Dissolution Behavior of Mg and Ca from Dolomite Refractory into Al-killed Molten Steel

Abstract

Dolomite refractories are widely used in the refining process of clean steel and are considered potential sources of Mg and Ca that form MgO·Al₂O₃ spinel and CaO-containing inclusions. In this study, dolomite refractories were immersed into Al-killed molten steel with either 0.05% Al or 0.25% Al. The dissolution behavior of Mg and Ca from the dolomite refractory was studied, and the inclusion transformation behavior was observed. The results revealed that MgO in the dolomite refractory was reduced by Al in the molten steel, and the Mg content depended on the Al content. On the contrary, CaO barely dissolved into the molten steel even though the Al content increased. After immersion in both the low Al (0.05% Al) and high Al (0.25% Al) steels, an interfacial layer consisting of solid MgO and liquid phase CaO–Al₂O₃–MgO was formed on the surface of the rods. The initial Al₂O₃ inclusions gradually changed into Al₂O₃ saturated MgO–Al₂O₃ spinel after 60 min in low-Al steel; but were quickly transformed into MgO-saturated MgO–Al₂O₃ spinel in high Al steel. No CaO-containing inclusions were detected in the molten steel regardless of the immersion time and Al content.