Compressive Behavior of an Fe-Mn-Al-Mo-C Lightweight Steel at Different Strain Rates

Compression tests over a wide range of strain rates were performed on cold-rolled and annealed, as well as annealed-and-aged, Fe-26Mn-8Al-1.2C-3Mo steel to elucidate the roles of Mo₂C precipitation and κ/Mo₂C co-precipitation in microstructural evolution and compressive behavior. The annealed microstructure consists of partially deformed and equiaxed ultrafine recrystallized austenite grains, with Mo₂C carbides uniformly dispersed throughout the matrix. Aging at 550 °C induces nanoscale spherical κ carbides, while the size and spacing of Mo₂C particles remain essentially unchanged. Both conditions exhibit pronounced strain-rate strengthening, primarily attributed to intensified dislocation–carbide interactions. In the annealed state, deformation is dominated by dislocation bypassing of Mo₂C carbides, resulting in discontinuous slip microbands. After aging, κ-carbide precipitation facilitates slip-band propagation and promotes interactions among adjacent slip bands. As the strain rate increases from 10⁻³ to 10⁰ s⁻¹, dislocation density increases, slip-band propagation is hindered, and the strain-hardening rate decreases. At 10³ s⁻¹, adiabatic thermal softening becomes significant, leading to a further reduction in strain hardening. Overall, aging increases strength but reduces strain-rate sensitivity in the low strain-rate regime due to κ-carbide-induced slip-plane softening and an increased effective slip distance.