Thermodynamic analysis of the Fe-Mo-B ternary system

Thermodynamic analysis of the Fe-Mo-B ternary system was performed using the CALPAHD approach coupled with the first-principles calculation, and effect of Mo addition in steels on the grain boundary segregation tendency of B was discussed by means of the grain boundary phase model. The calculated phase diagrams and thermodynamic properties well reproduced the experimental data as well as the results of the first-principles computation, and thus the parameter set with high accuracy for this ternary system was evaluated. Grain boundary segregation behavior of B and Mo was analyzed by means of the parallel tangent scheme. The Gibbs energy of the liquid phase obtained in the present work was adopted for that of the grain boundary phase. According to the model, the amount of segregated B in grain boundaries decreased with descending temperature. This phenomenon is due to the formation of boride phases such as Fe₂B and τ₂ phases in the iron matrix.