First-principles alloy theory is used to establish the gamma-surface of Fe-Cr-Ni alloys as function of chemical composition and temperature. The theoretical stacking fault energy (SFE) versus chemistry and temperature trends agree well with experiments. Combining our results with the recent plasticity theory based on the gamma-surface, the stacking fault formation is predicted to be the leading deformation mechanism for alloys with effective stacking fault energy below similar to 18 mJ m(-2). Alloys with SFE above this critical value show both twinning and full slip at room temperature. Interestingly, twinning remains a possible deformation mode in addition to full slip even at elevated temperatures, in line with observations. (C) 2016 AIP Publishing LLC.