Mechanical Performance and Strain-Hardening Behavior of a Sustainable Fe-C-Ni-Mo(-Si) Advanced High Strength Steel

The automotive industry increasingly demands sustainable advanced high-strength steels (AHSS). In this study, The Fe-C-Ni-Mo(-Si) sustainable AHSS is developed combined with three simplified and industrially feasible heat-treatment routes. Tensile testing, together with Bouaziz law and complementary Hollomon and modified C–J descriptions, is used to map strain-hardening behavior and deformation mechanisms. The steels exhibit ultimate tensile strengths ranging from 546 to 1347 MPa, with a maximum UTS×T.El of 27.58 GPa·%, exceeding GEN1 and meeting GEN3 performance targets. One investigated condition achieves GEN3-level performance index (P.I. = 359.78 MPa), combining high strength with exceptional global formability. The P1 route prioritizes ultrahigh strength through ferrite–martensite microstructures, whereas the P2 and P3 routes exploit multiphase synergy to enhance ductility and formability. Retained austenite with appropriate mechanical stability (Md ≈ 250 °C) and stacking fault energy (∼20 mJ m -2 ) enables sustained strain hardening via the TRIP effect, leading to total elongations up to 41.11%. Overall, this work validates the Fe-C-Ni-Mo(-Si) steel as a sustainable AHSS that achieves GEN3-level performance through process regulation, offering a viable pathway toward sustainable GEN3 AHSS.