Characteristics and formation mechanism of MgO-enriched inclusions in 2507 super duplex stainless steel during LF refinement

Abstract

Herein, we present the formation mechanism and characteristics of MgO-enriched inclusions in 2507 super duplex stainless steel (SDSS) during the ladle furnace (LF) refining process using a combination of thermodynamic calculations and experimental approach. The compositional analysis reveals that two types of inclusions exist in 2507 SDSS after aluminum (Al) de-oxidation during LF refining process, i.e., CaO-SiO2-Al2O3-MgO and Al2O3-MgO inclusions. Furthermore, the inclusions are transformed into CaO-(SiO2)-Al2O3-MgO inclusions after calcium (Ca) treatment. In addition, the presence of [Mg] lowers the CaO and Al2O3 content of CaO-(SiO2)-Al2O3-MgO, forming MgO-enriched multi-component inclusions. Thermodynamic analysis confirms that the reaction of [Mg] with CaO and Al2O3 can occur in the temperature range of 1500 to 1600 °C during the LF refining process, however, the reaction between [Mg] and SiO2 is thermodynamically not feasible. Overall, the current study demonstrates that more attention should be paid to the MgO-enrichment of inclusions during LF refinement of SSDS.