Thermodynamic optimization of aluminothermic reduction for Nb-Ti-Fe alloy preparation

In the field of iron and steel materials, Nb-Ti composite microalloying technology has become a core method to improve the strength and toughness of steel materials. Nb-Ti-Fe alloy was prepared by aluminothermic reduction of Nb-rich slag with Bayan Obo niobium concentrate as raw material, which can alleviate China's high dependence on imported ferroniobium alloys. Investigating the reduction mechanism and distribution behavior of Nb and Ti during the process is crucial for efficient resource utilization. Exploring the reduction mechanism and distribution behavior of Nb and Ti in the reduction process is an essential prerequisite for efficient resource utilization. In this study, FactSage thermodynamic calculations were combined with experimental investigation to systematically analyze the effects of Al addition amount, reaction temperature, binary basicity w(CaO)/w(SiO₂), and SiO₂ content in the slag system on alloy composition, microstructure, and mineral phase of the final slag. Thermodynamic optimization and experimental verification show that when the Al addition amount(mass fraction) is 12.39%, the heat released by aluminothermic reduction increases the system temperature by 200-300 ℃, and the reaction can be carried out steadily above 1 800 ℃.When the basicity R is 1.0 with CaF₂ addition, the molten slag presents good fluidity and the optimal slag-metal separation effect is achieved. Thermodynamic calculations confirm that reducing the mass fraction of SiO₂ in slag to 20% eliminates the pure Si phase (CRSI) in the alloy and increases the contents of Nb and Ti, thus improving the overall quality of the alloy. The final slag mainly consists of CaAl₂Si₂O₈ phase, the high-melting-point Al₂O₃ phase, and CaTiO₃ phase. The increase of slag viscosity is confirmed as the key factor leading to entrainment loss of niobium-titanium alloy particles (MAPs). This research provides a thermodynamic basis and experimental support for the process optimization of preparing Nb-Ti-Fe alloy by aluminothermic reduction of Nb-rich slag.