Rate of decarburization of iron-carbon melts: Part II. a mixed-control model

Abstract

The observed retarding effect of sulfur on the decarburization of Fe-C melts has been interpreted by means of a mixed-control mechanism involving gas-phase mass transfer and dissociative adsorption of CO₂. A mathematical model formulated on the basis of the proposed mechanism gave an excellent fit to the experimental data. The application of the model to the data provided a value of 4.42 x 10⁻³ mole · cm⁻² · s⁻¹ · atm⁻¹ for the dissociative adsorption rate constant for CO₂ on liquid iron at 1973 K; the fraction of surface sites that cannot be occupied by sulfur, even at apparent surface-saturation, was found to be 0.085. The model predicts a residual rate of decarburization at high sulfur concentrations; this prediction is borne out by the experiment. The effect of convective motion within the levitated melt on the rate of decarburization below a characteristic carbon concentration was quantified. The liquid-phase mass transfer was greatly enhanced by the stirring effect of the electromagnetic field. The effective diffusivity of carbon in Fe-C melts under levitation conditions has been found to be 3.24 x 10⁻³ cm² · s⁻¹, a value ten times as large as that under stationary conditions.