Formation and Evolution of Oxide Inclusions in S32750 Duplex Stainless Steel during Argon‐Oxygen Decarburization‐Ladle Furnace Refining

The formation and transformation of oxide inclusions in S32750 stainless steel with different Al contents during argon‐oxygen decarburization‐ladle furnace (AOD‐LF) refining are studied based on industrial trials, inclusion characterization, and thermodynamic analysis. The inclusions at LF arrival stage are CaO–SiO 2 –MgO–Al 2 O 3 –CaF 2 inclusions originated from slag entrainment and the newly formed CaO–SiO 2 –MgO–Al 2 O 3 inclusions which are the products of the chemical reactions caused by the increased Al content and reoxidation of liquid steel during AOD tapping. The types of inclusion at LF end stage are the same as that at LF arrival stage. The compositions of the newly formed inclusions which are originated from reoxidation of liquid steel during LF refining are consistent with the compositions of the newly formed inclusions at LF arrival stage. The mass fractions of SiO 2 in the CaO–SiO 2 –MgO–Al 2 O 3 –CaF 2 inclusions in liquid steel with 0.0100 and 0.0320 mass% Al decrease from 27.7 and 13.1 mass% before AOD tapping to 14.1 and 5.4 mass% at LF arrival stage, respectively. The inclusions in the forged bar are MgO·Al 2 O 3 spinel precipitated from liquid steel during its cooling and dual‐phased spinel + CaOSiO 2 with minor amount of MgO and Al 2 O 3 inclusions formed through the crystallization of CaO–SiO 2 –MgO–Al 2 O 3 inclusions during liquid steel cooling.