Influence of ferrosilicon addition on silicon-oxygen equilibria in high-silicon steels

The role of impurities introduced to the steel melt through ferrosilicon addition is of considerable importance in determining the steel cleanness of Si-killed, Si-alloyed steel grades. The silicon requirement is often met with FeSi addition at the industrial scale. In the present study, a detailed investigation of commercial purity ferrosilicon (FeSi) alloy has been conducted to assess its impurity content. Aluminium and titanium were found to be the main impurities among others. Si-O equilibria in liquid steel has been established at 1873 K using FeSi alloy for a wide range of silicon concentration to examine the influence of its impurities. The actual Si-O equilibria established through FeSi addition was compared with true Si-O equilibria which was established using High-purity silicon (HPS) addition. It has been observed that impurities (mainly aluminium and titanium) from FeSi perturbed the true Si-O equilibria. Thermodynamic and kinetic considerations pertaining to this deviation have been elaborated in the present study.