The present paper deals with the generation of hard layers in the vicinity of frictional interfaces in metal forming processes. The primary objective of the paper is to introduce a general approach to relate the strain rate intensity factor and parameters that characterize the microstructure and thickness of such layers. This approach is used in conjunction with axisymmetric direct extrusion of an AZ31 alloy. The thickness of the hard layer is determined experimentally. Also determined is the distribution of average grain size and hardness near the friction surface. The strain rate intensity factor is found using an available semi-analytical solution.