“…Calculation of the hot deformation activation energy from experimental σ p -values on the basis of the hyperbolic-sine Eq. ( 1) is an established method that was successfully applied for different types of materials, recently for example for various types of steel [11][12][13], intermetallic compounds [14], alloys based on copper [15,16], titanium [17,18] or magnesium [19,20], etc. The use of the peak stress σ p seems to be physically justified in this case, because for different Z-parameter values it corresponds to qualitatively similar structural states given by the initiation of dynamic recrystallization; similarly, in the case of the stress σ ss (MPa) corresponding to steady state.…”