Evolution behaviour of nonmetallic inclusions in Ti-bearing 11 Cr stainless steel with calcium treatment

摘要

Nonmetallic inclusions formed during the Ti-stabilized stainless steelmaking process can induce the clogging in the submerged entry nozzle during continuous casting. To investigate the formation mechanism of nonmetallic inclusions in Ti-stabilized stainless steel, steel specimens were taken at different stages in industrial trials. The characteristics of inclusions and the chemical compositions of steel were analysed. After 10 min of Al deoxidation, the main type of inclusions in samples was irregular MgO-AI_2O_3. With titanium addition after calcium treatment, the irregular dual phase CaO-TiO_x-AI_2O_3-MgO inclusions were formed. The steel compositions of most samples were located in or close to the AI_2O_3-TiO_x liquid oxide phase field. According to experiment and thermodynamic results, the solid CaTiO_3 and/or Ca0-2AI_2O_3 inclusions were formed during titanium addition when the molten steel contained more than 20 ppm calcium. The effect of the initial calcium content on the formation of Ca-AI-Ti-O inclusions during titanium addition was discussed.