The study investigates the microstructural properties of advanced high-strength and supra-ductile TRIP and TWIP steels with high manganese concentrations (15 to 25 mass%) and additions of aluminum and silicon (2 to 4 mass%). The steels exhibit multiple martensitic transformations (γfcc → χhcp → χbcc) in TRIP steel at higher strain rates and ambient temperatures, leading to pronounced strain hardening and high tensile strength (>1000 MPa) with improved elongations to failure (>50%). In contrast, the TWIP steel shows extensive twin formation under deformation below 150°C at low and high strain rates, achieving extremely high tensile ductility (>80%) and energy absorption without brittle fracture. The governing microstructural parameters are the stacking fault energy (Γfcc) of the fcc austenite and the phase stability determined by the Gibbs free energy (ΔG°−ε), which are influenced by manganese content and additions of aluminum and silicon. The stacking fault energy and Gibbs free energy were calculated using the regular solution model, showing that aluminum increases Γfcc and suppresses the γfcc→χhcp transformation, while silicon sustains this transformation and decreases Γfcc. At critical values of Γfcc and ΔG°−ε, twinning is favored, while at lower values, martensitic phase transformation dominates. These steels exhibit excellent ductility and enhanced impact properties, making them suitable for complex deep drawing and stretch forming operations, as well as for crash-absorbing frame structures.The study investigates the microstructural properties of advanced high-strength and supra-ductile TRIP and TWIP steels with high manganese concentrations (15 to 25 mass%) and additions of aluminum and silicon (2 to 4 mass%). The steels exhibit multiple martensitic transformations (γfcc → χhcp → χbcc) in TRIP steel at higher strain rates and ambient temperatures, leading to pronounced strain hardening and high tensile strength (>1000 MPa) with improved elongations to failure (>50%). In contrast, the TWIP steel shows extensive twin formation under deformation below 150°C at low and high strain rates, achieving extremely high tensile ductility (>80%) and energy absorption without brittle fracture. The governing microstructural parameters are the stacking fault energy (Γfcc) of the fcc austenite and the phase stability determined by the Gibbs free energy (ΔG°−ε), which are influenced by manganese content and additions of aluminum and silicon. The stacking fault energy and Gibbs free energy were calculated using the regular solution model, showing that aluminum increases Γfcc and suppresses the γfcc→χhcp transformation, while silicon sustains this transformation and decreases Γfcc. At critical values of Γfcc and ΔG°−ε, twinning is favored, while at lower values, martensitic phase transformation dominates. These steels exhibit excellent ductility and enhanced impact properties, making them suitable for complex deep drawing and stretch forming operations, as well as for crash-absorbing frame structures.