Designing gradient nanograined dual-phase structure in duplex stainless steel for superior strength-ductility synergy.

• A gradient nanograined dual-phase structure was produced in 2101 duplex stainless steel. • A superior combination of strength and ductility was achieved by superposition of gradient nanostructure and lamellar dual-phase structure. • Strong hetero-deformation induced strengthening and hardening effect contributes to the superior mechanical properties. Similar to other metallic materials, duplex stainless steel dramatically loses its advantage of high ductility as they are strengthened. Here, we produce a gradient nanograined dual-phase structure in the 2101 duplex stainless steel, thus facilitating a superior strength-ductility synergy: a yield strength of 1009.5 MPa being two times higher than that of the as-received sample, a total elongation of 23.4% and a uniform elongation of 5.9%. This novel structure is produced through a processing route of ultrasonic severe surface rolling and annealing, which realizes a superposition of gradient nanostructure and lamellar dual-phase structure with austenite and ferrite. During the tension deformation of gradient nanograined dual-phase structured duplex stainless steel, a significant accumulation of geometrically necessary dislocations occurs. These dislocations are formed to accommodate the deformation incompatibility caused by the layer-by-layer difference in strength and hardness of individual phase domains, as well as the inherent difference in properties between the austenite and ferrite domains. This results in a stronger hetero-deformation induced strengthening and hardening significantly contributing to superior mechanical properties. Our study provides a new avenue to develop advanced steels with high strength and ductility. [Display omitted] [ABSTRACT FROM AUTHOR]