Phase equilibria in the CaO‒Al ₂ O ₃ ‒TiN system and CaO‒Al ₂ O ₃ ‒Ti ₂ O ₃ ‒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‒Al 2 O 3 ‒TiN system and the 1500°C isothermal space phase diagram of CaO‒Al 2 O 3 ‒Ti 2 O 3 ‒TiN system in specific compositional ranges were constructed for the first time. Among them, the isothermal section of CaO‒Al 2 O 3 ‒TiN system includes six three‐phase fields, one two‐phase field, and a single liquid phase field; the isothermal space phase diagram of CaO‒Al 2 O 3 ‒Ti 2 O 3 ‒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‒Al 2 O 3 ‒Ti 2 O 3 slag system has a higher equilibrium solubility of nitride than that of the CaO‒Al 2 O 3 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‒Al 2 O 3 ‒Ti 2 O 3 ‒TiN system.