where B is a constant with a unit of m s−1, s* the thermal component of the flow stress s, so the stress required for dislocations to have velocity B and n the dislocation velocitystress exponent. Even though the nominal strain rate is kept constant during deformation, the actual true plastic strain rate changes perpetually so that neither the mobile dislocation density nor the average dislocation velocity can be kept constant. If the velocity is not kept constant, the thermal component of flow stress cannot be constant during deformation