Kinetics of Decaburization of Low Carbon Liquid Iron under Reduced Pressures

Abstract

The kinetics of decarburization of liquid iron by blowing Ar-CO-CO₂ gas mixtures under reduced pressure have been studied using a vacuum induction furnace containing 12 kg metal at 1 600°C.
The results obtained are as follows:
1) In low carbon concentration range, the behavior of decarburization reaction was divided into three types.
(a) In the range of carbon content higher than about 200 ppm, the rate of decarburization was described as the zeroth order reaction with respect to [C]. "Region-0".
It was concluded that the rate-determining step was decomposition of CO₂ chemisorped at liquid iron surface. Then, the apparent rate constant of the reaction was equal to 2.5×10^-3 [mol/cm²·s]=0.43[cm·%/s·atm].
(b) In the range of carbon content between 10 ppm and 200 ppm, the rate of decarburization was described as the first order reaction with respect to [C]. "Region-I".
As the rate constant decreased with increase in [S] content, it was concluded that the rate of decarburization was controlled by mass transfer of carbon in diffusion boundary layer in the metal and the chemical reaction of CO gas formation at the metal surface.
(c) In the case of carbon content less than 10 ppm, the rate of decarburization was less than that in "Region-I". "Region- II ".
2) In each region, the adsorption coefficients of sulfur at 1 600°C were given as follows,
"Range-0": κ_s=65, "Range-I": κ_s= 5063