Purification role and corrosion mechanism of MgO–CaO refractory in stainless steel refining

Abstract In actual stainless steel refining application, the purification effect of MgO–CaO refractory is significant, however, MgO–CaO refractory that only contact with stainless steel and not with slag still experience a certain degree of corrosion. Based on this phenomenon, the purification role of MgO–CaO refractory on molten stainless steel and the corrosion mechanism of MgO–CaO refractory by molten stainless steel were investigated through immersion experiment and the thermochemical simulation software FactSage. The molten stainless steel is purified through the adsorption of liquid sulfide inclusions by the MgO–CaO refractory with subsequent CaO dissolution into the liquid phase. When the concentration of CaO reaches the critical point, CaS precipitates on the surface in the solid form. Moreover, the corrosion of MgO–CaO refractory by stainless steel is through the reactions between CaO and SiO 2 from the oxidized [Si], forming Ca 3 SiO 5 and Ca 2 SiO 4 , creating a 778 µm‐deep corrosion layer. These two processes mentioned above occur simultaneously, leading to the formation of a localized liquid isolation layer. After the immersion experiment, the number of inclusions decreased by 71.4%, while the Si, S, and O contents dropped by 67.9%, 64.5%, and 80.9%, respectively. Finally, the comprehensive reaction behavior of MgO–CaO refractory in molten stainless steel was proposed.