Formation Mechanism of Ca-Si-Al-Mg-Ti-O Inclusions in Type 304 Stainless Steel

Abstract

Inclusions of CaO-SiO₂-Al₂O₃-MgO-TiO₂ in type 304 stainless steel were found to be formed by Al and Ti deoxidation on nucleation sites of suspended AOD slag droplets in molten steel. The crystallized phases in inclusions, i.e., MgO·Al₂O₃ spinel, CaO·TiO₂ (perovskite) and TiO₂ (rutile), showed very high melting temperature and formed in parallel to the decrease in molten steel temperature. The major factors affecting MgO·Al₂O₃ spinel crystallization are aluminum content in steel and weight fraction of MgO in AOD slag. Also, decreasing the AOD slag basicity (%CaO/%SiO₂) is the most effective way to reduce the crystallization of the harmful CaO·TiO₂ phase in inclusions.