Microstructure and properties of MAG and oscillating laser arc hybrid welded X80 steel

Metal active gas welding (MAG) and oscillating laser arc hybrid welding (OLAHW) of X80 pipeline steel were carried out with backing weld by laser, the joint formation, microstructure and mechanical properties (microhardness, tensile properties and impact toughness) were studied. The results showed that sound joints without defects of pores, slag inclusion and crack were obtained by both the two processes. The joint microstructure was mainly composed of acicular ferrite (AF) and M-A components. Because of lower heat input, faster cooling rate and more nucleation sites promoted by the oscillated laser, more acicular ferrite and finer M-A components were formed within the OLAHW filled joints than those within MAG filled joints. The average microhardness and tensile strength of the joints obtained by the two filling processes were almost the same, but the hardness variation of OLAHW joints is gentler with less fluctuation. The impact energy of heat affected zone and weld zone of OLAHW filled joints were 277 and 217 J respectively, which is 64% and 42% higher than those of MAG filled joints.