Derivation and Variation in Composition-Dependent Stacking Fault Energy Maps Based on Subregular Solution Model in High-Manganese Steels

A subregular solution thermodynamic model was used to calculate the stacking fault energies (SFEs) of high-manganese (10 to 35 wt pct) steels with carbon contents of 0 to 1.2 wt pct. Based on these calculations, composition-dependent diagrams were developed showing the regions of different SFE values for the mentioned composition range. These diagrams were called SFE maps. In addition, variations in the SFE maps were observed through increasing the temperature, aluminum content, and austenite grain size. These changes were seen either as an increasing trend of SFE caused by raising the temperature and aluminum content, or as a decreasing behavior caused by increasing the grain size. The SFE value of 20 mJ/m² within these diagrams was introduced as the upper limit for the strain-induced martensite formation. The variations in this limit caused by increasing the temperature and aluminum content were mathematically evaluated to find out the minimum amount of manganese that was required to avoid the martensitic transformation. By introducing the isocarbon and isomanganese diagrams of the SFE, it was seen that both temperature and aluminum had a greater effect on the SFE when added to the steels with the lower manganese contents. Moreover, by adding more aluminum to the composition of the high-manganese steels, its influence on the SFE decreased continuously.