Influence of tundish flux on reoxidation behavior of Al-killed Ti-containing stainless steel

Abstract

The cleanliness of Ti-containing ferritic stainless steel (Ti-FSS) has been improved via vacuum-oxygen-decarburization (VOD) and ladle treatment (LT) processes. However, the reoxidation phenomena inevitably occur during melt transfer from ladle to continuous casting tundish, resulting in a loss of titanium yield in conjunction with the formation of reoxidative inclusions. Hence, the present work aims to systematically investigate the combinational effect of different tundish fluxes on the reoxidation behavior of Al-killed Ti-FSS melt. Rice husk ash (RHA) and MgO (M) insulation powders, and calcium aluminate, CaO–Al2O3 (CA) based flux were used for the experiments. When the molten steel was covered by M + CA fluxes, the average size of inclusions decreased. On the other hand, when the RHA + CA fluxes were added, the average size of inclusion decreased, whereas total number of inclusions significantly increased due to a reoxidation reaction by SiO2 in RHA. When the M + RHA + CA combinative fluxes were added, the size of inclusion decreased, and the number of inclusions exhibited a value between the M + CA and RHA + CA conditions. Consequently, a decrease in total oxygen content in Ti-FSS was most effective in the M + CA flux combination.