Strain-rate-dependent dislocation-martensite interactions in Fe-Mn-Al-Nb medium manganese steel via discrete dislocation dynamics modeling

• A 3D-discrete dislocation dynamics model is developed for dislocation-martensite interactions. • Higher strain rates enhance yield strength via dislocation density and cell structure formation. • Smaller dislocation-martensite spacing increases critical stress for accumulation and release. • Martensite activates multiple slips at 45° orientation for maximum strength. Medium manganese steels (MMnS) exhibit exceptional strength-ductility synergy due to the well-known transformation induced plasticity (TRIP) effects, making it a prime candidate for automotive lightweighting and safety–critical structures. However, the strain-rate-dependent dislocation-martensite interactions governing its strain hardening and plasticity remain incompletely understood, particularly regarding dynamic loading conditions. To address this gap, this study employs an integrated experimental-computational approach by combining dynamic tensile tests (1000–3000 s −1 ) via split Hopkinson bar apparatus, microstructural characterization, and a novel 3D discrete dislocation dynamics (DDD) model simulating dislocation evolution in austenite–martensite systems. Key findings demonstrate that elevated strain rates enhance yield strength by 12.7 %, primarily through intensified dislocation density and dislocation cell formation, though this concurrently exacerbates strain localization. Furthermore, closer dislocation-martensite proximity (300–1200 nm) significantly increases the critical stress required for dislocation accumulation ahead of martensite. Notably, successful bypassing triggers abrupt macroscopic stress drops followed by rapid dislocation proliferation. Critically, martensite promotes dislocation accumulation and induces secondary hardening; its 45° orientation activates distinct slip systems that accumulate higher dislocation densities, yielding the maximum strength. These insights elucidate dislocation-mediated strengthening under dynamic loading, establishing a microstructure-guided framework for designing advanced high-performance steels.