Achieving High Specific Strength via Multiple Strengthening Mechanisms in an Fe-Mn-Al-C-Ni-Cr Lightweight Steel

The development of lightweight steels with high specific strength is critical for automotive applications and energy savings. This study aimed to develop a high-performance lightweight steel with high specific strength by designing an alloy composition and optimizing thermomechanical processing. A novel Fe-28.6Mn-10.2Al-1.1C-3.2Ni-3.9Cr (wt.%) steel was investigated, focusing on microstructural evolution, mechanical properties, and strengthening mechanisms. The steel was processed through hot-rolling, solution treatment, cold-rolling, and subsequent annealing. Microstructural characterization revealed a dual-phase matrix of austenite and ferrite (6.8 vol.%), with B2 precipitates distributed at the grain boundaries and within the austenite matrix, alongside nanoscale κ-carbides (<10 nm). Short-time annealing resulted in the finer austenite grains (~1.1 μm) and the higher volume fraction (5.0%) of intragranular B2 precipitates with a smaller size (~0.18 μm), while long-time annealing promoted the coarsening of austenite grains (~1.6 μm) and the growth of intergranular B2 particles (~0.9 μm). This steel achieved yield strengths of 1130~1218 MPa and tensile strengths of 1360~1397 MPa through multiple strengthening mechanisms, including solid solution strengthening, grain boundary strengthening, dislocation strengthening, and precipitation strengthening.