Research,Development,and
;(1.CentralIronandSteelResearchInstitute,Beijing100081,China;2.CapitalIronand
;SteelGroupCompany,Beijing100041,China) ;Abstract:Theresearch,production,andapplicationofV—NmicroalloyedhighstrengthrebarsinChinawerere—
;viewed.Enhancednitrogeninvanadium-containingrebarspromotestheprecipitationoffi
neV(C,N)particles,and
;markedlyimprovestheprecipitationstrengtheningeffectivenessofvanadium.
;Therefore,vanadiumaddedtoV—Nmi—
;croalloyedrebarscanbereducedby40%ocomparedtothesamestrengthlevelofvanadium-
containingrebars.
;Keywords:highstrengthreinforcedbar;V—Nmicroalloying;precipitationstrengthening
;Reinforcingbars,38thebiggeststeelproducts ;inChina,accountforaboutone—fourthofthetotal
;steelproduction.Inrecentyears.theproduction ;andconsumptionofhot—rolledrebarsinChinahas
;increaseddramatically,withfastdevelopmentofthe ;nationalbuildingindustry.AsshowninFig.1.the ;totalannualrebarproductionin2004approaches71rail—
;liontons,nearlyfivetimesasmuch38thatin1995. ;However,therebarproductmixhasnoobvious ;change3syet,andisstilldominatedbygrade2re—
;barsinChinabuildingmarket.Atpresent,near ;8Ooftherebarproductionisgrade2rebars.with ;minimumyieldstrengthof335MPa,intheChinese ;market.However,inthedevelopedcountries.the ;rebarsforbuildinghavebeenupgradedtograde3re—
;bars,withanyieldstrengthof400MPaorabove. ;Forexample,grade4rebarswithyieldstrengthof ;500MPahavebeenwidelyusedinGermany[.A
;largenumberofapplicationexperiencesindicatethat ;rebarconsumptioncanbesavedbv14ifthe
;strengthoftherebarsareupgradedfromgrade2to ;grade3.Therefore,therewillbe3greatsocialand ;economicbenefitsifsubstitutionofgrade3reb3rs ;forgrade2rebarsispromotedinChina.
;Inthepresentstudy,theresearch,production, ;andapplicationofhigh——strengthrebarstotheV—N
;microalloyedprocessinChinawerereviewed. ;Fig.1ProductionofrebarsinChinainpastdecade ;1ExperimentalResearchofV—NMicroalloyed
;HighStrengthRebars
;Themicroalloyingprocessismainlyadopted ;todevelophigh？strengthweldablerebars,allover ;theworld[.Duringrebarproduction.3high ;rollingspeedandhighfinishrollingtemperatureare ;quitesuitablefortheapplicationofthevanadiummi—
;croalloyingtechniqueinrebaralloydesign[.The ;latestrebarstandardissuedinChinaalsorecom—
;mendstheuseofvanadiummicroalloyingtoproduce ;grade3rebarswiththeminimumyieldstrengthof ;400MPaL.However,vanadiumadditionwill ;markedlyraisetheproductioncostofrebars.Itis ;knownthatthemicroalloyingelementtakeseffectby ;Biography:YANGCai—fu(1965
一),Male,Doctor,Profess0r;E-mailyangcaifu@cisri.com.c”;RevisedDate:Ap剐
28,2006
;苫,f-I00_J罩0.I岛—盛0-IJ
;
;?
;82?JournalofIronandSteelResearch,Internationa1V01.15 ;precipitationofitscarbonides/nitrides.andmicroal—
;loyednitrideshavenoticeablybetterstrengthening ;effectivenessthancarbonides,asthenitrideparticles ;arefinerandmorestable.Anumberofresearchre—
;suits引indicatethatnitrogenisacost—effectiveal-
;loyingelementinvanadiummicroalloyedsteels,and ;thestrengtheningeffectivenessofnitrogeninvana—
;diumbearingsteelcanreachastrengthincrementup ;toabout6MPaper0.0010ofnitrogen.TheSUC—
;cessfulapplicationofV—Nmicroalloyedtechnology
;tohigh—strengthrebarshelpstodevelopacost—-ef—-
;fectivemethodforgrade3rebarproductioninChi—
;na[6—91
;.
;1.1Effectofnitrogen
;Fig.2showstheeffectofnitrogenonthe ;strengthofvanadium—bearingrebarstee1.Withthe
;samevanadiumcontent,thestrengthofV—Nsteelis
;muchhigherthanthatofvanadiumstee1.Itcanbe ;seenthatwiththeenhancementof0.0100inni—
;trogen,theyieldstrengthandtensilestrengthofV—
;Nsteelincreaseby117.5MPaand135MPa.re—
;spectively,comparedtovanadiumstee1.Theresults ;showthatnitrogenmarkedlyimprovesthestrength—
;eningeffectivenessofvanadiuminsteel.which ;meansthatnitrogenisaveryeffectivestrengthening ;elementforvanadium—bearingrebars.
;1.2Vanadiumdistributionandprecipitationinrebars ;Vanadiumdistributioninvanadium—containing
;steelandV—NsteelisshowninFig.3.Invanadium- ;containingsteel,vanadiummainlyexistsassolidso—
;lutionaccountingfor56.3ofthetotalvanadium ;content,whereas,only35.5ofvanadiumprecipi- ;tatesintheformofV(C.N).Theresultsreveal ;thatmostofthemicroalloyingelementinvanadium- ;containingsteeldoesnotworktowardprecipitation ;『00
;垂芎5o0
;皇
;?
;400
;0.11V一0.0085%N
;steel
;0.12%V一0.018%N
;steel
;Fig.2Thestrengthofvanadium-containingsteeland,Nsteel ;100
;皿Vv(c,N)
;目VMaC
;口Vsoluble
;V—-containingsteelV—-Nsteel
;Fig.3Vanadiumdistributioninvanadium-containing ;steelandV-Nsteel
;strengtheninganditisawasteofvanadiulT1.Onthecon- ;trary,inV-Nsteel,70ofvanadiumforrnsV(C,N)pre—
;cipitatesandonly20dissolvesinthematrix. ;Hence,nitrogenadditionaltersvanadiumdistribu—
;tioninsteel.andpromotestheprecipitationofvana—
;diumdissolvedinthematrix.thusimprovingthe ;precipitationstrengtheningofvanadium. ;Table1liststheresultsofV(C,N)precipitate ;volumesinvanadium—containingsteelandV—Nstee1.
;ItcanbeseenthattheamountofV(C,N)precipi—
;tareinV—Nsteelisovertwiceasmuchasthatnva—
;nadium—containingstee1.Itisclearthattheenhanced
;nitrogeninV—Nsteelpromotesvanadiumprecipitation ;markedlyanditshouldbeoneofthemainreasonsfor ;thestrengthimprovementinV—Nstee1.
;Fig.4showsthesizedistributionofV(C,N) ;precipitates.Thefractionoffineparticleswithasize ;oflessthan10nminvanadium—containingsteels
;iust21.1,whereas,thefractionisupto32.2in ;V—Nstee1.Astheresultshows.nitrogenadditionin ;steelnotonlypromotesprecipitationofV(C,N), ;butreducestheaveragesizeofV(C,N)particles, ;andgreatlyincreasesthefractionoffineparticlepre—
;cipitates,whichalsomakesagreatcontributionto—
;wardincreasingthestrengthinV—Nstee1.
;Table1MasspercentofV(C.N)precipitatesin ;vanadium-containingsteeland,Nsteel
;???加0
;八王r号高—rB芎0写唇nq葛卫口
;
;Issue2Research,Development,andProductionofV—NMicroalloyedHighStrengthRebars?83?
;Particlesize/nm
;Fig.4ParticlesizedistributionofV(C,N)precipitatesin ;vanadium-containingsteel(a)andV-Nsteel(b) ;1.3StrengtheningmechanismofV.Nrebars ;Onthebasisofnumerousresearchresults,the ;strengthofmicroalloyedsteelsRcanbeexpressed ;by[:
;R一85.74-37wM4-83ws4-17.4×D一.+RPR(1)
;whereWM,叫sarethecontentofmanganeseandsil—
;icon,respectively;thesecondandthethirdterms ;denotemanganeseandsiliconsolidstrengthening, ;respectively;theforthtermdenotesgrainrefine—
;mentstrengthening;andRPRdenotesprecipitation ;strengthening.
;Accordingtotheexperimentalresultsofferrite ;grainsizeandyieldstrengthfortestedsteels,the ;contributionofeachstrengtheningmechanismtothe ;yieldstrengthofvanadium—rcontainingsteelandV—rN
;steelisshowninFig.5.Itcanbeseenthatthe ;strengthdifferencebetweenvanadium-containingsteel ;2OMlnsjv--containingV--Nrebar
;rebar
;Fig.5Strengtheningmechanismof20MnSi,vanadium- ;containingrebar,andV-Nrebarsteel
;andV—Nsteelmainlyresultsfromdifferentcontri ;butionsofprecipitationstrengtheningandgrainre ;finementstrengthening.Thecontributionofprecipi ;tationstrengtheningandgrainrefinementstrengthe ;ningontheyieldstrengthforV_Nsteelisover70%. ;2ProductionandPropertiesofV__NMicroal_. ;loyedRebars
;2.1Optimizationofchemicalco~itionforV-Nrebars ;Onthebasisofresearchstudiesinthelaborato—
;ry,thestrengtheningcapabilityofvanadiumandV—
;Nmicroalloyinginhighstrengthrebars,produced ;bytheconverterandcontinuouscastingprocess, ;havebeencompared,usingmillscaletrials.The ;railltrialresultsareshowninFig.6.Itcanbeseen ;thattheV-Nrebarscontainingvanadiumof0.03一
;0.09andvanadium—containingrebarswithvanadi—
;umof0.06？0.14reachalmostthesame
;strengthleve1.Themilltrialresultsalsoindicate ;thatthestrengtheningcapabilityofvanadiuminV—N
;steelismuchstrongerthanthatinvanadium？contai—
;ningstee1.Thus,foragivenstrengthrequirement, ;thevanadiumcontentinV—Nmicroalloyedsteelcan
;bemarkedlysavedwhencomparedwithvanadium—
;containingstee1.
;Theregressionresultsonthestrengthdataof ;themilltrialrebarsindicatethattheyieldstrengths ;ofvanadium—containingsteelandV—Nsteelcanbe
;expressedasperthefollowingformulae: ;Vanadium—containingsteel
;R一R(20Ms.)4-1056×叫v(2)
;V—Nsteel
;R一尺(20Msi)4-1994×7.ov(3)
;where7.ovisthemasspercentofvanadium. ;Itcanbeseenclearlyfromtheregressionre—
;suitsthatthestrengtheningeffectofvanadiuminthe ;V—Nrebarsisalmostdoublewhencomparedwith ;thatofthevanadium—containingrebars.
;VanaeliUlTIeonten%
;Fig.6Effectofvanadiumonthestrengthforthe ;milltrialscalerebars
;逞u口
;Bd?
;Bd?当?pl,d
;
;JournalofIronandSteelResearch.InternationalVoI.15 ;Theoptimizedcompositionsofgrade3rebarswith ;vanadium.containingandV_-Nmicroalloyedprocess ;aregiveninTable2.ThevanadiumcontentinV—N
;microalloyedgrade3rebarswithminimumyield ;strengthof400MPacanbereducedto0.02一
;0.04,andisonlyhalflevelinV-Femicroalloyed ;grade3rebars.
;2.2ProcesscOnsideratiOn
;Iti8easytocontroltheproductionprocessfor ;V-Nmicroalloyedgrade3rebars.Asamatteroffact, ;therei8essentiallynodifferenceintheproduction ;processofV—Nmicroalloyedgrade3rebarscom-
;paredtothatof20MnSgrade2rebars.Forachie- ;vlngthemaximumpreclpltatlOnstrengthenlng ;effect.iti8necessarytomakesurethattherei8full ;dissolutionofvanadiumcarbonitridesduringsoa—
;king.ItisnotdifficulttodissolveV(C,N)precipi—
;tatesfullyinvanadium—containingsteelbecauseof
;itshighsolubility,hence,thebillet8reheatingtem—
;peratureisnottoohigh,andnormallyitisreheated ;to1150—1200?.Theacceleratingcoolingprocess ;isgenerallyusedafterfinishrolling,forrefiningthe ;finalferritegrainsize.
;Steadyrecoveryofvanadiumandnitrogenis ;vcryimportanttocontrolthefluctuationofthere—
;bar8properties.Thestatisticalresultsfromanumber ;ofindustrialproductiondatashowsthatthescatterof ;thevanadiumcontenti8verynarrow(4-0.002)inV- ;Ngrade3rebarsmicroalloyedbytheNitrovanalloy,an ;additiveofvanadiumandnitrogen.Incontrast,thescat—
;terinthevanadium-containingrebarsteeladdingfer—
;rovanadiumreachesthelevelof-+-0.01andi8almost ;5timeshigherthanthatinV-Nrebars.
;NitrogencontentinV—Nsteelsdependsonthe
;vanadiumaddition.Therailltrialresultsshowthat ;foroptimizedindustrialoperations,wheneach ;0.01ofvanadiumi8added,0.O010ofnitrogen ;isaddedforNitrovan12andabout0.0013ofni- ;trogeni8addedforNitrovan16.
;2.3PropertiesofV—Nrebars
;2.3.jTensileproperties
;ThemechanicalpropertiesofV—Nmicroalloyed
;grade3rebarsaregiveninTable3andTable4,and
;theeffectoftherebarsizeonthemeehanicalproper—
;tiesi8showninFig.7.Itcanbeclearlyseenthatthe
;mechanicalpropertiesofV—Nmicroalloyedrebars ;arequitestable.Theyieldstrengthfluctuatesbe—
;tween425MPaand500MPawithafluctuation ;scopeof75MPa,althoughthetensilestrengthfluc—
;tuatesbetween575MPaand660MPa,withafluc—
;tuationscopeof85MPa,andelongationi8between
class ;19and32.Allkindsofrebarsmeetone—
;anti—quakerequirements,wherethetensile/yield
;strengthratioi8higherthan1.25. ;Table2Thechemicalcompositionofgrade3rebarsinmasspercent
;N0te:1)ThenumberafterRes.isenhancednitrogenfromv_Nalloyadditive.
;Table3MechanicalpropertiesofV?Nmicroalloyedhot-rolledrebars
;460
;450
;430
;465
;445
;450
;425
;455
;440
;445
;490
;500
;485
;490
;485
;500
;475
;480
;500
;465
;478
;482
;463
;478
;468
;474
;447
;467
;458
;455
;600 ;59O ;585 ;605 ;590 ;590 ;575 ;605 ;595 ;59O ;640 ;640 ;62O ;640 ;645 ;660 ;640 ;625 ;610 ;625 ;631 ;625 ;616 ;622 ;62l ;623 ;608 ;6l4 ;602 ;608 ;29 ;26 ;26 ;22 ;24 ;l9 ;22 ;2O ;22 ;l8 ;32 ;33 ;29 ;29
;27
;3l
;29
;23
;24
;25
;3O
;28
;27
;26
;25
;26
;25
;22
;23
;22
;1.32 ;1.30 ;1.33 ;1.3O ;1.33 ;1.3l ;1.36 ;l_3l ;1.31 ;1.34 ;M加毖? ;
;Issue2Research,Development,andProductionofV—NMicroalloyedHighStrengthReb
ars?85?
;700 ;600 ;忘500 ;r./3 ;400 ;35
;逞
;曼25 ;0
;凹
;15
;Table4MechanicalpropertiesofV.Nmieroalloyedcoilingrebars
;10203040
;Diameterofrebars/mm
;Fig.7Effectofrebarsizeonthestrengthand ;theelongationofV.Nrebars
;2.3.2Strainaging
;Thestrain-agingindex.thatis,theincreasein ;flowstressafteraginginaprestrainedsample,was
Nrebars.By ;usedtoevaluatethestrainagingofV—
;therequirementofthenationalstandardonthe ;strainagingtest,theprestrainwasselectedas5, ;andtheagingas250?for1h.
;Table5showstheresultsofthestrainagingevalu- ;ationofV—Nrebarsand20MnSirebars.Theresults ;showthatnostrainagingphenomenonoccursinV—N
;rebars,butasignificantstrainagingresponsecanbe ;seennthe20MnSgrade2rebars.
;2.3.3Weldability
;Fourtypicalweldingmethodsforrebarjoints,in_ ;cludingflashbuttwelding(FBW),gas-pressurewelding ;(GPW).shieldmetalarcwelding(SMA),anddec—
;troslagpressurewelding(ESPW),havebeenusedto ;evaluatetheweldabilityofV—Nmicroalloyedrebars.
;ThetestingresultsinTable6showthatV—Nmicro—
;alloyedhot——rolledribbedrebarshaveexcellentweld——
;abilityandaresuitableforthedifferentwelding ;processesmentionedearlier.
;2.3.4Low-cyclefatigue
;Fig.8showsthecurveofthefatiguelifeofV—N
;and20SiMnrebars.Theexperimentalresultsindi—
;catethatthefatiguepropertyofV—Nrebarsisalittle
;betterthanthatof20SiMnrebars.
;Table5Eff~tofagingonthepropertiesofV.Nrebars ;Table6Themechanicalpropertiesofweldingjoints ;Note:discurvatureforcoldbending;andaisdiameterofsample.
;
;Journa1ofIronandStee1Research.1ntemationa1Vo1.15 ;当
;盖
;虿
;300
;250
;200
;150
;100
;4567
;Strain/%