Design of ultra-strong but ductile iron-based alloys with low supersaturations

High-performance but low-cost structural materials with nanoscale precipitations are vitally important for engineering applications in advanced industry systems. Thus far, the classical nucleation mechanism assumes a critical nucleus of a homogeneous composition up to a sharp boundary with a large energy barrier of nucleation. A fine dispersion of nanoscale precipitates often requires strong solute supersaturations with expensive alloying additions or otherwise deteriorated strength-ductility, weldability, and fabricability. The simultaneous satisfaction of all these mutually exclusive requirements is the longstanding issue for the design of advanced materials for structural applications. In this alloy design, we have adopted a revolutionary approach of ultra-strong iron-based alloys that have resolved all these key issues through non-classical nanoscale precipitations and multi-elemental partitioning. Such an alloy design strategy offers a unique approach to control nanoscale precipitates with low solute supersaturations. Fine precipitations so designed lead to the strong enhancement of both the precipitate-dislocation interactions and work-hardening capacity, resulting with a sharp increase of the yield strength (YS) to as high as 1500 MPa and tensile ductility up to 15%. Furthermore, our design assures outstanding fabricability together with superior post-weld properties through dense nanoscale reprecipitations (∼10²⁴ m⁻³) in a well economical manner for production. The non-classical actions unfold brand new pathways for precipitation of various intermediate structures and chemistries with low energy barriers, especially useful for the design of sustainable and economical modern alloy systems. © 2023 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.