Simultaneous improvement of strength and ductility in Fe–Mn–Al–C steel realized by cold rolling plus aging treatment

In the Fe–Mn–Al–C low-density steels, aging treatment is generally employed to strengthen the steels through the formation of κ-carbides, which however results in a reduced strain-hardening rate and ductility due to the shearable nature of the κ-carbides. Here, we report an aging-induced unprecedented improvement in both the strength and ductility of a cold-rolled Fe–Mn–Al–C steel. Specifically, the aging treatment at 550 °C for 10 h results in an increment in ultimate tensile strength from 1176 MPa to 1251 MPa and uniform elongation from 5.00 % to 12.11 % compared to the cold-rolled specimen at 30 % rolling reduction. Microstructural examination revealed that the aging treatment resulted in preferential precipitation of κ-carbides within the existing dislocation structures formed during cold-rolling. The pinning effect of the κ-carbides suppressed the activity of dislocation cross-slip and prevented the further development of these dislocation structures that could lead to the local strain softening. Moreover, new slip bands were generated owing to the shearing of κ-carbides, stimulating the activation of dislocation planar slip. These combined mechanisms enhanced the dislocation storage capacity in cold-rolled specimens, thereby improving both strain-hardening rates and uniform elongation. Additionally, the influence of cold-rolling reduction on the aging-induced variation in the strain-hardening behavior was also explored. This study provides a novel strategy to simultaneously enhance the strength and ductility of the cold-rolled Fe–Mn–Al–C low-density steel by simple aging treatment.