Influence of Al/Ti Ratio in Ti-ULC Steel and Refractory Components of Submerged Entry Nozzle on Formation of Clogging Deposits

Abstract

Nozzle clogging during continuous casting of Ti-ULC (Ultra Low C) steel was investigated by inspections of plant -used SENs and laboratory scale experiments using a rotating finger method. Various Alin ratios in the steel and different kinds of nozzles (with or without CaO) were employed. Clog deposits found in the used SENs were composed of complicated oxide (CaO-Al(2)O(3-)TiOx,-...), Fe drops and chunks. Increasing Ti concentration increased amount of the deposit the metallic deposits. In the laboratory scale experiments, increasing Al/Ti ratios was effective to suppress the formation of the deposit and the oxidation loss of Ti in the steel. When a refractory without CaO was used, increasing Al/Ti ratio decreased the portion of Ti oxide in the deposit. Almost no Fe drops were observed, except for a thin layer of Fe on surface of the oxide deposit. When CaO-lined refractory was used, many numbers of Fe drops were found inside the deposit. Increasing Al/Ti ratio lowered Ti peak in the oxide deposit. The present results lend a strong support that Ti-ULC steel is oxidized by CO gas from nozzle refractory, forming FetO-containing liquid oxide and solid alumina. The liquid oxide is reduced to leave Fe drops and AL(2)O(3) TiO, layer. If CaO presents in the nozzle, then a complicated oxide of CaO Al2O3 TiO, forms, as was found in the SEN from the practical operation.