Effect of Rb₂O and Cs₂O on Inclusion Removal in 321 Stainless Steels Using Novel Basic Tundish Fluxes

Inclusion removal and modification of the 321 stainless steel using Rb₂O- and Cs₂O-containing novel basic tundish flux has been investigated. The average inclusion diameter was significantly lowered after reaction of the liquid metal with the flux after 45 minutes in an induction furnace set at 1823 K (1550 °C) under an Ar atmosphere. The number of inclusions was also decreased with increased reaction time and the majority of the inherent TiN inclusions were removed after reaction with the proposed novel basic tundish flux. Spinel inclusions were also observed after the reaction, which was due to the reaction of the MgO crucible and the CaO-Al₂O₃-SiO₂-MgO-‘x’wt pct R₂O flux system at fixed CaO/(Al₂O₃ + SiO₂) of 1.45. The Rb₂O and Cs₂O seemed to have allowed significant removal of the TiN inclusions due to its ion compensation effect and the supplement of free oxygen ions, while increasing the viscosity of the slag to retain the absorbed inclusions.