2.1 GPa ultra-strong nanostructured steel with unexpected large ductility

Abstract

There has been an increasing demand for high-performance steels for the construction of energy-efficient and lightweight structures in aerospace and automotive industries. High-performance steels require ultrahigh strength as well as good ductility. Nevertheless, strength and ductility are mutually exclusive. It is extremely challenging to design an ultrahigh strength steel with good tensile ductility, especially steels with yield strength higher than 2 GPa. The present work proposes a new method to meet such a challenge to produce an ultrastrong and ductile steel with a yield strength of 2.1 GPa and an unexpected large tensile uniform elongation of 20%. To the best of our knowledge, this steel may be the best so far in terms of the combination of yield strength and uniform elongation compared to those reported in the open literature. The present novel steel possesses a dual-phase hierarchical nanostructure consisting of nanosized precipitates, nanotwins, and lamellar nano- and ultrafine-grained austenite and ferrite. This novel steel has been strengthened by all the available strengthening mechanisms, including solid-solution, precipitation, dislocations, grain boundary and twin boundary strengthening. Besides dislocation plasticity, the novel steel also experiences transformation-induced plasticity (TRIP) as well as twinning-induced plasticity (TWIP). More importantly, different to other lab-scale methods of producing ultrahigh strength alloys, such as the severe plasticity deformation (SPD) technique, the present novel steel has been produced by conventional processing routes currenlty used in the steel industry. No additional facilities are required for the steel industry to produce this novel steel, which will facilitate its future industrial application.