Role of Mn in partitioning behavior and precipitation evolution in multicomponent Fe-Cu-based steels

This study investigates the role of Mn partitioning in the precipitation behavior and mechanical properties of Fe-Cu and Fe-Cu-Ni-Al steels. In Fe-Cu steel, fine Cu precipitates form at a high number density within a ferritic matrix upon aging. Mn addition enhances hardenability and induces martensite formation, doubling the geometrically necessary dislocation density. Mn enriches within the Cu-rich precipitates and accelerates Cu precipitation kinetics, producing an early peak hardness of 367 HV after 5 min followed by softening to 298 HV after 60 min. Further addition of Ni and Al redirects Mn toward NiAlMn precipitates, promoting Cu and NiAlMn co-precipitation and compositional partitioning. This redistribution modifies the co-precipitation pathway, retains a higher number density of fine Cu-rich precipitates, and reduces the preferential enlargement of coarse particles. The Fe-Cu-Ni-Al-Mn steel achieves high hardness (404 HV after aging for 10 min) and strength (ultimate tensile strength of 1,200 MPa after aging for 20 min) through the combined effects of a martensitic matrix and Cu and NiAlMn precipitation strengthening. These findings identify Mn as a regulator of solute partitioning and precipitation stability, and provide guidance for the compositional design of multicomponent nanoprecipitation-strengthened steels.