Effect of CaO–MgO–SiO₂–Al₂O₃–TiO₂–CaF₂ Slag Composition on Inclusions in Ti-Stabilized 20Cr Stainless Steel

Abstract

Laboratory experiments and thermodynamic calculation for the Al-killed Ti-stabilized 20Cr stainless steel with several CaO–MgO–SiO₂–Al₂O₃–TiO₂–CaF₂ slags containing different CaF₂ contents were performed to investigate the effect of slag composition on inclusions in molten steel. The titanium and magnesium contents were higher in the steel samples reacted with the slag samples containing higher CaF₂ contents. The thermodynamic results based on the ion and molecule coexistence theory (IMCT) also indicated that the log (a²_SiO2/a_TiO2), log(a²_Al2O3/a³_TiO2) and log(a_Al2O3/a³_MgO) decrease with the increase of CaF₂ content in slag, which would make the molten steels have higher titanium and magnesium content. The increase of magnesium content in steel due to the increase of CaF₂ in slag led to the increase of MgO content of inclusions. Due to the highest CaF₂ content in slag, some inclusions in the steel were located in (liquid + MgO + TiSp) phase field. Reducing the CaF₂ content in slag to 5.18 mass%, the MgO content of inclusions in steel was reduced, which made most of the inclusions located in or close to liquid oxide phase field. The reasonable CaF₂ content in slag was discussed with the consideration of controlling the titanium content and the formation of inclusions in molten steel.