Effect of TiO2 Addition in Ladle Slag on Evolution of Nonmetallic Inclusions in Ti-Bearing Al-Killed Steel

Abstract

To investigate the effect of TiO₂ in refining slag on the nonmetallic inclusions in Ti-bearing Al-killed steel, industrial studies are conducted with and without TiO₂ addition in refining slags. It is found that a suitable addition of TiO₂ (around 5 pct) can improve the fluidity of the slag. When using TiO₂-containing slag, the Ti content in steel increases to 72 ppm after LF refining due to [Ti]-[O] equilibrium, and the yield of Ti-Fe alloy also climbs from 86.5 to 96.3 pct in RH refining even with a lower addition amount. The inclusions generally transform from Al₂O₃ into solid MgO-Al₂O₃ and even liquid CaO-Al₂O₃ inclusions. Although a small amount of TiO_x is generated in inclusions at the middle stage of LF refining due to the effect of TiO₂-containing slag, solid MgO-Al₂O₃ inclusions are still the dominant inclusions in steel after RH refining. Therefore, the suitable addition of TiO₂ does not evidently influence the evolution of inclusions. As a result, it can hardly weaken the removal efficiency of inclusions, while the cleanliness of steel is in fact improved. Lower total oxygen and nitrogen contents are obtained, and the number density of inclusions decreases from 31.7 mm⁻² to 25.0 mm⁻².