Study on the Oxide Layer and Chromium‐Depleted Layer of Online Solution Annealing Austenitic Stainless Steel

Online solution annealing is suggested as a low‐cost process for hot‐rolled austenitic stainless steel, utilizing residual rolling heat to soften work‐hardened microstructures. However, the coil rolled using the new process exhibits inferior pickling efficiency compared to conventional processing due to variations in oxide layer morphology and chromium‐depleted layer (CDL) formation. The effects of final rolling temperature, air‐cooling time, and coiling temperature on the microstructure of the oxide layer and CDL in 304 austenitic stainless steel are investigated through hot‐rolling experiments. Based on these investigations, the online solution annealing process parameters are optimized to improve the surface quality of the strip after pickling. Higher final rolling temperatures (1020–1060 °C), air‐cooling times of 5–10 s, and lower coiling temperatures (below 500 °C) result in an oxide layer structure that is easier to pickle. Ultimately, an industrial hot‐rolling experiment incorporating online solution annealing is conducted, followed by pickling and cold‐rolling processes. In addition to mechanical properties and resistance to intergranular corrosion, the surface quality of the product is not significantly different from that of the cold‐rolled coil produced by the conventional process.