Microstructure Evolution and Age-Hardening Behavior of Microalloyed Austenitic Fe-30Mn-9Al-0.9C Light-Weight Steels

The aging behavior and mechanical properties of microalloyed austenitic Fe-30Mn-9Al-0.9C light-weight steels were investigated through transmission electron microscopy analysis, electron backscatter diffraction analysis, tensile tests, and Vickers hardness tests. The base steels were aged at 823 K (550 A degrees C) for up to 10,000 minutes. The true stress-strain responses of solution-treated samples before aging showed that the addition of Nb and/or V improved the strength by grain refinement and precipitation hardening. During the process of tensile deformation, the strain-hardening rate of Fe-30Mn-9Al-0.9C steel steadily increased due to the microband-induced plasticity (MBIP) from the onset of plastic deformation to epsilon = 25 pct, while such behavior was weakened and not observed in Nb- and/or V-added steels despite MBIP. In the early stage of aging, the Vickers hardness gradually increased with an increase in the aging time due to the precipitation of kappa-carbide of (Fe,Mn)(3)AlC and remained stagnant between the aging times of 1000 and 3000 minutes. The hardness increased again after 3000 minutes due to the formation of ferrite and brittle beta-Mn.