Overview of processing, microstructure and mechanical properties of ultrafine grained bcc steels

Ultrafine grained steels with grain sizes below about 1 μm offer the prospect of high strength and high toughness with traditional steel compositions. These materials are currently the subject of extensive research efforts worldwide. Ultrafine grained steels can be produced either by advanced thermomechanical processes or by severe plastic deformation strategies. Both approaches are suited to produce submicron grain structures with attractive mechanical properties. This overview describes the various techniques to fabricate ultrafine grained bcc steels, the corresponding microstructures, and the resulting spectrum of mechanical properties.