New Routes for Fabricating Ultrafine-Grained Microstructures in Bulky Steels without Very-High Strains

Several routes to produce ultra fine-grained structures in steels without severe plastic deformation are introduced. The key point of the ideas is to combine plastic deformation with the phase transformation of matrix phases. When as-quenched martensite in steels is used as a starting microstructure, sub-micrometer grain-sized structures can be obtained easily. Another example using a dual-phase steel composed of soft and hard phases is also discussed. Repeating plastic deformation and phase transformation is also effective in obtaining nanostructures in an austenitic stainless steel. Examples of strips of UFG stainless steels in industry and their applications are presented.