Phase Equilibria between SiO2 and Iron-Chromite Spinel Structure Solid Solution, and Deoxidation of Liquid Fe-Cr Alloy with Silicon.

Abstract

Oxygen control in liquid stainless steel production is extremely important for the removal of impurities and improvement of Cr yield. Precise information on the thermodynamics of oxygen in liquid Fe-Cr alloy is necessary for this purpose. The equilibrium relation between dissolved Cr and O in liquid iron saturated with pure solid Cr 2 O 3 or FeO.Cr 2 O 3 solid solution and thermodynamic behavior of FeO.Cr 2 O 3 solid solution had been established in our previous works. Following these studies, the deoxidation equilibrium of Si in liquid Fe-Cr alloy was thermodynamically discussed in this paper. Mutual solubility between SiO 2 and (Fe,Mg)O. (Cr,Al) 2 O 3 solid solution was observed at 1 573 and 1 873 K, in order to know the activity of SiO 2 coexisted with Cr 2 O 3 based oxide solid solution after Si deoxidation of liquid Fe-Cr alloy. It was found that Si deoxidation equilibrium of liquid Fe-Cr alloy could be thermodynamically evaluated based on unit activity of SiO 2 due to negligibly small mutual solubility between SiO 2 and Fe t O-Cr 2 O 3 based solid solution. As the result, the deoxidation power of Si would not enough high to produce low oxygen high Cr steel because of the attraction between Cr and Si in liquid iron.