Oxidation behavior of silicon and carbon in molten iron-carbon-silicon alloys with carbon dioxide

Desiliconization of molten Fe-Si-C alloy is important to keep basicity of slag higher in the dephosphorization process and to minimize total slag generation rate in steelmaking process. However, there is a desiliconization limit because competitive decarburization reaction proceeds as silicon content of metal decreases. Therefore development of an effective method that promotes desiliconization without decarburization is desired. Oxidation behavior of silicon and carbon in molten Fe-C-Si alloys with CO2 is investigated mainly at 1573K in this study. Desiliconization limit with CO2 at 1573K is [mass%Si]=9.1×10-4 under the conditions of ac = 1, aSiO2 = 1 and PCO2 = 1 atm and silicon in metal can be removed up to [mass%Si]=1.3×10-3 in the present experiment. However, in order to remove silicon to a desired level, it is necessary to remove formed SiO2 from the metal bath because SiO2 is reduced with carbon in the melt and Si is remelted into metal. Overall rate constant of silicon oxidation under the condition of ac = 1 is about 3.1×10-5 m/s and is independent of CO2 flow rate. Overall rate constants of simultaneous carbon and silicon oxidation under the condition of PCO2 = 1 are 4.0×10-6 m/s and 5.0×10-6 m/s, respectively and the rate constant for silicon is smaller than that under the condition of ac = 1. It is inferred simultaneous oxidation of carbon and silicon causes some retarding effects on the advance of each reaction.