Formation of ultrafine-grained structure in metals and alloys during severe plastic deformation (SPD) at low temperature is established well known. But not always the nanoscale structure can be obtained. This work shows the possibility of additional refinement of structure up to nanocrystalline state (grain size less than 100 nm) in Al- and Fe-based alloys due to phase transformations during SPD by torsion under high pressure.

The aim of this paper is to consider the features of structure evolution during severe plastic deformation (SPD) of steels and its influence on mechanical properties. The investigations have been carried out mainly on low-carbon steels as well as on austenitic stainless steels after SPD by torsion under high pressure (HPT) and equal-channel angular pressing (ECAP). Structure formation dependences on temperature deformation conditions, strain degree, chemical composition, initial state and pressure are considered. The role of phase transformations for additional grain refinement, namely, martensitic transformation, precipitation of carbide particles during SPD and heating is underlined.