Microstructure and mechanical properties of weld metal in laser and gas metal arc hybrid welding of 440-MPa-grade high-strength steel

Fiber laser and gas metal arc hybrid welding of 440-MPa-grade high-strength marine steel was carried out at different welding speeds. The influence of welding speed on the microstructure and mechanical properties of weld metal was investigated. The weld-metal microstructure mainly consisted of pre-eutectoid ferrite, side-plate ferrite, acicular ferrite and lath bainite at a low welding speed. With the increase in welding speed, acicular ferrite and lath bainite were the dominant weld-metal microstructures. All samples failed at the base metal during tensile tests, which indicates that there is no soft zone in the hybrid welds. The welding speed had a significant effect on the impact toughness of the weld metal. The impact absorbed energy of the weld metal increased from 35 to 105 J with the increase in welding speed from 0.8 to 2.0 m/min. Large amounts of acicular ferrite and lath bainite were formed in the weld metal at a high welding speed, which resulted in an excellent impact toughness.