Suppressing initial clog deposits on inner surface of submerged entry nozzle refractory for casting liquid steel: Absorbing CO gas by CO absorbers

Abstract

A series of experiments and thermodynamic analyses were carried out to find a countermeasure to prevent submerged entry nozzle clogging during continuous casting of Ti-added Ultra-Low C (Ti-ULC) steel, by suppressing CO gas generation in the nozzle refractory. SiO2 and C in usual nozzle refractories proceeded a carbothermic reaction, which generated the CO gas. The CO gas then reoxidized Ti-ULC steel, and a mixture of alumina and FetO-Al2O3-TiOx liquid oxide formed, which was reported to be an initial clog deposit. A concept of "CO absorber" was proposed to absorb the generated CO gas back into the refractory, thereby suppressing the reoxidation. This decreased the thickness of the reoxidation reaction product layer at the interface between the refractory and the steel, which could play as the initial clog deposit. Al4C3, B4C, CaC2, and Al were considered as the candidates for CO absorbers. It was found that B4C was the best candidate thanks to its anti-hydration character, high-temperature stability, and the extent of absorbing CO gas. A series of hot tests were carried out by reacting synthesized refractories in which a certain amount of the candidates were blended. The refractory with 3 mass pct. B4C showed the best result.