Exploring changes in the tensile properties of Fe–30Mn–8Al-1.3C (wt%) lightweight steel at 298 K and 77 K with the chemical decomposition degree

This study investigated the deformation behavior and unexpected brittle fracture of Fe-30Mn-8Al-1.3C (wt%) steel under various aging conditions (for 3 min–2 hr) and tensile temperatures (298 K and 77 K). The initial microstructures of all non-aged and aged specimens showed a single fcc matrix without κ -carbides. Despite the high stacking fault energy (SFE), tensile deformation occurred primarily through planar dislocation slip across all aging and tensile conditions due to the high friction stress caused by solute atoms, with no evidence of mechanical twinning or strain-induced phase transformation. The change in the yield strength (YS) with aging time and tensile temperature was explained by contributions of friction stress and solid-solution hardening, except for the non-aged specimen with a higher YS value owing to its extremely high vacancy concentration. To elucidate the effects of aging and tensile conditions on the ultimate tensile elongation and uniform elongation of the present steel, the variation in the Taylor lattice domain sizes was employed. At 77 K, unexpected brittle fracture was observed in specimens aged for 40 min-1 hr. This phenomenon was attributed to the interaction between the ordered structure induced by chemical decomposition and stacking faults in the solute-lean γ ʹ phase. As aging time increased, reductions in Al and C concentrations lowered the SFE of the γ ʹ phase, promoting dislocation separation into partials under high stresses at 77 K. The repulsive interactions between Al and C atoms within stacking fault regions caused widespread lattice instability, resulting in immediate fracture after yielding.