A sub-regular solution thermodynamic model was used to calculate the stacking-fault energies of high-manganese (10 to 35wt%) steels with carbon contents of 0 to 1.2wt%. Based upon these calculations, composition-dependent diagrams were developed which showed the regions of various stacking-fault energy values for the above composition ranges. These diagrams were termed stacking-fault energy maps. In addition, variations in the stacking-fault energy maps were observed after increasing the temperature, aluminum content and austenite grain size. These changes were seen either as an increasing trend in stacking-fault energy caused by raising the temperature and aluminum content, or as a decreasing behavior caused by increasing the grain size. A stacking-fault energy value of 20mJ/m2 in these diagrams was introduced as the upper limit to strain-induced martensite formation. The variations in this limit, caused by increasing the temperature and aluminum content, were mathematically evaluated to find the minimum amount of manganese that was required to avoid the martensitic transformation. By introducing iso-carbon and iso-manganese diagrams for stacking-fault energy, it was seen that both temperature and aluminum had a greater effect upon the stacking-fault energy when added to steels with lower manganese contents. By adding more aluminum to the compositions of high-manganese steels, its influence upon the stacking-fault energy decreased continuously.

Derivation and Variation in Composition-Dependent Stacking Fault Energy Maps Based on Subregular Solution Model in High-Manganese Steels. A.Saeed-Akbari, J.Imlau, U.Prahl, W.Bleck: Metallurgical and Materials Transactions A, 2009, 40[13], 3076-90