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X()()X60X65X70()(CGHAZ),Ti-V-Nb,TiX60X70TiX65,X60X70,,,,:(CGHAZ)080,,,,,(CGHAZ),Ti-V-Nb,,,,,,,,,,,,,[13],,,,,X60X65X70,,1X60NUCORX65X70X60X65X707mm8.7mm12.7mm,1X,940032199912HANJIEXUEBAODecember19991(%)Table1Chemicalcompositionsofsteelsused(%)SteelCMnSiPSNbVTiMoCuNX600.091.180.230.0060.0010.0200.0100.0240.2410.1810.0073X650.071.280.280.0150.0070.0410.0440.0080.0090.0880.005X700.141.350.250.030.0090.040.0650.028//0.0059,1.94.8[4],,,,0.3MPa0.6MPa30m60m;(20mm)()T203A20kJ/cm,12kJ/cmHVA10AGB265089,5mm10mm55mm(X60X65),10mm10mm55mm(X70),V,L[5]22.1123X60X65X7013,;,;;,,,,,2.2,100L,G=-3.24-6.64logLG[5],22L/mTable2MeangrainsizeLofthebasemetalandtheCGHAZofvariousweldsonsteelsusedSteelBaseMetal0.15mWetWelding30mWetWelding60mWetWeldingHighEnergyWetWeldingWarm-keepingWetWeldingLocallyDryWeldingIn-airWeldingLGLGLGLGLGLGLGLGX606.411.3364.534.66////65.284.63//73.64.2883.23.93X6528.86.9984.203.9082.403.9682.863.98101.83.3590.883.68102.43.33121.62.84X7013.39.2376.804.1676.164.1978.084.1180.004.0478.934.0894.083.58113.23.0437(a)X60basemetal(b)0.15mwetwelding(c)Locallydrywelding(d)In-airwelding1X60200Fig.1MicrostructuresofX60steelbasemetalandCGHAZofvariouswelds200(a)X65basemetal(b)0.15mwetwelding(c)Locallydrywelding(d)In-airwelding2X65200Fig.2MicrostructuresofX65steelbasemetalandCGHAZofvariouswelds20038(a)X70basemetal(b)0.15mwetwelding(c)Localdrywelding(d)In-airwelding3X70200Fig.3MicrostructuresofX70steelbasemetalandCGHAZofvariouswelds2002.3HV3,98N7,3HV(98N)Table3MaximumhardnessHVofthebasemetalandtheCGHAZofvariousweldsonsteelsused(98N)SteelBasemetal0.15mwetwelding30mwetwelding60mwetweldingHighenergywetweldingWarm-keepingwetweldingLocaleryweldingIn-airweldingX60196325//297/284210X65205342339346319325266216X702103453423453093223042472.4GB265089,-15V433.1,,,39,,4Akv(-15)Fig.4BasemetalandCGHAZCharpy-Vlongitudinalabsorbedenergyofvariousweldsonsteelsused(-15)3.2Ti-V-Nb,[6],,Zener[7]:D=23dfD;d;f,,,,,,[8],X60X65X70:TiV;Ti,,VTi,V,TiVNb,(1000)Ti,;V,Ti,X60X70Ti(1),Ti[8];X65Ti/V,V[8],,,X60X70(2),(4)4,,X60X70X65,X60X70Ti,Ti0.024%0.028%,X65(1)X6087%Ti,,12kJ/cm,TiN1nm[8],Ti,,X70,V,Ti,Ti,X65(2)X65Ti,V,,V,2:,X6040L64.53m,X6584.20m,,V,VNbCN,,M3,,X65X603.3,,;,,,,t8/52s,500125/s[9],M,B;,M(13),3,,M,X60X70,M,,,M,,M,;,TiN[10][11],,,,,:X65,(2)3.4,,,M,;,,,,,,X60TiN,,TiN[8],(2),B,X65V[8],,,V,,;,,VNbCN,,,,,(3),,,X70Ti,[4]:X60820kJ/cm,,30kJ/cm,X60,,30kJ/cm3.541[8],4,,,,,,Ms,,4,41J,27J[4]4(1)CGHAZX60X70CGHAZX65,TiCGHAZ(2);;(3)X60X70,;,(4),0.15m12kJ/cm20kJ/cm,X60X70CGHAZ13%21%,X6526%(5),,(1998-04-08,1999-11-12)1WangGR,NorthTHandLeewisKG.MicroalloyingAdditionsandHAZFractureToughnessinHSLASteels.WeldingJour2nal,1990,1:142s222s.2PalmiereEJ,GarciaCIandDeardoAJ.TheInfluenceofNiobiumSupersaturationinAusteniteontheStaticRecrystalliza2tionBehaviorofLowCarbonMicroalloyedSteels.MetallurgicalandMaterialsTransactionsA,1996,27A(4):951960.3RakI,GlihaVandKocakM.WeldabilityandToughnessAssessmentofTi-MicroalloyedOffshoreSteel.MetallurgicalandMaterialsTransactionsA,1997,28A(1):199206.4,,.X60.,1992,15(6):2430.5..:,1987.109111.6..:,1991.376.7EasterlingKE.IntroductiontothephysicalMetallurgyofwelding.London:Butterworths,1983.104155.8,.CGHAZ.,1999,27(9):2531.9.:[].:,1987.10PenttiKarjalainen,.(TMCP+Acc).,1995,18(5):33.11..,1987,23(3):A223.12VogtGHetal.Toughnessrequirementsarestudiedforlarge-diametergaspipeline.OilandGasJournal,1984,8:105108.42Coarse-GrainedHeat-AffectedZone(CGHAZ)ToughnessofUnderwaterWeldsonMicroalloyedHighStrengthSteelsShiYonghua,WangGuorong(SouthChinaUniversityofTechnology)LiGenquan,JinShilin(BaojiPetroleumSteelPipeandTubeWorks)AbstractThemicrostructure,grainsize,hardnessandCharpy-Vimpacttoughnessoftheunderwaterandin-airweldingforcoarse-grainedheat-affectedzone(CGHAZ)ofthreeTi-V-Nbmicroalloyedsteels,gradeX60X65andX70respectively,wasinvestigated.Thebasemetalofthethreesteelswasalsoexamined.TheeffectsofprecipitatesbehaviorinthermalcycleandheatinputonCGHAZtoughnesswerediscussed.Itwasfoundthat,thedissolutionofTi-V-Nbprecipitatesinmicroalloyedsteelsduringtheweldthermalcy2clesledtothecoarseningoftheCGHAZgrainandthereforethedeteriorationoftoughness.TheCGHAZtough2nessofX60andX70steels,whichcontainhigherTi,isbetterthanthatofX65steel.ForX60andX70steelsinthisresearch,theCGHAZtoughnessofunderwaterweldingisworsethanthatofin-airwelding.Inaddi2tion,theCGHAZtoughnessoflocallydryunderwaterweldingishigherthanthatofwetwelding.Low-carbonmartensitepresentedintheCGHAZofunderwaterweldsduetothegreatquenchingeffectofthewateraroundtheweldzone.Increasingtheheatinputinunderwaterwetweldingoradoptingwarm-keepingmethodcouldincreasetheCGHAZtoughness.Whilethewaterdepthincreased,theCGHAZtoughnessofsteelsusedde2creased.Keywordsmicroalloying,coarse-grainedheat-affectedzone(CGHAZ),underwaterwelding,toughness,,197312,1998:43