Optimization of continuous casting for preventing the surface peeling defects of Ti-containing ferrite stainless steel

Abstract

Abstract Owing to the durability of stainless steel, stainless steel components can be effectively reused, remanufactured, and indefinitely recycled. The production of stainless steel from scrap is expected to be a trend in the future to achieve a circular economy. However, the surface of cold-rolled Ti-containing ferrite stainless steel strips produced from scrap is prone to severe peeling. In this study, it was found that peeling defects were caused by cracking near slab inclusions during hot rolling. These inclusions mainly comprised Ti oxides, Ti nitrides, and Al oxides generated from clogged and submerged entrance nozzles. To prevent peeling defects and the clogging of the submerged entrance nozzle, the Taguchi method was used and the optimal casting parameters, such as casting overheating, casting speed, stirring time, and inclination, were determined. Increasing casting overheating and decreasing the casting speed inhibited clogging and effectively mitigated peeling defects. When casting overheat was fixed at 60°C with a casting speed in the range of 0.8–0.9 m/min, no peeling defects on the surface of the steel strip were observed. The steel strip produced using the optimized parameters fulfilled the required mechanical properties (tensile strength ≥ 415 MPa, yield strength ≥ 205 MPa, elongation ≥ 22%, and hardness ≤ 89 HRB) and design criteria.