1995 Volume 81 Issue 12 Pages 1109-1113
Recently a new process has been developed to control the γ-α transformation of steels using MnS precipitates on the oxide inclusions as nuclei. In order to optimize the composition of inclusions, phase relations for the MnO-SiO2-MnS system have been investigated at temperatures ranging from 1473K to 1723K. The solubility of MnS increased with an increase in MnO/ (MnO+SiO2) ratio and showed a drastic increase at the ratio of 0.6, which was consistent with the maximum precipitation ratio of MnS in the oxide metallurgy process. An oxysulfide compound composed of 8MnO·3SiO2·MnS was newly found as a stable solid phase at lower temperature than 1573K. It has been considered that this phase is formed via the peritectic reaction between 2MnO·SiO2 and liquid phase. Deliberating the compositions of liquids saturated with various compounds at several temperatures, the phase diagram for the MnO-SiO2-MnS system has been estimated. Finally, the mechanism of the MnS precipitation in the oxide inclusions has been discussed.
