Design of high strength medium manganese zinc coated steel for the automotive industry

The demand for reduced fuel consumption, lower CO₂ emissions, and improved vehicle safety is driving the development of advanced high-strength steels (AHSS). Hot stamping of coated C-Mn-B steels dominates automotive applications due to its ability to produce ultrahigh-strength components. However, these steels exhibit poor elongation, limited crash energy absorption, and require Al-Si coatings with inadequate corrosion resistance. Medium manganese steels (3–12 wt.% Mn), a key material in 3rd generation AHSS, offer superior mechanical properties, lower transformation temperatures, and compatibility with Zn coatings, making them a promising alternative for warm stamping applications. In this study, new Zn-coated medium manganese steels were developed with the following objectives: a) Achieving total elongation (TE) ≥ 10% and ultimate tensile strength (UTS) ≥ 1500 MPa for intrusion-resistant components.b) Achieving TE ≥ 18% and UTS ≥ 1200 MPa (UTS × TE ≥ 21 GPa%) for energy-absorbing components. The alloy system consisted of varying amounts of C, Mn, Al, Cr and B. A total of 72 different variants were identified and analyzed using thermodynamic simulations to evaluate phase volume fractions and chemical compositions. Nine alloys were selected for experimental validation, based on the results of the phase transformation characteristics from the thermodynamic simulations. These alloys were prepared at a laboratory scale, subjected to hot and cold rolling, and subsequently processed through annealing and hot press forming. Based on quasi-static tensile testing, two alloys were identified as promising candidates for pilot scale experiments simulating the industrial heat treatment procedure. This research is partially funded by the European Union under the: --RFCS project WarP – Grant Nº 101112425.& Horizon 2020 research and innovation program, MarieSklodowska-Curie grant agreement No 101146720