On the Deoxidation of Liquid Iron with Silicon

Abstract

The mechanism on the deoxidation of liquid iron with Si was studied on the basis of the various facts obtained by the experiments A, B, and C.
Experiment A; An investigation was made on the change of the oxygen content in liquid iron and the shape and the size distribution of the inclusion, after addition of metallic Si.
Experiment B; The process of growth and the composition of the deoxidation products were studied, after the prompt and homogeneous dissolution of deoxidizer Si or Si-Al.
Experiment C; The mechanism of dissolution of oxygen from the SiO₂ crucible into liquid iron was studied.
The results obtained were summarized as follows.
1) The formation of SiO₂ is not completed immediately after addition of Si and consequently the supersaturation in liquid iron occurs until the equilibrium is reached.
2) It was concluded that the growth of the oxide particle or the deoxidation reaction was not controlled by the diffusion of the solute atom, but the reaction rate at the particle surface, and in general the local equilibrium was not maintained there even at steelmaking temperature.
3) The ratio of the rate constant for the reaction Si+2O→SiO₂, 2Al+3O→2Al₂O₃ was estimated by means of the composition of the products obtained by the Si-Al deoxidation in the experiment B. The ratio was constant in a wide range of the concentration of aluminium, silicon and oxygen in liquid iron.
4) In the experiment A, the greater part of the primary inclusion floats out rapidly and the total oxygen agrees nearly with the dissolved oxygen 5 minutes after addition of silicon.
5) The mechanism on the formation of the inclusion during solidification was discussed from the point of view of nucleation and growth of the oxide particle.