Novel mechanism for the modification of Al₂O₃-based inclusions in ultra-low carbon Al-killed steel considering the effects of magnesium and calcium

Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al₂O₃-based inclusions during secondary refining. The results showed that Al₂O₃-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition,Mg in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO-MgO-Al₂O₃ multi-component inclusions. Thermodynamic analysis confirmed that the reaction betweenMg and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3wt% and the temperature is higher than 1843 K.