Effect of the laser welding thermal process on the microstructure evolution and corrosion resistance of deformed austenitic stainless steel joints

Abstract

In order to satisfy the requirements of various structure and manufacturing process, the machining processes would be applied to the two components of the joint structure, resulting in a significant thickness disparity between them. Additionally, the heat transfer during laser welding can affect the microstructure of the joint. Therefore, this study investigated the microstructural evolution and corrosion resistance mechanisms of the laser-welded 304 water pipe parent material and receiver parent material. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), potential dynamic polarization analysis, and electrochemical impedance spectroscopy (EIS) were utilized in this study. According to research, the internal structure of the stainless steel nozzle was significantly changed after a high-temperature thermal cycle during laser welding. Recrystallization occured within 254 μm of the fusion line, leading to the formation of equiaxed crystals with fine grains. Due to the reversibility of the martensitic transformation, most of the martensite reversely transformed to austenite within the range of 254– 278 μm of the fusion line. In the region beyond 278 μm from the fusion line, the degree of martensite reverse transformation was minimal. Compared to the nozzle parent material that was deformation processed twice before welding, the volume fraction of martensite after welding is lower, resulting in a slower corrosion rate and higher corrosion resistance. Furthermore, it was found that the welded joints exhibited superior corrosion resistance compared to the cold-rolled nozzle parent material, while the cold-rolled, stamped, and deep-drawn nozzle parent material showed the lowest corrosion resistance.