Tensile Properties and Microstructure of Weld Metal of X80 Steel by MAG Welding

Abstract

Tensile properties and microstructure of weld metal of X80 plates were evaluated. X80 plates were welded using full-automatic Gas Metal Arc Welding (GMAW) under several welding conditions. To clarify effects of welding conditions on weld joint performance in X80 pipeline, strength, toughness and hardness of weld joints were evaluated. Grain size and microstructural component of the weld metal were measured.
Overmatching for the specified minimum yield stress (SMYS) of X80 was obtained for all the welding conditions. If distribution of the yield stress of X80 base metal was taken into consideration, however, welding conditions to obtain overmatching were limited. The strength and hardness of the weld metal decreased as the heat input increased. This was due to the change of acicular ferrite lath width and percentage of grain boundary ferrite and ferrite side plate. On the other hand, Charpy impact energy was high, irrespective of the welding conditions.