Regular Article

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

¹ Hongxing Iron & Steel Co. Ltd., Jiuquan Iron and Steel Group Corporation, Jiayuguan 735100, Gansu, China
² State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing, China

^* e-mail: chenxingrun850204@126.com

Received: 23 May 2022
Accepted: 28 July 2022

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.