloying ;steelswithrareearth,itisverynecessarytoinvesti. ;gatetheinteractionmechanismbetweenrareearthand ;niobiumandtitanium.,I1llispaperintendstoinvesti. ;gatetheinteractionofrareearthwithniobiumandtita. ;niuminlowsulphurNb—Ti—bearingstee1.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:200l一09一l7:reviseddate:2002—03—26
;Foundationitem:ProjectsupportedbytheNationalItemsof8.5P叫ect
;BiographyZhuxingyuan(1964一),Male,Doctor,Associateprofessor ;*CommOo~author(E—mail:zxyzxy@public.wh.hb.cn) ;
;beforetapping.A50kgingotwascastforeverytest—
;ingladle.’Thechemicalcompositionswereanalyzed
;bytwosamplestakenfromdifferentpositionsofthein—
;gottoensuretheaccuracy.Theanalysisresultsare ;showninTable1.
;1.2Analysismethodsoftestingsteels
;Themechanicalpropertiesoftestingsteelswere ;measuredbyWE一6Otensiletestingmachine.Thesize ;oftestingsamplesis8mm×40min×210mm.The ;impactpropertiesoftestingsteelsatthetemperature ;rangefrom20to一78oCweretestedbyJB一30Bim—
;pacttestingmachine,andthetestingsamples,witha ;sizeof5mln×10mln×55mm.werecharpyV—shape
;notched.ThemicrostructureswereobservedbyMM6 ;orOLYMPUS—PME3opticalmetallographicmicro—
;scope.Themetallographicsamplesweremechanically—
;preparedandtheetchantwasnita1.Quantitativemet—
;allographicanalysiswasconductedonIBAS--2000im-- ;ageandanalysissystemtodetermineandmeasurethe ;morphology,sizeandareaofinclusions,andthearea ;andsizeofpearlites.
;1.3Rollingoftestingsteels
;The50kgroundingotswerereheatedforabout ;twohsat1200oC.Two—stagecontrolledrollingwas
;carriedoutbyamini—rollingmil1.Theinitialrolling ;temperaturewasabout1150oC;therollingtempera—
;tureregionwithrecrystallizationwas1000—1150?.
;JoURNALOFRAgEEARTHS,Vol21,No.1,Feb.2003 ;2ResultsandAnalysis
;2.1EffectsofREonmechanicalproper-
;tiesoflowsulphurNb?-Ti?-bearing
;steel
;Effectsofrareearthonyieldstrengthandten—
;silestrengthoflowsulphurNb--Ti--bearingsteel ;Figs.1and2illustratetherelationshipbetweenrare ;earthcontentsandtransverseyieldstrengthaswellas ;tensilestrengthoflowsulphurNb—Ti—bearingstee1.It
;canbeseenthatboththetransverseyieldstrengthand ;tensilestrengthdecreaseinitially,andthenriseobvi—
;ouslywithincreasingcontentofrareearth.卟eeffects
;ofrareearthonstrengthhavetwosides.Ononehand, ;rareearthcleansthemoltensteel,whichhasaninter—
;actionwithnitrogenorphosphorusanddecreasesthe ;quantityofpearlite.Thisleadsthestrengthtoreduce. ;Ontheotherhand,rareearthissolidsolvedintothe ;steel,whichdecreasesthethicknessofpearlitelame1. ;1aes,andrefinesthegrainsandacceleratestheprecip—
;itationofcarbonitrides.Thisincreasesthestrength【….
;2.1.2Effectsofrareearthonelongationinlowsu1. ;phurNb—Ti—bearingsteelFig.3showstherelation—
;shipbetweenrareearthcontentandtheaveragetrans. ;verseelongationinlowsulphurNb—Ti—bearingstee1.It
;canbeseenthatthetransverseelongationdecreases ;initiallyandthenrises.
;2.1.3Effectsofrareearthonimpactenergyinlow ;andtherollingtemperatureregionwithoutrecrystalli--sulphurNb--Ti--bearingsteelTable2showsthea
v--
;zationwas800—950oC.Fortwostagecontrolledroll—
;ing,repetitivedeformationwasfirstappliedonthe ;testingsteelsintherecrystallizationtemperatureregion ;toproducefinerecrystallizationygrainswiththeaid ;ofmicro—alloyingelements,niobiumandtitaniumor ;theirprecipitates,whichprohibitsrecrystallizati ;Then,multi—passdeformationwasimposedonthefine ;grainedausteniteinthenon--recrystallizationtempera-- ;tureregionbeforetheaphasetransformation. ;Thus,alargeamountofnucleationsitesfor斗a
;phasetransformationwascreatedandfineferritegrains ;couldbeobtainedtoimprovethestrengthandductility ;oftestingsteelsl.’.
;eragetransverseimpactenergyvaluestorvanousrare ;earthcontentsatdifferenttemperatures.TheCOITe—
;spondingcurveoftransverseimpactenergyat一20?
;isshowninFig.4.Itcanbeseenthatthetransverse ;impactenergyValuesriseinitiallyandthendecrease ;withincreasingofrareearthcontent.rI’lletransverse
;impactenergyvaluereachesamaximumasrareearth ;is0.03%.thenitdecreasesgradually.Thereasonis ;thattheadditionofrareearthchangesplasticband—
;likemanganesesulfideinclusionsintosphericaloxy—
;sulfidesulfoxideinclusionswithhighhardness.Thev ;arehardtobedeformedandcanhardlybeextended ;Table1Chemicalcompositionsoftestingsteels(%,massfraction)
;
;ZhuXyet.
;山
;苫
;,
;RoleofRareEarthinLowSulphurNb-Ti-bearingSteel ;wR|/%./
;Fig?1EffectofrareearthcontentonyieldstrengthFig.2Effectofrareearthconcentontransversetensilest
~nsth
;/%
;Fig.3Effectofrareearthcontentonelongation ;/%
;ng.4Effectofmearthcorbel-itontransvqirseillenelgyat一20?
;alongtherollingdirectionduringrolling.Thestress ;concentrationcanbegreatlyreleasedbythespherical ;inclusions,whichleadstothedifficultyoftranSVerse ;fractureandincreasestheimpactenergyvalues.But ;excessiverareearthmakestheimpactenergyvalues ;decrease.Whenexcessiverareearthisadded.cerium ;canbecombinedwithirontoformjntermetallicCO- ;mpounds.Theintermetalliccompoundsarehard. ;brittleandlargeinsize,andwithdifferentstructures ;fromthoseofmatrixmetal,SOtheyworsentheproper—
;tiesofstee1.
;2.1.4Effectofrareearthontheanisotropyinlowsu1.. ;phurNb—Ti—bearingsteelTable3showstheanisot—
;ropyofyieldstrength,tensilestrengthandimpacten—
;ergyinlowsulphurNb—Ti—beatingsteels.Itindicates
;thatproperamountofrareearthcanimprovethe ;anisotropyofimpactenergyabove一20?.Thisis
;becausethatthesphericaloxysultldesulfoxideinclu. ;\量I.|lllI
;,u01l&lIo墨
;
;JOURNALOFRAREEARTHS,Vo1.21,No.1,Feb.2003 ;Table3AnisotropyinlowsulphurNb-Ti-bearingsteel(transverse/longitudina1)
;sionsofrareearthcanreducetheanisotropyofinclu- ;sions.Butexcessiverareearthcanworsentheanisot—
;ropyofimpactenergy.Rareearthcannotimprovethe ;anisotropyofimpactenergybelow一20?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.
;2.3E仃ectofrareearthoninclusionsin
;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 ;anisotropyofimpactenergyobviouslyabove一20?.
;Rareearthdoesnotimprovetheanisotropyofimpacten—
;ergy.yieldstrengthandtensilestrengthbelow一20?.
;Fig.6MicrostructureofsampleNo.2
;
;ZhuXYeta1.RoleofRareEarthinLowSulphurNb?Ti-bearingSteel ;wp.
;~/%
;Fig.7EffectofI21reearthonlineardiameterofinclusions ;量
;\
;一
;0
;‘磊
;三
;/%
;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—
;entcontentonanti—decliningpropertyofYbaseheavy
;rareearth—magnesiumandceriumbaselightrareearth. ;magnesiumnodularcastironwerestudied.Therela—
;tionshipsbetweenthesphericizedgradeoftheliquid ;irontreatedbydifierentnodulizerandholdingtimeal—
;SOwereobtained.Theresultsshowthatthemorethe ;remainsoftherareearthare.the1ongertheanti.de. ;cliningtimeis,eithertheliquidirontreatedbyY.Mg. ;SiorbyCe—Mg.Sinodulizer.Whenthecontentsofthe ;remaindersrareearthareovercertainquantity,the ;Keywords:rareearths;nodularcastiron;anti—decliningproperty;Ce ;primaryspheilcizedgradewi11decline鼢enliquid
;irontreatedbyY—Mg—SiorCe—Mg—Sinodulizercon—
;tainstheproperremainsofrareearth(about0.04% ;一
;0.06%),theanti—decliningpropertyisthebest.
;Meanwhile,theMgremaindersisabout0.04%一0.
;07%.Themiddleremainsrareearthoftherareearth—
;MgnodulizerwithmiddtingremindersofREisbetter ;thantheMg—Siinanti—decliningproperty.ButY—Mg—
;SinodulizerisbetterthantheCe—Mg—Si.Sometimes
;Ce??Mg??Sinodulizercanbeusedfortheproductionof ;heavysectionnodularcastironwithlangesection ;baseligIltrafeearth;Ybaseheavyrareearth ;(SeeJ.Chin.RE.Soc.(inChin.),2003,21(1):44foffulltext) ;一
;5—6.7
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