Multiscale experimental and numerical investigations of deformation and failure in martensitic steels

Profoundly comprehending the mechanical degradation behavior in martensitic steels is of paramount significance for the safety and integrity of industrial tooling applications. Deformation and failure are inherently multiscale phenomena, governed by intrinsic and extrinsic factors. As temperature decreases, the ductile-brittle transition (DBT) occurs. Through multiscale experimental characterization, this study unravels the dominant mechanisms behind DBT by analyzing fracture angle, dimple fraction, and dislocation activity, highlighting that the transition is dependent on stress state but almost independent of strain rate. A robust parameter identification scheme for the phenomenological crystal plasticity (CP) model is developed to numerically capture the temperature-sensitive and rate-insensitive nature of the materials. Based on the fine-tuned Kurdjumov-Sachs (K-S) relation, virtual polycrystalline aggregates are constructed, fully accounting for hierarchical microstructural features. We introduce a top-down macro-microscale modeling framework to systematically characterize the effects of temperature and stress state on deformation and failure properties by integrating modified Bai-Wierzbicki (MBW) damage mechanics with CP simulations via displacement mapping. The lattice reorientation behaviors responsible for macro-mechanical responses are elucidated. By manipulating initial prior austenite grain (PAG) orientations, the study also delves into the effects of PAG orientation on the deformation behaviors of child martensite, demonstrating that cube-orientated PAGs may induce small lattice rotation, uniform deformation and enhanced strain hardening in martensite under plane strain tension loading. These multiscale experimental and numerical investigations provide fundamental insights into deformation and failure in martensitic steels and will guide strategies for material design and engineering applications.