Application of CO2 and O2 Mixed Blowing on the Decarburization and Manganese Retention

Adding high carbon ferromanganese in the early decarburization stage of 200 series stainless steel can reduce the electrolytic manganese added during alloying; however, the oxidation loss of manganese is severe. This paper studies CO2 and O2 mixed blowing thermodynamics and kinetics on decarburization and manganese retention of 200 series stainless steel. The thermodynamic study indicates that manganese oxidation reduces when CO2 is used instead of part of O2 in molten steel decarburization. Meanwhile, the kinetic study determines that more bottom blowing gas enhances the stirring of molten steel by using CO2 and O2 mixed blowing technology; thus, the kinetic condition of decarburization can be improved. The industrial experimental study identifies that the tap-to-tap time increases by 4–5 minutes for every ton of high carbon ferromanganese increased during decarburization by using CO2 and O2 mixed blowing. Compared to pure oxygen blowing, applying CO2 and O2 mixed blowing significantly reduces manganese oxidation in decarburization, increases manganese yield by 3–5.6%, and exhibits a remarkable effect on decarburization and manganese retention.