so that the flow stress is given as a function of the true plastic strain o with seven variables of so, B, rm, n, U, V and r0 as long as the true plastic strain rate is specified. The computer simulation is carried out by using a non-linear curve fitting software called ‘Peakfit®’ from Jandel Scientific. Although the effect of grain size and/or dispersion of second-phase particles on the flow stress is not expressed clearly in this equa- tion, the deformation parameters obtained in the present simulation may inclusively reflect their effects.