Rates of Nitrogen and Carbon Removal from Liquid Iron in Low Content Region under Reduced Pressures

Abstract

The kinetics of nitrogen and carbon removal from a liquid iron surface in low content regions by blowing Ar gas mixture under reduced pressures have been studied using the same vacuum induction furnace at 1 600°C, respectively. The results obtained are as follows:
(1) The nitrogen removal reaction is described as a second order reaction with respect to nitrogen content. The overall reaction rate constant, k_ov^N, decreases with the increase of total pressure, and oxygen and sulfur content.
Assuming that the nitrogen removal reaction progresses by a mixed control and that the chemical reaction for nitrogen gas formation is caused by adsorbed nitrogen atoms, the chemical reaction rate constant, k_r^N, and the adsorption coefficient of oxygen, κ_O, and of sulfur, κ_S, are estimated as follows:
N+N=N₂+_??_
k_r^N(=k_[N]/f_N²) cm/mass%/sec = 15/(1+κ_O·a_O+κ_S·a_S)²,
κ_O=161, κ_S=63.4
In the Fe-20mass%Cr-0.2Mass%C-S system also, the value of k_r^N can be expressed by the same equation. It is thus concluded that, macroscopically, the mechanism of nitrogen removal is the same irrespective of whether or not the melt contains chromium.
(2) In the carbon content range below 200 ppm, the overall carbon removal reaction rate constant, k_ov^C, exhibits a maximum value against oxygen content, and decreases with the increase of sulfur content.
Assuming that the chemical reaction for CO gas formation caused by the adsorbed carbon and the adsorbed oxygen atoms as a following equation, the dependence of the chemical reaction rate constant on oxygen and sulfur content is explained by the values of the adsorption coefficients κ_O and κ_S, respectively.
C+O=CO+_??_
The value of κ_O is equal to about 100-300 and that of κ_S is equal to about 40-65.
These values are in general accord with those determined from the nitrogen desorption reaction.