Effect of mixed gas top blowing on decarburization and manganese evaporation of steel melt in low carbon content range

Experimental and theoretical studies have been carried out to clarify the effects of mixed gas top blowing on decarburization and manganese evaporation of steel melt in low carbon content range. 20 kg scale of induction furnace was used for decarburization experiment. Oxygen utilization efficiency for decarburization increased with an increase in inert gas flow rate and a decrease in oxygen flow rate of mixed gas top blowing. Decarburization rate below carbon content of 0.03 mass% depended on CO partial pressure caused by mixed gas of oxygen and inert gas. To explain these results, an index, IM for decarburization was introduced. The IM is found to be inversely proportional to the oxygen utilization efficiency for decarburization in the low carbon content range, and there is a good correlation between the IM and oxygen content in steel melt. Unexplained manganese content, which seems to depend on its evaporation, decreased with an increase in inert gas ratio of top blowing to oxygen. Manganese evaporation rate was introduced according to Hertz-Knudsen-Langmuir's equation which showed an increase with increasing temperature. Assuming that manganese evaporation occurs at the fire spot caused by top blowing during the final stage of refining, the temperature of the fire spot was estimated to reach 2890K for oxygen top blowing, and decrease to 2475K for mixed gas blowing of (Ar+N₂)/O₂=2/1.