Role of nanoscale ordering transformation in the design of a strong quadruplex lightweight steel

This study examines the impacts of ordered nanostructures on mechanical properties in a newly designed quadruplex lightweight steel. Aging the D0₃-strengthened duplex lightweight steel drives two ordering reactions: the precipitation of κ-carbides in austenite and the formation of D0₃/B2 intermetallic domains. The steel exhibits excellent mechanical properties, with a yield strength of 1.5 GPa, a tensile strength of 1.7 GPa, and a total elongation of 15 %. Austenite strengthening from κ-carbides and D0₃ softening from B2 intermetallic compounds reduce deformation incompatibility. Moreover, deformation twins are suppressed by κ-carbides. A moderate strain hardening relies on microband-induced plasticity during uniform deformation. In contrast, the very high flow stress overcomes the restriction by κ-carbides and triggers deformation twins during post-necking deformation, improving the post-elongation. This study discloses transformation paths toward the design of strong and ductile lightweight steels, especially with improved post-elongation.