Evolution of (Ti, Mo)C particles in austenite of a Ti–Mo-bearing steel

Highlights: • We study the evolution of titanium–molybdenum carbide particle in austenite. • Molybdenum-enriched region formed near the outer layer of particle. • Coarsening is controlled by the transport of titanium atoms through the layer. • Growth is accompanied by shape change from spherical to polyhedral, and to irregular. The present work investigated the evolution of (Ti, Mo)C particles in austenite of a Ti-Mo-bearing steel during isothermal holding after hot deformation at 925 °C. Results show that the (Ti, Mo)C particles sequentially undergo dislocation-assisted diffusion controlled growth stage, interface-reaction controlled slow coarsening stage, and bulk diffusion controlled fast coarsening stage. The Mo-enriched region near the outer layer of the (Ti, Mo)C particles results in the slow coarsening stage. To reduce the total interface and strain energy correlated with austenite matrix, the particle morphology evolution follows spherical → polyhedral → irregular route. Compared to TiC, dispersive refined (Ti, Mo)C particles suppress austenite recovery and recrystallization more effectively, which favors maintaining the deformed microstructures at high temperatures.