An international research team has applied a chemical boundary engineering approach to the realization of lightweight, inexpensive steel with high tensile strength and high ductility. When applied to plain steels with carbon content of only up to 0.2 wt %, the method yields ultimate strength levels beyond 2.0 gigapascal and Electron backscatter diffraction image map (A) with superposed phase color map of the face-centered cubic phase (red region) of processed steel. (B) Sketch of the microstructural evolution of the steels during ultrafast heating and quenching and (C) the ultrafine dual phase microstructure processed steel. Source: R. Ding et al.ductility exceeding 20%.

High temperature processing was used to alter the chemical boundaries, or interfaces where a material maintains its crystal structure but shifts its elemental composition, of a low carbon steel. After cold rolling and a standard austenite reversion treatment, the steels were rapidly heated at a temperature increase rate of greater than 100° C/s and then immediately quenched to ambient temperature.

The rapid heating eliminates all austenite/ferrite phase boundaries and many grain boundaries, resulting in the formation of micro- and nano-structures as the material cools. The ultrafine duplex microstructure consists of ferrite with equal dimensions in all directions and metastable austenite, with mean grain diameters of 340 and 290 nm, respectively. These structures can nearly double the strength of the original steel without sacrificing flexibility.

Researchers from Tsinghua University (China), Max-Planck-Institut für Eisenforschung (Germany), Ruhr-Universität Bochum (Germany), Tohoku University (Japan) and Delft University of Technology (The Netherlands) contributed to this study, which is published in Science Advances.