Abnormal reduction in work-hardening rate of Cr4Mo4Ni4V martensitic steel induced by interface carbides suppressing boundary sliding

Lath martensitic steels are widely used for their excellent mechanical properties. In this study, we aim to understand how microstructural features affect plastic deformation mechanisms and mechanical responses. While second-phase particles such as carbides are generally believed to enhance strength and work hardening through dislocation obstruction, we found that film-like carbides distributed along substructure boundaries suppress boundary sliding and result in an unusual mechanical response: increased yield strength but decreased tensile strength and work hardening rate. This deviation from conventional expectations is attributed to a shift in deformation mechanism. When boundary sliding is suppressed by the presence of film-like carbides, deformation is dominated by dislocation slip within laths. However, the lack of interfacial plasticity leads to stress localization and dislocation accumulation, limiting further hardening. These findings reveal a distinct mechanism–property correlation in lath martensite and suggest a new approach to tailoring mechanical behavior through interfacial design.