Strengthening and toughening mechanism of medium-Mn austenite steel with staged TRIP and pre-strain control

The microstructure evolution, reversed austenite stability, and fracture mechanism were studied in the multiphase austenite steel (Fe-0.2C–12Mn–3Al-2.0Cu-3.0Ni, wt.%) with the pre-strain control, targeting an improved strength–ductility synergy. The two-step intercritical annealing and pre-strain control effectively improves austenite stability, increases dislocation density, refines grain structure, and increases martensite fraction, and then leading to simultaneous enhancements in ultimate tensile strength (UTS) and total elongation (TEL). The 10% pre-strain control results in UTS of 1341.4 MPa and uniform TEL of 18.7%. The overall improvements in mechanical properties are attributed primarily to the staged TRIP effect, synergized with dislocation strengthening and grain refinement. The staged transformation from austenite to martensite, strategically triggered by pre-strain control, enables a sustained work hardening capability.