Effects of Vanadium Content and Tempering Time on Carbide (Mo, V)C Coarsening Kinetics of Cr‐Mo‐V Steel for Brake Disc

To reduce the carbides coarsening rate and the size during heating processes of the steel for brake discs, different vanadium content is added to the steels for brake discs. In this work, the effect of vanadium content on the coarsening of (Mo, V)C carbide during tempering process was investigated based on transmission electron microscopy (TEM) and first‐principles calculations. The result shows that V 8 C 7 existed before the quenching process of the tested steels, while (Mo, V)C, M 23 C 6 , and M 7 C 3 precipitated during tempering process. After tempering for 1 h, the Mo/(Mo+V) ratio in (Mo, V)C decreased with increasing V content in the tested steels. As the change in Mo content in (Mo, V) C led to the change of interface energy of (Mo, V) C/α–Fe, the interfacial energy of (Mo, V)C/α‐Fe was obtained by first‐principles calculations. As the V content in the tested steels increased from 0.13% to 0.34%, the interfacial energy values of (Mo, V)C/α‐Fe decreased from 0.59 to 0.54 J·m −2 after tempering for 1 h. During the tempering time of 8–24 h, the interfacial energy was the primary factor governing the coarsening rate in the tested steels. Increasing V content in steel could inhibit coarsening of (Mo, V)C by reducing the Mo/V ratio in (Mo, V)C and decreasing the interfacial energy.).