1. An analytical expression, verified by experiment, is proposed for determining to a first approximation the true value of the degree of deformation of material in DHP. Equations are derived describing the relationship between this quantity and the initial porosity and degree of macrodeformation of a blank. 2. A study was made of the effect of the degree of deformation of material in the DHP of iron on its grain size. The critical value of the degree of deformation of material (6–8%) was determined at which the resultant iron grain size is a maximum.