Analysis on clogging of submerged entry nozzle in continuous casting of high strength steel with rare earth

The type of inclusions in tundish steel and the formation mechanism of the submerged entry nozzle (SEN) clogging in the continuous casting of the rare earth (RE) high strength steel without calcium treatment were studied based on the plant trials and thermodynamic calculation. It was found that Ce2O3 and CeAlO3 in tundish molten steel were transformed into Ce2O2S + CaO–Al2O3 with the size of 2–3 μm during cooling. When the flow velocity of molten steel on surface of the SEN was slow due to the boundary layer effect, Ce2O3 inclusion in molten steel reacted with Al2O3 in the SEN refractory to form CeAlO3. With the continuous erosion of molten steel and reaction, the compositions of CeAlO3, Al2O3 and CaO were aggregated, and the clogging layers with different zones were formed on surface of the SEN. Meanwhile, a small amount of molten steel remaining in the arc zone and corner zone of the SEN formed solidified steel. When calcium treatment is canceled, the reaction probability between inclusions in molten steel and refractory should be reduced by improving the material and shape of the SEN.