After the equilibrium between molten iron and the systems FeO-MnO-SiO₂ and FeO-MnO-CrO-SiO₂ was established in the silica crucible at 1650°C, the temperature was lowered rapidly to 1550°C and this temperature maintained till the equilibrium was attained again. The variations of the concentration of the components in the liquid iron and slag were measured. The results obtained are summarized as follows:
1) MnO and FeO were reduced in the system FeO-MnO-SiO₂ slag by the excess silicon due to the lowering temperature at more than 0⋅18%, manganese in the liquid iron. The relation between reduction ratio of MnO and the concentration of silica was estimated. Up to 0⋅18% manganese, this excess silicon, however, was not sufficient to deoxidize, MnO was not reduced in this case.
2) FeO, MnO and CrO were reduced in the system FeO-MnO-CrO-SiO2 slag by the excess silicon same as the system FeO-MnO-SiO₂ in the case of 5%Cr. But in cases of 9% and 14% Cr, the reduction of these oxides did not occur. It was considered that the new phase was formed at the boundary of both phases.
3) It was anticipated from the experimental results obtained above that the equilibrium between inclusion and molten iron was established fast. The mechanism of the formation of oxide inclusions composed of FeO-MnO-SiO₂ system were examined experimentally by addition of deoxidizers. The results showed that if the processes of formation of oxide inclusions composed of FeO-MnO-SiO₂ system were examined experimentally by addition of deoxidizers. The results showed that if the processes of formation of inclusions could be known, based on the equilibrium data, the components of inclusion could be evaluated from the concentration of dissolved elements in the liquid iron.