Ultrafine-Grained Stainless Steels after Severe Plastic Deformation

The aim of the present review is to summarize the recent achievements in the development of ultrafine-grained austenitic/ferritic stainless steels processed by large strain deformation. Various aspects of microstructure evolution and its effect on the properties of processed steels are considered. The paper starts from an overview of various methods of large strain deformation that are successfully used for producing ultrafine-grained metallic materials. Then, the structural mechanisms responsible for grain refinement during plastic deformation are considered and discussed from the viewpoint of their efficiency and effect on the subsequent recrystallization behavior. Finally, some physical and mechanical properties of ultrafine-grained stainless steels are observed. It is concluded that the development of ultrafine-grained microstructures during severe plastic deformation results from a kind of continuous dynamic recrystallization. Namely, the misorientations among the strain-induced cells/subgrains progressively increase up to typical values of ordinary grain boundaries. Following the rapid reduction at relatively small strains, the deformation grain size gradually approaches its final value, which depends on alloying/phase content and processing conditions. An increase in the number density of interface/grain boundaries in the initial state significantly accelerates the kinetics of grain refinement during subsequent plastic working.