Effect of bismuth on the microstructural evolution and properties of single-crystal Fe during rolling: a molecular dynamics study

Bi-containing free-cutting steel has consistently attracted attention in the field of materials processing. The molecular dynamics (MD) simulations were used to investigate the impact of bismuth (Bi) nanoparticles on the internal structural evolution and mechanical properties of single-crystal Fe during the rolling process. The influence of varying rolling depths in the presence of nanoparticles is also examined. The results indicate that Bi nanoparticles significantly affect rolling force, stress distribution, and the generation and propagation of dislocations during nano-rolling. The deformation of Bi particles reduces both the rolling force and the overall von Mises stress in the Bi-affected region, while simultaneously hindering the generation and movement of dislocations, resulting in localized strengthening. As the rolling depth increases, the total rolling force, friction coefficient, and von Mises stress gradually rise. However, in the Bi particle region, the structural changes of Bi particles with increasing rolling depth lead to variable effects on normal rolling force, tangential friction force, and friction coefficient.

The free-cutting alloy model was constructed using the molecular/atomic simulation software Atomsk. The entire simulation process was conducted using MD on the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) platform, with interatomic interactions described by classical force fields. The MD simulation time step was set to 1 fs, and the temperature was maintained constant via the Nose–Hoover thermostat. Data post-processing and analysis were performed using the OVITO software.