Microstructure, element distribution and interfacial properties of laser welded iron–nickel–steel dissimilar joints

Reliable connections between cast iron and steel are achieved through laser welding using nickel-based alloy filler wire, which expands the application fields and reduces cost in engineering projects. In this study, the microstructure and element distribution and interface properties of laser welded metal (WM) with mixed Iron-Nickel-Steel and heat affected zone (HAZ) of the dissimilar joints were investigated experimentally. Columnar dendrites growing along the temperature gradient were observed in the laser molten pool. Energy dispersive spectroscopy analysis reveals significant microsegregation, with Ni enriched in the upper region of the weld pool and Fe concentrated in the lower region. Furthermore, Cr, Nb, and C exhibit pronounced segregation at grain boundaries, as explained by nonequilibrium solidification theory. The microhardness remained relatively stable in the weld material but was significantly higher than that in HAZ, which can be attributed to solid solution strengthening and fine grain strengthening. The joint area had ultimate tensile strength comparable with cast iron but relatively lower elongation. The fracture exhibited a mixed mode, transitioning from brittle to ductile, which outperforms the purely brittle fracture behavior of cast iron.