Study On Microstructure And Properties Of Submerged Arc Welded Joint Of X80Pipeline Steel After Quenching And Tempering

In pipeline construction, hot bending bends and fittings is an important part ofconnection pipeline. For X80pipeline steel longitudinal seam submerged arc weldedjoint technology is mainly used in quenching and tempering of X80hot bended pipeand pipe fittings. In the hot bending pipe and pipe fittings quenching and temperingprocess, including the base metal, heat affected zone and the weld, welding joint is anindivisible whole, therefore, the welding joint of X80pipeline steel after quenchingand tempering treatment after the change trend of organization of the submerged arcwelding, and then make the welding and heat treatment process fit, have veryimportant significance to improve the overall performance of X80grade steel pipesand hot bending bend.In this paper, by studying the changes of X80pipeline steel submerged arclongitudinal weld tempering and performance organization, the effect of X80pipelinesteel major joint performance of welding. Through theoretical analysis, further perfectorganization to improve the performance of welded joints of X80pipeline steel wereput forward from the grain size, phase composition, carbon nitride precipitation inthree aspects, and the welding and heat treatment of alloy design, from the threeaspects of the next process optimization direction and way of thinking, to providetheoretical support for the welding and heat treatment of X80pipeline steel.According to the theoretical analysis, proposed the ideal welding joint ofaustenite grain size of X80pipeline steel should be controlled below10μm afterquenching and tempering treatment, bainite lath size should be controlled in1~2μm,ideal precipitate size should be controlled below80nm, and try to avoid carbon nitrideprecipitation size larger than1μm. The ideal microstructure of X80pipeline steelshould be strengthened and ductile phase hybrid structure, the proportion of ductilephase should be controlled at10~20%, the ideal organization tempering weld seamof X80pipeline steel after should be lath bainite, lath martensite as reinforced phase,the MA organization and a certain amount of iron ferrite as ductile phase, MA shouldbe fine, uniform and dispersed. Weld heat affected zone of X80pipeline steel in thepursuit of the goals of the organization are lath bainite or martensite as reinforcedphase, MA and iron with a certain amount of ferrite organization as ductile phas。 In order to obtain the above characteristics, the existing system in alloy design,can consider to increase the content of nickel in the weld metal, in order to improvethe low-temperature impact toughness of weld metal. In the welding process, can beconsidered to reduce the welding heat input, and appropriately increasing thepreheating temperature, but the preheating temperature should not exceed200℃.In the process of heat treatment process optimization, may consider appropriateto reduce the quenching temperature. Appropriate prolonging quenching holding time.Finally, the appropriate increase the concentration of sodium chloride in water, inorder to improve the quenching cooling rate.