Microstructure evolution and mechanical properties of the lightweight Fe-28Mn-8Al-1C steel under rolling at room and cryogenic temperatures

A lightweight Fe-28Mn-8Al-1C steel was rolled at room temperature and the liquid nitrogen temperature. The effect of the deformation temperature on the microstructures and mechanical properties of the lightweight steel was systematically studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), microhardness and tensile testing. The results showed that both cryogenic rolling(CR) and room temperature rolling(RTR) significantly refined the microstructure of the steel to the nanometer level, and CR achieved a finer grain size and a higher dislocation density. The plastic deformation mechanism of lightweight steel was dominated by dislocation slips during the process of rolling, but CR also led to the occurrence of deformation twinning. The lightweight steel formed a Copper {112}(111) texture under low strain, which transformed into a Brass {110} (112) texture under high strain. The transformation process was accelerated by CR, and a more intense Brass {110} <112> texture was obtained. Under the same level of reduction, increase in the intensity of the strength caused by CR was significantly greater than that of RTR. Due to the generation of deformation twins in the process of CR, the samples subjected to CR showed greater elongation, and the corresponding fracture morphology transferred from ductile fractures in the undeformed state to ductile-brittle mixed fractures after a 90% deformation.