Control of Non‐metallic Inclusions by Slag‐metal Reactions for High Strength Alloying Steels

A laboratory study was carried out to investigate non‐metallic inclusions in high strength alloying steel refined by high basicity slag. The results indicated that the inclusions were mainly of the CaO? MgO? Al₂O₃ system, Al₂O₃? MgO and MgO‐based inclusions. The steel/slag reaction time and Al₂O₃ content in slag had a great effect on inclusions characteristics. With the reaction time increasing from 30 to 180 minutes, inclusions experienced a transformation process: from mainly Al₂O₃? MgO system and MgO‐based inclusions to spherical CaO? MgO? Al₂O₃ system inclusions surrounded by a lower melting temperature surface layer of CaO? Al₂O₃. Formation and transformation mechanisms of the inclusions were given based on the results. It was also found that with Al₂O₃ content in slag reduced from 40% to 30%, [Mg] contents in steel melts were increased and MgO in slag reached saturation, which contributed to the formation of more MgO‐based inclusions and a more scattered inclusion composition distribution after 90 min reaction.