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 Cr2O3 or FeO · Cr2O3 solid solution and thermodynamic behavior of FeO · Cr2O3 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 SiO2 and (Fe,Mg)O · (Cr,Al)2O3 solid solution was observed at 1573 and 1873 K, in order to know the activity of SiO2 coexisted with Cr2O3 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 SiO2 due to negligibly small mutual solubility between SiO2 and FetO-Cr2O3 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.