Microstructure And Mechanical Properties Of X80 Pipeline Steel Welded Joints Obtained By Different Welding Processes

In the gas transmission pipeline project of west to east and the China-Burma and China-Russia, gas pipeline are planning to build a gas pipeline and its tendency of pipeline steels with high strength steel grades, namely of X80 pipeline steel, and X80 steel in the welding process, welding materials and welding detection research directly restricts the gas pipeline laying quality, especially in the transmission and gas pipeline welding is a very important part of pipeline construction. In this paper, X80 pipeline steel as the research object, analysis of the X80 steel chemical composition, mechanical properties and weldability, tested various welding technology of X80 steel, and the microstructure and properties of joint test analysis.When using the SMAW(the first process), the welding microstructure of X80 steel is mainly intragranular ferrite nucleation, small inclusions distribution in ferrite matrix. When using solid wire gas shielded arc welding with full automatic welding(the second process), the X80 steel welding joint in banded ferrite and bainite banded alternating distribution organization. When using metal powder cored wire gas shielded arc welding with full automatic welding process, the root of weld(the third process), microstructure, crystal shape iron core ferrite than filling the nucleation of ferrite coarse shape of weld, microstructure, crystal and many of the precipitates. Therefore, precipitation strengthening is root of weld hardness greater than filling welding. Quasi polygonal ferrite and M-A islands are distributed in ferrite grain and grain boundaries in the weld, when the metal cored wire is used for gas shielded welding(the fourth process).During the tensile strength of the welded joint, the tensile strength of the welded joint is significantly higher than that of the process one and process three, which is two and four, which can reach 722-745 MPa. When the hammer breaking test of the welded joint, the groove depth of the joint of the four welding process is about 3 mm. There was no crack in the welding process of four welded joints when the side bending test was carried out. The impact toughness of welded joint, welding process of arc welding HAZ toughness is the highest, and the whole welding process SSFCE four semi-automatic welding weld toughness is the highest. Welding joint of hardness test, welding process both cover surface layer or root welding layer hardness is the biggest, the cover surface layer hardness can reach 283.02 HV, process the cover surface layer hardness to high and root welding layer, the process of cover layer hardness than the root welding layer.Using metal powder cored wire for gas protection sealing welding and flux cored self protective padding, cover welding process of X80 pipeline steel welding the comprehensive mechanical properties are the best and the organization to quasi polygonal ferrite ferrite and distribution in the ferrite crystal grain boundary and M-A mainly. This paper presents the welding process of X80 steel overall scheme of the system, and provides support for the preparation of perfect welding process of X80 steel.