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One of the ways to obtain high-quality products and meet ever-increasing requirements on properties of steel is microalloying it with rare earth elements such as cerium. Cerium can significantly affect mechanical properties of steel even at low concentrations. To reduce the cost of steel, it is rational to add cerium into steel not with ferroalloys but by direct reduction from oxide systems. In order to study this process, thermodynamic modeling of the reduction of cerium from slags of the CaO–SiO₂–Ce₂O₃ system, containing 15% Al₂O₃ and 8% MgO, with aluminum and calcium carbide at temperatures of 1 550 and 1 650°C is carried out. The simulation is performed using the HSC 6.12 Chemistry software package (Outokumpu) based on Gibbs energy minimization and using the simplex planning lattice method. The results of thermodynamic modeling are presented in the form of composition-property (equilibrium cerium content in the metal) diagrams for temperatures of 1 550 and 1 650°С. When using metallic aluminum as a reducing agent, increasing the basicity of the slag (CaO/SiO₂) from 2 to 5 at a temperature of 1 550°C leads to an increase in the equilibrium cerium content in the metal from 2 to 20 ppm in the concentration range of 0–15٪ Ce₂O₃, i.e. an increase in the basicity of the slag is beneficial for the development of the cerium reduction process. An metal temperature increase also has a positive effect on the process of reduction of cerium with aluminum. With an increase in temperature to 1 650°С, the equilibrium content of cerium in the metal increases from 4 ppm to 30 ppm in the concentration range of 0–15٪ Ce₂O₃. The use of calcium carbide as a reducing agent leads to an increase in the concentration of cerium in the metal to 30 and 40 ppm at temperatures of 1 550 and 1 650°C, respectively, at a basicity of 5. The decisive role of slag basicity, cerium oxide concentration and temperature in the development of the process of cerium reduction with aluminum and calcium carbide is confirmed.