2019 Volume 105 Issue 11 Pages 1042-1049
The effect of Al addition in the middle of the metal-slag reaction on the formation of MgO·Al2O3 spinel-type inclusions was investigated by laboratory-scale experiments and a kinetic model calculation in order to reduce the spinel-type inclusions in high-carbon steel. As results of the experiments, the total Mg content in the steel and average content of MgO in the inclusions were relatively low before Al addition, and spinel-type inclusions were hardly formed. After Al addition, spinel-type inclusions formed when CaO/SiO2 and CaO/Al2O3 in the slag were high, and the total Mg content in the steel and average MgO content in the inclusions were also higher. On the other hand, formation of spinel-type inclusions was suppressed at lower CaO/SiO2 and CaO/Al2O3 in the slag. Therefore, the experimental results indicated that addition of Al at the midpoint in the reaction and control of the slag composition were effective for suppression of spinel-type inclusions. However, spinel-type inclusions formed soon after Al addition in slag with higher CaO/SiO2 and higher CaO/Al2O3. To evaluate the effect of midpoint addition of Al on the actual process, a kinetic model calculation under virtual conditions was carried out. According to the calculation, the increase in the content of Mg in the steel under actual-scale conditions was slower than that in the laboratory, and formation of spinel-type inclusions could be avoided.