Energy dissipation and plastic flow instability were investigated in P91 steel and Ms70 brass on the basis of continuous tests carried out on Setaram and Gleeble plastometers. Mathematical evaluation of continuous curves was supported with calculation of larger range of input parameters using the "sin h" equation. For energy dissipation calculation strain rate sensitivity parameter (m=(d ln σ)/(d ln ė)) was computed and further the efficiency according to the η=2m/(m+1) formula. Equation ξ=(∂ ln(m/(m+1)))/(∂ ln ė)+m was utilized for the instability parameter calculation. The results were evaluated using Sigmacon, Gnuplot and Golden Surfer computer softwares. The final results are 2D and 3D material processing maps. Results of tests carried out with P91 steel and Ms70 brass were compared to experimental results of other authors with high correlation.