Tensile deformation of a duplex Fe-20Mn-9Al-0.6C steel having the reduced specific weight

The room temperature deformation characteristics of a duplex Fe-20Mn-9Al-0.6C steel with the reduced specific weight of 6.84 g/cm³ in the fully solutionized state were described in conjunction with the deformation mechanisms of its constituent phases. The phase fraction was insensitive to annealing temperature in the range of 800-1100 °C. The ferrite grain size was also nearly unaltered but the austenite grain size slightly increased with increasing annealing temperature. This revealed that there is little window to control the microstructure of the steel by annealing. The steel exhibited a good combination of strength over 800 MPa and ductility over 45% in the present annealing conditions. Ferrite was harder than austenite in this steel. Strain hardening of both phases was monotonic during tensile deformation, but the strain hardening exponent of austenite was higher than that of ferrite, indicating the better strain hardenability of austenite. In addition, the strain hardening exponent of austenite increased but that of ferrite remained unchanged with increasing annealing temperature. The overall strain hardening of the steel followed that of austenite. Considering element partitioning by annealing, the stacking fault energy of austenite of the steel was estimated as ∼70 mJ/m². Even with the relatively high stacking fault energy, planar glide dominantly occurred in austenite. Neither strain induced martensite nor mechanical twins formed in austenite during tensile deformation. Ferrite exhibited the deformed microstructures typically observed in the wavy glide materials, i.e. dislocation cells. The mechanical properties of the present duplex steel were compared to those of advance high strength automotive steels recently developed.