Effect of tundish flux on reoxidation behavior of Si-killed 316L stainless steel

Abstract

The slag-metal reactions between Si-killed 316L stainless steel and the fluxes rice hush ash (RHA), RHA + CaO–SiO2 (flux A), and RHA + CaO–Al2O3 (flux B) were conducted in an induction furnace at 1773 K to investigate the effects of the various fluxes on the reoxidation behavior of the liquid steel. The total oxygen (T.O) content in the liquid steel increased when the steel reacted with RHA and RHA + A fluxes, whereas T.O decreased when the liquid steel reacted with RHA + B flux. The number density of non-metallic inclusion (NMI) in the steel reacted with RHA, RHA + A, and RHA + B fluxes increases, stays constant, and decreases, respectively. The increase in the number density of NMI is due to the reoxidation of the molten steel caused by the dissociation reaction of SiO2. However, the number density of NMI in the steel decreased since B flux has a higher value of physicochemical factor, i.e., log(ΔC/η), where η is slag viscosity and ΔC represents concentration difference between initial content and saturation limit of target oxide in slag. The reoxidation reaction caused by the presence of SiO2 in the fluxes and inclusion absorption (dissolution) reactions are competitive or coupled each other. Higher SiO2 activity in the fluxes (such as RHA) resulted in easier formation of SiO2-rich inclusions. However, the SiO2 activity in Flux A and Flux B is lower than that in RHA, and the MnO–SiO2 and SiO2 inclusions in the Si-killed steel were reduced by Al to form MnO–SiO2–Al2O3(-Cr2O3) system inclusions in the steels reacted with Flux A and B, respectively.