From conventional steels to high-entropy alloys: progress in the design of high-performance structural materials

3d late transition metal (3dLTM) medium-entropy and high-entropy alloys (MEAs and HEAs, respectively), also known as multiprincipal element alloys or complex concentrated alloys, have emerged as one of the most actively developing and technologically versatile branches of current metallic materials research. Among various HEA families, Fe–Mn–Co–Ni–Cu–Al–C systems and their subsystems offer a good combination of structural flexibility and tunability of phase composition. These relatively lightweight alloys bridge high-Mn steels with MEAs/HEAs and other complex concentrated solid-solution materials. This review provides an integrated analysis of recent progress in 3dLTM HEAs with a specific emphasis on compositional optimization by late 3d transition metals, using classical production routes from industrial steel precursors, and a design strategy originating from the Fe-rich corner of phase diagrams, for achieving high mechanical strength combined with tensile ductility. The mechanisms controlling microstructural evolution under plastic deformation and subsequent strengthening are also evaluated. Modern compositional design, classical heat treatment and deformation processing, short-range ordering, and phase transformation engineering are connected into processing–structure–property relationships. The analysis reveals that Fe–Mn–Co–Ni–Cu–Al–C-based systems HEAs show highly transformable microstructure and good ability for deformation-induced strengthening, while retaining a reasonable tensile plasticity. These features provide useful control over mechanical properties, enabling exceptional combinations of tensile strength (1.5–2 GPa), tensile ductility (4–15%), and Vickers hardness (> 5 GPa), depending on chemical composition, structure and processing conditions. The paper outlines emerging opportunities in alloy design, advanced thermomechanical processing and structure engineering for next-generation structural HEAs and MEAs.