Strong yet ductile low-density steel via multiphase heterogeneous microstructure

Under equivalent stiffness conditions, material substitution based on a thin-walled design is crucial for the lightweight of components. Developing high-performance steels with both high-yield strength and excellent ductility has become a key focus in fields like aerospace and low-altitude flight. The novel low-density steel presented here exhibits a yield strength of 1 000 MPa, which is 2–3 times higher than conventional low-alloy high-strength steels, while maintaining an elongation of about 18.7%. By combining ex-situ experimental characterization with a phase mechanical response model based on the iso-work theory and the von Mises equivalent method, the role of heterogeneous deformation-induced strengthening was revealed. The calculated values align closely with experimental results. This exceptional performance is attributed to a multiphase heterogeneous microstructure, where fresh martensite, bainite/tempered martensite, and deformation-induced martensite act as hard regions. These regions release micro-stresses through inhomogeneous cooperative deformation with soft ferrite, enabling multiple plastic deformation mechanisms and stress concentration relief. This research offers new insights into optimizing microstructures through mechanical metallurgy, which is crucial for producing high-performance, lightweight components.