关键词: 304L不锈钢, 氨分解气氛, 光亮退火, 晶间腐蚀, 表层渗氮

Abstract: The bright annealing process of solid-solution treated 304L stainless steel plate in 800 ℃ ammonia decomposition atmosphere (1050 ℃ for 15 min with slow cooling) was simulated, and the microstructure and corrosion resistance were characterized and analyzed. The results show that a fine grain structure and chromium-rich nitrides are formed at the surface layer (about 5 μm from the surface), while the chromium-rich carbonitrides are precipitated at the grain boundaries in the subsurface layer (about 40 μm from the surface). The microhardness of the surface and subsurface layers are (318.0±9.0) HV0.05 and (220.9±12.3) HV0.05, respectively, both exceeding the matrix hardness of (187.8±9.2) HV0.05. Before sulfuric acid-iron sulfate hot dipping for 24 h, the average corrosion rate of the surface layer is 0.016 mg/(mm²·h). After 24 h of hot dipping, corrosion starts to occur in the stainless steel matrix, with the average corrosion rate decreasing to 0.006 mg/(mm²·h). Nitrogen atoms generated from the residual ammonia decomposition diffuse inward from the surface and along the grain boundaries, promoting nitrogen diffusion into the surface layer and slight sensitization in the subsurface layer, which increases the susceptibility to intergranular corrosion.

Key words: 304L stainless steel, ammonia decomposition atmosphere, bright annealing, intergranular corrosion, surface nitriding