Changes in the grain structure of metallic materials upon plastic treatment

Abstract

Experimental data on structural changes in the process of plastic deformation of polycrystalline copper and stainless steel have been reviewed. It has been shown that the mechanisms of the formation of a new grain structure, i.e., dynamic recrystallization, depend on the conditions of treatment or flow stresses at the steady-state stage, which are determined unambiguously by the temperature and strain rate. Upon hot deformation (low flow stresses), it is local migration (bulging) of grain boundaries and subsequent growth of these bulgings that seem to be the main mechanism of formation of new grains. Since the nucleation of new grains in this case is of a heterogeneous character, the microstructure evolution can be classified as a discontinuous dynamic recrystallization. Upon worm or cold deformation (high flow stresses), we deal with a dynamically recrystallized structure only after very high degrees of deformation. The new grain structure is formed due to the growth of angular misorientation between subgrains with an increase in the total degree of deformation, which can be considered as a continuous dynamic recrystallization. Changes in the mechanisms of dynamic recrystallization with changes in the conditions of treatment lead to a bimodal dependence of the size of dynamically recrystallized grains on the flow stresses.