Transient Behavior of Inclusions during Reoxidation of Si-killed Stainless Steels in Continuous Casting Tundish

Abstract

In the current study, steel samples in continuous casting tundish were taken at every 5–10 minutes to investigate the reoxidation behavior and inclusions in Si-killed stainless steel in the tundish during a casting sequence with three heats. Contours were employed to clearly illustrate the distribution of number density, diameter and area fraction of inclusions in composition ternary diagrams. After reoxidation of Si-killed stainless steel, [Al] and [Ca] in the steel were oxidized and decreased to extremely low levels in the reoxidized region of the molten steel. A large number of MnO-riched small inclusions as transitional products were generated by the oxidation of high [Mn], and gradually decreased. The population density function (PDF) of inclusions tended to a power law type function (f(r)=4.54×10⁻⁵·r^−3.66). Moreover, thermodynamic calculation illustrated that, the increase rate of MnO and SiO₂ content in liquid inclusions are much faster than that of Al₂O₃ and CaO during reoxidation of Si-killed stainless steel, while solid inclusions become predominant and transfer from CaAl₄O₇ to CaAl1₂O₁₉ to Al₂O₃ in Al-killed stainless steel.