Correlations between the calculated stacking fault energy and the plasticity mechanisms in Fe–Mn–C alloys

A model is proposed for the evaluation of the stacking fault energy (SFE) in Fe–Mn–C austenitic alloys, at different temperatures. It accounts for the variation of the Gibbs energy of each element during the austenite to ε martensite transformation, plus their interactions. The Gibbs energy due to the antiferromagnetic to paramagnetic transition is also taken into account. The required data have been obtained from the literature. The result shows a decrease of the SFE with temperature, with a saturation below the austenite Néel temperature. The result agrees with the mechanical and thermal martensitic transformation limits proposed by Schumann. The plasticity mechanisms depend on the SFE. The mechanical martensitic transformation occurs below 18mJ/m2, and twinning between 12 and 35mJ/m2, in agreement with the tensile tests and the deformation microstructures observed in an Fe–22wt.% Mn–0.6wt.% C alloy at 77, 293 and 693K.