-manganese steels are seen as a strong contender for the 3rd generation of Advanced High Strength Steels (AHSS) for automotive applications, primarily due to its excellent strength-ductility combination and affordable cost of production. Recent research indicates that the intriguing mechanical properties of these steels are linked to the stacking fault energy and the stability of the retained austenite. To further enhance their mechanical properties, the alloy chemistry and microstructure need to be suitably designed. In this work, we developed new grades of medium-manganese steel and established the optimum thermomechanical processing routes with the aid of physical metallurgy principles and computational alloy thermodynamics based on the CALPHAD approach. The evaluation of mechanical properties show that the steel developed in the present study have excellent mechanical properties with a high value for the product of tensile strength and uniform elongation (>35,000 MPa%). Detailed characterization using SEM-EBSD was performed to understand the strain hardening behavior, with particular attention to the effects of TRIP (Transformation-Induced Plasticity) and TWIP (Twinning-Induced Plasticity) mechanisms. In-situ synchrotron studies were also carried out to analyze strain partitioning among individual phases and its influence on the serrated plastic flow under different strain rates. Additionally, the impact of dynamic loading at high strain rates on the plastic deformation behavior and microstructural evolution was examined. The results highlight the major influence of strain rate on retained austenite stability and detailed investigations further explore the role of adiabatic heating, which becomes a prominent factor at higher strain rates.

This comprehensive study provides valuable insights into the compositional design and thermo-mechanical processing of medium manganese steels, combining computational and experimental approaches. The findings underscore the effectiveness of a systematic approach, as opposed to conventional heuristic methods. The integration of computational modeling and experimental validation enables a more efficient and targeted approach, enhancing the understanding and optimization of steel properties. The study emphasizes the potential for a more rational and informed design process in the field of medium manganese steels.