Phase equilibria in the CaO‒Al2O3‒TiN system and CaO‒Al2O3‒Ti2O3‒TiN system at 1500°C

Abstract

Nitride inclusions such as TiN and AlN often appear in the smelting process of aluminum‒titanium alloy steel. The phase diagram of nitrogen-containing slag system is crucial for guiding the design of the denitrification slag system. In the present work, the high-temperature equilibration-quench experiment was employed, and the types and compositions of equilibrium phases were identified by electron probe micro analysis and X-ray diffraction. The 1500°C isothermal section of CaO‒Al₂O₃‒TiN system and the 1500°C isothermal space phase diagram of CaO‒Al₂O₃‒Ti₂O₃‒TiN system in specific compositional ranges were constructed for the first time. Among them, the isothermal section of CaO‒Al₂O₃‒TiN system includes six three-phase fields, one two-phase field, and a single liquid phase field; the isothermal space phase diagram of CaO‒Al₂O₃‒Ti₂O₃‒TiN system includes four four-phase fields, six three-phase fields, six two-phase fields, and a single liquid phase field. By comparison, it can be found that the CaO‒Al₂O₃‒Ti₂O₃ slag system has a higher equilibrium solubility of nitride than that of the CaO‒Al₂O₃ slag system. In addition, the dissolution type and the equilibrium solubility of nitride inclusions (AlN and TiN) in slag were analyzed and discussed using the experimental phase diagram of CaO‒Al₂O₃‒Ti₂O₃‒TiN system.