Microstructure and mechanical properties of weld joints in laser-MAG hybrid welding of 390 MPa grade marine high-strength steel

Laser-MAG hybrid welding was carried out in 390 MPa grade marine high-strength steel. Cross-sectional morphologies and microstructures of the weld joints were investigated by stereo microscope and optical microscope, and the hardness and mechanical properties of the welds were analyzed in this study. The results indicate that the weld metal microstructures mainly consist of pre-eutectoid ferrite, side-plate ferrite, acicular ferrite and lath bainite at the welding speed of 0.8 m/min. As the welding speed is 1.2 m/min, the amount of pre-eutectoid ferrite and side-plate ferrite decreases, whereas that of the acicular ferrite and lath bainite increases. The hardness of the weld joints is higher than those of the base metal, showing no obvious soften zone. Laser-MAG hybrid welds exhibits sound low-temperature impact toughness, and the impact absorbed energy of the weld metal at −40 ℃ and −60 ℃ increases with an increase in the welding speed.