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

Abstract

This study investigates the deformation characteristics of 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–MnO–(CaO–Al2O3) phase has a high proportion of liquid components at 1100–1360 °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%.