Compressive behavior of a Fe–Mn–Al–C lightweight steel at different strain rates

Experiments were conducted to evaluate the compression behavior at strain rates in the range 10⁻³–10³ s⁻¹ of a Fe–Mn–Al–C lightweight steel micro-alloyed with Mo and Nb after aging at different temperatures. The results show that the microstructures of the steels after aging at temperatures from 400 to 600 °C are composed of austenite grains and two types of nano-sized precipitates, (Nb,Mo)C and κ-carbides, distributed uniformly in the matrix. Increasing the aging temperature results in the growth of the κ-carbides but has no effect on the sizes and distribution of the (Nb,Mo)C particles. The aged steel exhibits a significant strain-rate strengthening effect resulting from the enhancement of the interactions between dislocations and the carbides in the matrix at higher strain rates. With increasing strain rate, the strain hardening rate decreases because more κ-carbides are sheared by dislocations during deformation at higher strain rates, which causes a reduction in the hindrance to dislocation slip. Increasing the aging temperature leads to an increase in the strength for the same strain rate, and an enhancement in the strain-rate sensitivity of the yield strength at strain rates of 10⁻³–10⁰ s⁻¹ due to the increasing precipitation of κ-carbides. In addition, the effect of dynamic strain aging during deformation on the strain hardening rate was discussed as well.