weldability+of+ultra-high+strength+pipeline+steel+x120

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1、IIWuhanUniversityofScienceandTechnologyAbstractX120ultrahighstrengthpipelinesteelwithhighstrengthandgoodlowtemperaturetoughnesswasobtainedbymeansofultralowcarbondesign，microalloyingandTMCPprocessing．Themicrostructureofthisstee“SdominantlyupperbainiticferriteTheadditionofmicroaIloyin

2、gelements(Nb，VTi，Zr)pinnedtheprioraustenitegrainboundaryandledtosmallaustenitegrains．TMCPprocessingresultedinpan-·cakeshapeaustenitegrainsandfinallyfine-·grainedmicrostructureinthebasemetalsteelplate．Themicrostructuralevolutionincoarse—grainedregionofheat．affectedzone(CGHAZ)ofX120ul

3、trahighstrengthpipelinesteelwasinvestigatedbymeansofthermalsimulationonaGleeble3500．TheCOntinuouscoolingtransformationcHrvesofsimulatedHAZrSH—CCT)wereobtainedsimultaneously．Asthecoolingraterangedfrom0．1。C／sto60。C／s．thepredominantlybainiticmicrostructurewasobtainedinthesimulatedCGHAZ

4、．BainitewasobtainedinthesimulatedCGHAZwhentheheatinDutofweldingwas12～25kJ／cm．TheVickershardnessofCGHAZwasbetween291-303HV10．Theimpacttoughnessatroomtemperaturewashighandstable(208～225J、．ThesimulatedresultsrevealedthatX120steelCanbeweldedinawiderangeofweldingheatinput．Afastcoolingpro

5、cesswasintroducedtoimprovethetoughnessoftheCGHAZ．TheweldingthermalcyclewasvariedinwhichboththeholdingtimeathightemperatureaboveAc3(瑚andcoolingtimefrom800to500。C(ts／5)wereshorten．Shorten臼ledtothinHAZwidthandfineprioraustenitegraininfusionline(FL)andCGHAZ：whiletheshortents／5resultedin

6、thethinnerbainite1ath．Themartenist．austinitefM．A)constituentsinfusionlinewerereducedandtheirmorphologywaschangedintothinfilm-like．AllthesefactorsplayedabeneficialroleinimprovingtoughnessofHAZofpipelinesteelX120．AccordingtotheSH．CCLtheheatinDutof21kJ／cmwaschosentoweldtheX120baseplate

7、utilizingthree-wiresubmergedarcweldingandtheabove．mentionedfastcoolingtechnique．Themicrostructureintheheat．affectedzonewasinvestigatedbymeansofopticalmicroscopyandscanningelectronmicroscopy．Thehardnessofheat．affectedzonewasmeasuredbyVickershardnessindenter．ResultsshowthattheX120line

8、pipeweldingjointhad