B2 phase is non-shearable by gliding dislocations unlike the κ-carbides present in TRIPLEX steels (Gutierrez-Urrutia and Raabe 2012; Gutierrez-Urrutia and Raabe 2013; Gutierrez-Urrutia and Raabe 2014; ). An optimisation of B2 phase morphology, and distribution through appropriate thermomechanical processing leads to high strain hardening which is responsible for an excellent combination of high specific ultimate tensile strength (SUTS ~200-230 MPa g -1 cm 3 ) and high specific yield strength (SYS ~150-200 MPa g -1 cm 3 ) in B2s Fe-Mn-Al-Ni-C steels . For instance, cold rolling of Fe-16Mn-9Al-Ni-0.86C (wt.%) steel leads to the formation of B2 phase in the form of stringers whereas annealing at 900 °C (after cold deformation) leads to the nucleation of B2 phase with three possible morphologies: (i) stringer bands, (ii) fine precipitates (size ~200-1000 nm), and (iii) finer precipitates (size ~50-300 nm) . In the context of B2s Fe-16Mn-9Al-5Ni-0.9C (wt.%) steel, the annealed microstructure comprising of B2 stringers in FCC matrix has been described as a Type 1 microstructure (Fig. ) . Nucleation of B2 phase in the form of precipitates (size ~200-1000 nm) at recrystallised FCC grain edges and GBs leads to a Type 2 microstructure (Fig. ) . On the other hand, precipitation of B2 (size ~50-300 nm) at shear bands in deformed (or nonrecrystallised) FCC grains leads to a Type 3 microstructure (Fig. ) . While, Type 2 and Type 3 microstructures enhance the strength, Type 1 microstructure is detrimental for the same .