Influence of Slag and Refractory Materials on Inclusions during the Ladle Refining of Low Carbon Aluminum Killed Steel

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 degrees 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.