To investigate the corrosion behaviours of different refractories (MgO and Al 2 O 3 ) by Al-killed liquid steel after calcium treatment, high-temperature experiments were carried out in laboratory with different Ca additions. The phases and the composition of the reaction layer at the refractory-steel boundary were analysed, and its thickness was measured. It was found that, when the MgO refractory contacted with the liquid steel, a thin MgO-Al 2 O 3 layer was generated without Ca addition. When the Ca content in steel increased to 28 ppm, a dotted (even a continuous) CaO-Al 2 O 3 layer was formed on the edges of the MgO and Al 2 O 3 refractories, with its thickness reaching up to 695 μm. Vaporized Ca gas also caused evident corrosion of refractory, producing CaO as the reaction product. In addition, the microstructure of the refractory influenced the corrosion of the refractory as well, and less porous refractory had weaker corrosion. Due to the corrosion of refractory, the spalling of the refractory grains and the detachment of the CaO-Al 2 O 3 reaction layer both would lead to the formation of large-sized inclusions in steel. Therefore, the addition amount of Ca should be strictly controlled during calcium treatment.
Zhang et al. (Wed,) studied this question.