Synergistic Effect of Al and Ni on Microstructure Evolutions and Mechanical Properties of Fe-Mn-Al-C Low-Density Steels

In this study, the synergistic behavior of Ni and Al in two low-density steels (Fe-26Mn-10.2Al-0.98C-0.15V (wt. %) and Fe-29Mn-5Al-1C-12Ni (wt. %)) and their influence on microstructures and mechanical properties were investigated. The chemical composition of κ-carbides and B2 precipitated particles as a function of annealing and aging temperature and the matrix within which they formed were elucidated. The microstructures and deformation mechanisms of both steels were studied based on their strengthening contribution. The Fe-26Mn-10.2Al-0.98C-0.15V steel mainly realized precipitation strengthening through κ-carbides and grain boundary strengthening due to full recrystallization. The strengthening caused by Fe-29Mn-5Al-1C-12Ni steel was mainly due to the presence of the B2 phase in the matrix, which was non-coherent with FCC. This led to the Orowan bypass mechanism, which made precipitation strengthening the main strengthening contribution. The synergistic effect led to the shear or bypass mechanism of both steels when plane dislocation slip occurred. In addition, it also had an influence on the work-hardening capability during plastic deformation. This study provides a promising way to further enhance the yield strength of low-density austenitic steels through the synergistic effect of Ni and Al.