Research on in situ laser cladding of 304 stainless steel coating on Q235 substrate in underwater environment

In this research, 304 stainless steel coating was prepared on the surface of Q235 steel by in situ laser cladding technology in both underwater and in-air environments. The optimal process parameters of laser cladding in the underwater environment were first investigated by using a homemade local dry laser torch. The effects of the laser power, scanning speed, and wire feed speed on macroscopic forming, geometric characteristics, and the microstructure of the cladding layers were investigated. Under the optimal process parameters, the effects of the water environment on macroscopic forming, geometric characteristics, and the microstructure and microhardness of the cladding layers were studied. The results showed that as the environment transferred from underwater to air, the height (H) and cladding angle (α) of the deposited region (DR) decreased, but the fusion width (W) and the depth (h) of the fusion region (FR) increased due to the slow cooling rate and long residence time at high temperatures. For both underwater and in-air cladding layers, the microstructure of DR and FR was equiaxed dendrites and columnar dendrites. Besides, a cellular structure appeared in the FR of the underwater cladding layer. The width of the lathy δ ferrite in the FR in the underwater environment was smaller than that of the in-air environment. Finally, the grain size of the underwater specimen was finer, so the average microhardness value of the in-air specimen was lower than that of the underwater specimen.