Abstract：Martensite-ferrite dual-phase (DP) steel is widely utilized in industry owing to its excellent combination of mechanical properties; however, its microscopic deformation mechanisms remain incompletely understood. To elucidate these mechanisms, this study employs three-dimensional discrete dislocation dynamics (3D-DDD) simulations based on a generalized misorientation-dependent dislocation–grain boundary interaction model. By systematically varying dislocation densities, grain sizes, and interface characteristics, we simulated the mechanical responses and microstructural deformation behaviors of single-phase martensite, single-phase ferrite, and martensite–ferrite dual-phase structures under uniaxial tensile loading. The results show that the elongated grain structure in martensite significantly impedes dislocation motion, resulting in a lower plastic strain accumulation rate and strongly suppressed transgranular dislocation activity. In contrast, ferrite exhibits frequent transgranular dislocation glide and pronounced plastic relaxation. The martensite–ferrite dual-phase structure demonstrates a remarkable synergistic strengthening effect, which is further enhanced by the accumulation of geometrically necessary dislocations (GNDs) at the martensite–ferrite interfaces. This study clarifies the synergistic deformation mechanisms in martensite–ferrite DP steel at the microscale and provides an important theoretical basis for the microstructure-based design of dual-phase steels.
2026, Vol. 47 
