AbstractThe brittle–ductile transition temperature (DBTT) is not intrinsic to a material but depends on the specimen type and loading mode used for the test. The influence of these parameters is related to the plastic constraint. Here the constraint is evaluated by the effective T stress obtained by the stress different method on the notch tip stress distribution. From Charpy energy values at different temperatures, it is possible to get a material failure master curve (MFMC) where the notch fracture toughness is plotted versus the shift of test temperature with the transition temperature corresponding to the effective T stress value.