From Plasticity to Fracture in Pearlitic Microstructures: Atomistic Study of Cementite Thickness and Deformation Localization

Pearlitic steels achieve an exceptional balance of strength and ductility through the lamellar stacking of ferrite and cementite. While this synergy enhances mechanical performance, cementite also serves as a preferential site for crack initiation, making its thickness and the extent of deformation localization caused by dislocation pile-ups critical factors in the plasticity–fracture transition. In this study, molecular dynamics simulations were performed to clarify how cementite thickness and dislocation pile-ups govern deformation and fracture. The results reveal that thinner cementite or smaller pile-ups promote dislocation emission across the interface, whereas thicker cementite and larger pile-ups facilitate crack initiation within cementite. Comparison with a conventional continuum model showed qualitative agreement but also highlighted nanoscale effects—such as core relaxation of penetrated dislocations in cementite—that are beyond continuum descriptions. These findings provide atomistic insights into the mechanisms controlling the plasticity–fracture transition in pearlitic microstructures.