Investigation of the Dissolution Behavior of AlN in CaO–Al2O3–MgO Refining Slag and CaO–Al2O3–F–Li2O–BaO Mold Flux

Abstract

Low-density steels have garnered widespread attention as novel lightweight materials. Owing to its high Mn and Al content, brittle AlN inclusions, detrimental to both steelmaking and steel properties, can precipitate directly from the molten steel. Employing slag absorption effectively removes these floating AlN inclusions from the molten steel. Herein, a series of analytical methods are utilized to investigate the dissolution behavior of AlN in CaO–Al₂O₃–MgO refining slag and CaO–Al₂O₃–F–Li₂O–BaO mold flux. The results indicate that the initial dissolution temperatures of AlN in the slag and mold flux are 1361 and 1080 °C, respectively. The dissolution in the refining slag is attributed to the high-temperature self-decomposition of AlN, producing N_2(g). In the mold flux, the dissolution reaction involves both the high-temperature self-decomposition of AlN and its reaction with Li₂O in mold flux, generating N_2(g) and Li_(g). No reaction interface is observed at the AlN-slag/mold flux boundary. As the dissolution mass of AlN in the slag/mold flux increases, the Al₂O₃ content in the slag/mold flux rises. The main phases in slag transition from Ca₉(Al₆O₁₈) to Ca₁₂Al₁₄O₃₃ and Ca₃Al₂O₆. In the mold flux, the LiBaF₃ phase disappears, and the 11CaO·7Al₂O₃·CaF₂ phase, which can degrade the flux's physicochemical properties, becomes the dominant phase.