Process optimization, microstructure, and mechanical property of variable gap weathering steel joints fabricated by oscillating laser-MAG hybrid welding

The welding of weathering steel variable gap joints remains a crucial challenge for bogie manufacturing in the high-speed rail industry. In this study, oscillating laser-metal active gas hybrid welding of the weathering steel variable gap joint was conducted. By adopting the response surface experimental method, well-formed joints across the entire weld, at both small and wide gaps, were successfully obtained. The microstructure at the gap of 0.5 mm and that at the gap of 2.5 mm both consisted of polygonal ferrite, fine acicular ferrite, and a small amount of pearlite. By measuring the grain size and grain boundary angle of the welds at gaps of 0.5 and 2.5 mm, it was found that the grain boundary angle at the gap of 0.5 mm was similar to that at the gap of 2.5 mm, but the grain size at the gap of 2.5 mm was finer. The tensile strength of the welds at different gaps all exceeded that of the base metal. However, the impact energy of the weld at the gap of 0.5 mm was lower than that at the gap of 2.5 mm, and both were lower than that of the base metal. The results of this study provide ideas for optimizing the welding process of weathering steel thick plates with variable gaps.