Thermodynamic Calculation and MnS Solubility of Mn-Ti Oxide Formation in Si-Mn-Ti Deoxidized Steel

Mn-Ti oxides in Si-Mn-Ti deoxidized steels after cooling in the furnace were investigated. The composition and morphology of inclusions were analyzed by using FE-SEM with EDS. Mn-Ti oxides were found to be effective sites to induce intragranular ferrite formation. The thermodynamic calculation was employed to interpret the critical condition for Mn-Ti oxide formation. Mn-Ti oxide formation was controlled not only by Mn and Ti content, but also by total oxygen content in steel. When the Mn and Ti contents were around 1.5% and 0.005%–0.01%, respectively, Mn-Ti oxide could form as the total oxygen content was 0.001%–0.002%. The experimental results were in good agreement with thermodynamic calculation results. Also, MnS solubility was examined in Mn-Ti oxide inclusion system. With an increase of MnO content in Mn-Ti oxide, MnS solubility in the oxides increased. MnS precipitation benefited from high MnO content in Mn-Ti oxide.