Molecular Dynamics Study on the Effect of Nb for the Carbon Segregation Behavior Under High Temperature

Nb can effectively enhance the strength of steel through precipitation strengthening. However, the micro-scale effects of Nb in steel, especially the atomic-scale mechanisms at high temperatures, have been rarely studied. In this study, we established Fe–C and Fe–C–Nb system models using LAMMPS to explore the effects of Nb at high temperatures (1050 °C to 1200 °C) and to provide theoretical insights for the design of Nb-containing high-strength steels. The results demonstrated that Nb can significantly increase the kinetic energy of C and Fe atoms at high temperatures. In addition to the significant increase in the diffusion coefficient of atoms, the grain size also increased at the corresponding temperature, and the upper temperature limit of the segregated clusters formation was reduced. The atomic clusters formed in the simulated system were primarily composed of C atoms, with Nb atoms dispersed throughout the system. In comparison to the system without Nb, as the temperature increased, the size of the atomic clusters in the Fe–C–Nb system decreased instead of increased, indicating that Nb inhibited the growth of atomic clusters. Through tracking labeled atoms, it was found that once stable atomic clusters were formed, some atoms within the clusters underwent a cyclic process of escaping, being captured, re-escaping, and being recaptured. Through tracking labeled atoms, it was found that once stable atomic clusters were formed, some atoms within the clusters underwent a cyclic process of escaping, being captured, re-escaping, and being recaptured. Furthermore, atomic exchange occurred between closely approaching clusters. These migration mechanisms of atoms were the fundamental reason for the size stability of the clusters.