Microstructure characteristic and mechanical property of pulsed laser lap-welded nickel-based superalloy and stainless steel

To evaluate the effects of pulsed laser welding on the microstructure characteristics and mechanical properties of nickel-based superalloy (C-276) and austenitic stainless steel (304) lap-welded joint, the analyses of morphology, microstructure, phase structure, element distribution, tensile-shear strength and microhardness were carried out. The results indicated the unmixed zone was found at the interface between the weld metal (WM) and 304. A small number of inter-dendritic precipitates were also found, and the precipitates were most probably p or μ phases. Compared with the phase structure in C-276, the dominated phase structure in the WM was also austenite phase, however, the lattice constant was reduced due to the decrease of Ni, Mo and W content. The macro-element distribution was inhomogeneous in the WM due to the rapid cooling rate in pulsed laser welding, and the element transition region adjacent to C-276 was wider than that adjacent to 304. The fracture mode of lap-welded joint in tensile-shear test was tensile fracture, and the tensile strength was decreased by 17% compared with that of C-276. The microhardness value in the WM was not lower than that in the base metals.