Formation Mechanism of High-MnO-Content SiO2/SiO2-MnO-(CaO-Al2O3) Dual-Phase Inclusions in Si-Mn-Killed Steel

This study investigates the deformation characteristics of SiO2/SiO2-MnO-(CaO-Al2O3)-type inclusions in silicon manganese deoxidized steel from continuous casting to rolling. The results reveal that the inclusions contain 60-80% SiO2, 10-35% MnO, and a combined CaO and Al2O3 content of <20%. SiO2 precipitates inside the inclusions during the continuous casting and rolling processes, which results in the formation of pure SiO2/SiO2-MnO-(CaO-Al2O3) dual-phase inclusions in the remaining components owing to the increase in the MnO content to 15-40%. According to the experimental results of melting rate measurement and thermodynamic calculation using FactSage8.1, the SiO2/SiO2-MnO-(CaO-Al2O3) phase has a high proportion of liquid components at 1100-1360 degrees C and exhibits good deformation properties during the breaking down and rolling processes. When the total content of CaO, Al2O3, and MgO in the SiO2-CaO-Al2O3-MgO-MnO inclusions reaches 30-50%, SiO2 precipitation is inhibited during the continuous casting to rolling process. Through the addition of metal manganese and carbon powder during the pre-deoxidation process, followed by alloying with ferrosilicon and metal manganese, and then the addition of acidic synthetic slag for slag formation, the proportion of SiO2/SiO2-MnO-(CaO-Al2O3) dual-phase inclusions in the casting billet is increased from 12% to >60%.