Microstructure and properties of 304 stainless steel coating by local dry underwater laser cladding with filler wire

In the air and underwater environment, 308L stainless steel was clad on the surface of Austenitic 304 stainless steel with self-developed underwater laser cladding equipment to explore the repair of 304 stainless steel with defects in underwater environment. The microstructure, chemical composition and phase composition of the coating were analyzed by XRD, EDS and optical microscope. The hardness of the coating was tested by microhardness tester. The electrochemical corrosion behavior of the coating was studied by potentiodynamic polarization and AC impedance spectroscopy. The results show that single layer and multi-channel cladding layers were prepared in two environments, and there were no obvious pores, cracks and other defects. The microstructure of the cladding layer is mainly composed of austenite, ferrite and martensite. Because of the different microstructure and grain size in each region, the hardness of the cladding layer presents a stepped distribution. The coatings in both environments show obvious passivation behavior in 3.5% NaCl solution, and the corrosion resistance of the coatings in both environments is similar. The designed underwater laser cladding with filler wire process meets the requirements of practical engineering for efficient preparation, forming quality and corrosion resistance of cladding layer, and can be used for surface protection and repair of 304 stainless steel in underwater environment.