Thermo-viscoelastic mechanical behavior and fractography analysis of lean duplex stainless steel SUS821L1

• Flow stress in both quasi-static and dynamic tests for lean duplex stainless are conducted in low temperature • Dynamic tensile test is conducted using a vertical split Hopkinson tensile bar with a novel cooling chamber. • The effect of strain-induced martensitic transformation are observed • A modified Johnson-Cook model, incorporating strain rate and temperature coupling, better represents the material's behavior than the original model. This study examines the tensile behavior of lean duplex stainless steel SUS821L1, a low-nickel alloy with potential for structural applications. Quasi-static and dynamic tensile tests are conducted over a temperature range of 233–293 K. Dynamic tests use a vertical split-Hopkinson tensile bar (SHTB) equipped with a novel cooling chamber to maintain low temperatures. Flow stress increases with decreasing temperature under both loading regimes, with greater temperature sensitivity observed in quasi-static conditions. Strain rate sensitivity is more pronounced at low strain levels, while reduces at higher strains due to strain-induced martensitic transformation in quasi-static reduces the flow stress gap between loading modes. Specific energy absorption (SEA) decreases with temperature in dynamic tests, reflecting reduced elongation. In quasi-static conditions, SEA increases from 293 K to 273 K, then declines at lower temperatures, consistent with changes in elongation. Fractography supports these trends: large dimples at 293 K indicate ductility, while mixed dimples at 273 K suggest enhanced phase heterogeneity and delayed necking. Below 273 K, fine dimples dominate, linked to increased strain-induced martensitic transformation and reduced ductility. Dynamic fractures show shallow, serrated features and fine dimples with limited temperature sensitivity, indicating suppressed transformation due to adiabatic heating. Furthermore, a modified Johnson–Cook model incorporating coupled strain rate and temperature effects shows improved agreement with experimental results, particularly under dynamic loading.