Abstract:   The surface defects of cold-rolled SUH409L stainless steel sheet were analyzed by scanning electron microscope.  The results indicate that the defects are caused by complicate oxides of CaO·TiO₂-MgO·Al₂O₃.Analysis of the rules of inclusion evolve, these inclusions were deoxidation products during the steelmaking. The deoxidation products which attached to the inner wall of the nozzle as the affect of molten steel flowing were captured by the solidification slab shell in the mold. The defects were caused by these subsurface inclusions during the cold rolled process. The formation of CaO·TiO₂-MgO·Al₂O₃ inclusions can be prevented by controlling the appropriate content of aluminum in steel from the point of the mechanism of the inclusion formation, which can reducing the slag oxidizability and avoiding oxidation of titanium in steel. By the way of optimization of steelmaking process, the proportion of cold rolled laminated defects decreased from 1.294 % to 0.259 % .

Key words: inclusion, SUH409L stainless steel, cold-roll sheet, continuous casting