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Abstract

Mechanically strong and ductile load?carrying materials are needed in all sectors, from transportation to lightweight design to safe infrastructure. Yet, a grand challenge is to unify both features in one material. We show that a plain medium-manganese steel can be processed to have a tensile strength >2.2 gigapascals at a uniform elongation >20%. This requires a combination of multiple transversal forging, cryogenic treatment, and tempering steps. A hierarchical microstructure that consists of laminated and twofold topologically aligned martensite with finely dispersed retained austenite simultaneously activates multiple micromechanisms to strengthen and ductilize the material. The dislocation slip in the well-organized martensite and the gradual deformation-stimulated phase transformation synergistically produce the high ductility. Our nanostructure design strategy produces 2 gigapascal?strength and yet ductile steels that have attractive composition and the potential to be produced at large industrial scales. High-strength steels with good ductility are attractive for a number of applications, but these alloys often require the use of expensive elements or complex processing methods. Li et al. found that a high-strength steel composed of iron, manganese, silicon, carbon, and vanadium can be made with a different processing strategy. A combination of forging, cryogenic treatment, and tempering creates an alloy with very high strength that also has good ductility and formability. The strategy should be an option for other compositions of steel. ?BG A different processing strategy creates a high-strength steel with good ductility without expensive elements.