Effect of Heat Input on Mechanical Properties and Microstructure of Gas Metal Arc and Shielded Metal Arc Girth Weld Metal of X80 Line Pipe

This study evaluated the weld joint performance of X80 line pipes welded using fully automatic Gas Metal Arc Welding and manual Shielded Metal Arc Welding in order to clarify welding conditions for yield stress overmatching with adequate fracture toughness and hardness taking into account the distribution of the yield stress of line pipes. In addition, we conducted metallurgical surveys of the weld metal to clarify factors dominating the yield stress of the weld metal. The results clarified that the welding conditions applicable to X80 line pipes were the heat input range of between 0.9 and 1.3 kJ/mm using solid wires classified as YGW24 and ER100S-G for GMAW and that of between 1.6 and 2.4 kJ/mm using electrode classified as E11016-G for SMAW. The metallurgical surveys revealed that the yield stress of the weld metal was dependent on the acicular ferrite lath width and percentage of the grain boundary ferrite, ferrite side plate and acicular ferrite. The heat input dependency of the yield stress of the weld metal could be explained from the viewpoint of the acicular ferrite lath width which was the main microstructure.