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

Abstract

Abstract 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Al 2 O 3 system, Al 2 O 3 MgO and MgO‐based inclusions. The steel/slag reaction time and Al 2 O 3 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 Al 2 O 3 MgO system and MgO‐based inclusions to spherical CaOMgOAl 2 O 3 system inclusions surrounded by a lower melting temperature surface layer of CaOAl 2 O 3 . Formation and transformation mechanisms of the inclusions were given based on the results. It was also found that with Al 2 O 3 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.