Formation and Removal Mechanism of Globular Oxide Inclusions in Low‐Carbon Aluminum‐Killed Steel: Thermodynamic and Kinetic Analysis

Globular oxide inclusions exert a considerable repercussion on the product reliability of low‐carbon aluminum‐killed steel. In this study, the mechanisms underlying the formation and removal of globular oxide inclusions in low‐carbon aluminum‐killed steel during steelmaking were explored by means of an industrial trial. During the early stage of Ladle Furnace (LF) refining, the molten steel predominantly contained clustered Al 2 O 3 inclusions. As refining progressed, the inclusions transformed into irregularly shaped MgO–Al 2 O 3 . Following RH calcium treatment, the impurities in the molten steel were converted into low‐melting‐point CaO–MgO–Al 2 O 3 inclusions. These low‐melting‐point inclusions remained suspended in the steel. Their persistence is identified as the principal reason for the excessive occurrence of globular oxide inclusions. The emergence of dissolved magnesium in the steel is the fundamental cause of this transformation. Thermodynamic calculations indicate that throughout the entire refining sequence, the refractory serves as the predominant source of magnesium transfer into the steel. Kinetic calculations further demonstrate that the removal rate of MgO–Al 2 O 3 inclusions from the steel is more rapidly than that of low‐melting‐point CaO–MgO–Al 2 O 3 inclusions. This is primarily attributed to the substantially lower interfacial tension of the low‐melting‐point CaO–MgO–Al 2 O 3 inclusion with the steel relative to that of the MgO–Al 2 O 3 inclusion.