On the Kinetics of Decarburization of Liquid Iron with Ar-CO-CO₂ Mixtures

Abstract

The decarburization rates of liquid iron have been measured in the vavious Ar-CO-CO₂ mixtures by using the levitation technique. The concentrations of carbon and oxygen change mostly along the carbonoxygen line in equilibrium with Ar-CO-CO₂ mixture under the condition that the oxide film is not formed on the surface of liquid iron. The reaction finishes at a concentration determined by P_CO2/P_CO. The rate has been analyzed by assuming that the mass transfers between the two phases determine the overall reaction rate. The following rate equation has been obtained under the condition of n_C·n_O=constant; -n_c=P_CO2-P_CO^*P_CO^S/K_IⁿC/RT/k_g {1+ (1+P_CO^S/K_IIγ) (P_CO^*/K_III^nC2) } At the high concentration of carbon the decarburization rate is regarded to be controlled by the mass transfer in the gas boundary layer. The rate is gradually reduced, because the resistance of the mass transfer in the metal boundary layer increases and the driving force of the reaction decreases as the concentration of carbon becomes lower. The iron droplet exploded due to the formation of the oxide film on the surface at the high partial pressure of CO₂. For a short period at the beginning, the rapid reaction occurs to reduce both the concentrations toward the equilibrium line of P_CO+P_CO2, in Ar-CO-CO₂ mixture. The reaction can be satisfactorily explained by the mechanism that C-O degassing and decarburization take place at the same time during this stage.