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The evolution of inclusions in low carbon Al killed steel during ladle refining of was studied based on industrial experiments, in which high basicity slag was used. The results showed that inclusions experienced the changes from Al₂O₃ → MgO-Al₂O₃ → CaO-MgO-Al₂O₃ → CaO-Al₂O₃. Without calcium treatment, MgO-Al₂O₃ inclusion in steel were largely transformed into CaO-MgO-Al₂O₃ or CaO-Al₂O₃. With the aim to decrease MgO-Al₂O₃ inclusions and to clarify the effects of refining slag and refractory materials on inclusions, laboratory experiments were performed with lower basicity refining slag (lower basicity slag theoretically helps reduce spinel-type inclusions) in MgO and Al₂O₃ crucibles. The results indicated that, the dissolved Al in liquid steel would react with MgO and CaO in slag or in refractory at 1600 °C. Hence, [Mg] and [Ca] would be supplied into bulk steel. Due to the large contact area between MgO-based refractory and steel, as well as the higher activity of MgO in the refractory, Mg can be more easily reduced, which accounts for the easy modification of Al₂O₃ into MgO-Al₂O₃. By contrast, because of the limited supply of [Ca] to steel, modification of MgO-Al₂O₃ into CaO-MgO-Al₂O₃ or CaO-Al₂O₃ was incomplete. With the use of Al₂O₃-based refractory and reefing slag basicity of about 2.45, MgO-Al₂O₃ inclusions were obviously decreased.