Uncovering Microstructure–Property Relationship in Ni-Alloyed Fe–Mn–Al–C Low-Density Steel Treated by Hot-Rolling and Air-Cooling Process

This paper focuses on the relationship between the microstructure and tensile properties of Fe–Mn–Al–C low-density high-strength steel processes by hot-rolling and air-cooling process. The microstructure analysis reveals that the combination of hot-rolling and air-cooling results in the formation of heterogeneous structures comprising different-sized γ and B2 phases in the low-density steel with the addition of nickel (Ni). The addition of Ni promotes the formation of the B2 phase and induces the pinning of B2 phase particles at the γ grain boundaries. This pinning effect effectively hinders the growth of the γ grains, leading to grain refinement. The tensile test results demonstrate that LDS-5Ni (low-density steel, LDS) exhibits excellent high strength and ductility combination, e.g., a tensile strength of 1535 MPa, yield strength of 1482 MPa, and elongation of 23.3%. These remarkable mechanical properties are primarily attributed to the combined strengthening contributions of grain refinement and duplex nano-sized second-phase precipitation hardening.