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The effect of Al content on the hot deformation behavior of high-Mn low density Fe-Mn-Al-C steels was investigated by the 3D processing map at the temperatures of 850-1050 °C and the strain rates of 0.001-10s-1. The high-Al steel showed a higher flow stress and a greater activation energy (443 kJ/mol) in contrast to the low-Al steel (394 kJ/mol). The microstructures of 8Al steel and 10Al steel depends on the deformation parameters. The initial hot rolling microstructure has been displaced by the recrystallized structure and substructures for both steels, while the unstable zone has deformation bands and flow localization. As the Z content increases with increasing Al content, this leads to a significant inhibition of the DRX process, resulting in an unstable domain with deformation zones and flow localization. For high-Al steel, the morphology and distribution of ferrite transform from the continuous band ferrite to discontinuous granular ferrite, moreover, the flow localization features cannot be observed with the decrease of strain rate to 0.001s-1. Furthermore, the proportion of instability region for each of the strains increases with the increasing of the Al content, the high Al content weakens the workability of the Fe-Mn-Al-C steels.

In the present work, two Fe-18Mn-10Al-xC low-density steels with different C concentrations were investigated. It is revealed that the difference in C concentration resulted in a marked difference in the microstructures of the investigated steels. The microstructure consisted of ferrite and austenite as well as of precipitates in Fe-18Mn-10Al-0.8C (0.8C steel); while carbides distributed on the austenite matrix in Fe-18Mn-10Al-1.2C (1.2C steel) after the same heat treatment. During deformation, dislocations exhibited a typical paired superdislocation feature in ferrite in 0.8C steel, extensive planar glide occurred in austenite in both steels and Taylor lattice-like structures, and well-developed microbands appeared in 1.2C steel. Overall, 0.8C steel demonstrated a tensile strength of 973.6 MPa and elongation of 44%, and 1.2C steel received a lower tensile strength (881.3 MPa) and a much higher elongation (78%). The strain hardening behavior of the two alloys was also different. The strain hardening rate decreased with strain in a non-monotonic feature for 0.8C steel, while it exhibited a moderate inflection in 1.2C steel.

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