9th ECCC European Continuous Casting Conference – ECCC 2017

Rice husk ash on the molten slag is usually composed of solid powder layer, sintered powder layer and interface between the molten slag and sintered powder layer in continuous casting tundish. Because the complicated reaction at the molten slag-sintered powder interface has not been well understood, we investigated the effect of rice husk ash on the reoxidation of molten steel as well as on the corrosion of magnesia refractory. The increase in the ratio of rice husk ash (RHA) to carry-over ladle slag (LS) resulted in the severe reoxidation of molten steel. The increase in the silica activity in the slag layer promoted the self-dissociation of SiO2 from the slag layer into the molten steel. Thus, the silicon and oxygen pick-up occurred as the RHA/LS ratio increased. The oxygen pick-up in the molten steel as well as a decrease in inclusion absorption behavior of molten slag by increasing the RHA/LS ratio caused the formation of Al2O3-rich inclusion in the steel. The spinel inclusions was also formed in the steel by the dissolution of Mg from the molten slag into the steel, which was promoted due to the corrosion of MgO refractory. MgO in the refractory directly dissolved into the slag layer without forming any intermediate compound layer (e.g. spinel) at slag-refractory interface. A slag flow potentially induced by the evolution of gas bubbles at the solid powder-slag-refractory interface accelerated the corrosion of MgO refractory with increasing RHA/LS ratio. Hence, the reoxidation of molten steel in tundish, which causes the formation of alumina-rich inclusions, as well as the corrosion of MgO refractory become more serious as the casting sequence increases.