Impact toughness of Fe-Mn-Al-C austenitic low-density steel solution treated at different temperatures

The present study explored the impact fracture behavior of a Fe-25Mn-10Al-1.1C austenitic low-density steel solution treated at two temperatures. There are lots of alpha + kappa-carbides distributing along austenite grain boundaries when the steel was solution treated at 800 degrees C (the S8 sample), while there is only austenite with abundant annealing twins in the steel solution treated at 1000 degrees C (the S10 sample). The S8 and S10 samples demonstrate significant difference in the V-notch impact energy, i.e., 16.8 and 67.0 J, respectively. Further instrumental impact tests reveal that this impact energy discrepancy is mainly reflected in the plastic deformation energy and post-brittle fracture energy. The S8 sample exhibits an atypical ductile fracture morphology characterized by dimples, secondary cracks, and flat facets, while the S10 sample exhibits a ductile fracture with well-developed dimples and slip bands. Grain boundary precipitation of alpha + kappa-carbides and the differences in deformation characteristics and the proportion of HAGBs and twins are the main reasons for the difference in the impact toughness of the two samples. The reason for the relatively low impact energy of the S10 sample compared with other similar high-Mn steels was discussed.