Effect of laser spot offset on microstructure and properties of laser welded joint of medium Mn/DP980 dissimilar steel

During laser welding of medium Mn (M-Mn) steel, the existence of Mn element at the grain boundaries (GBs) lead to the embrittlement of the joint. In this paper, a new strategy of dissimilar high strength steel welding and laser spot offset is introduced in the laser welding of M-Mn steel. This paper focuses on the influence of laser spot offset on the brittleness of laser welded joints of M-Mn/dual-phase 980 (DP980) dissimilar steel, and compares the differences in microstructure, element distribution and properties of joints under different processes. Compared with the welded joints of M-Mn/M-Mn steel and M-Mn/DP980 steel, the content of Mn element and Mn23C6 carbide in the GBs of the new welded joint was reduced, which greatly slowed down the propagation of intergranular cracks in the fusion zone (FZ). Finally, the plasticity of the welded specimen is greatly improved.