Effect of aging treatment on mechanical properties and pitting corrosion of a Cu-bearing multi-phase stainless steel

To bridge the long-standing trade-off between mechanical strength and corrosion resistance in stainless steels, this study investigates the impact of aging temperatures (450 °C to 600 °C) on a novel Cu-bearing multiphase stainless steel (MPSS). The microstructure consists of martensite ( ), δ-ferrite (δ), and retained/reversed austenite (RA), forming a heterogeneous architecture. Experimental results reveal that aging treatments trigger the dual evolution of reversed austenite formation and nanoscale precipitation. Specifically, aging at 500 °C induces a high density of coherent Cu-rich nanoprecipitates (∼9.8 nm) and increases the RA fraction to 13.5%, leading to an optimal strength-ductility synergy with a tensile strength of 1308 MPa and a total elongation of 22.9%. However, increasing the aging temperature to 600 °C results in a drastic decline in both mechanical and corrosion performance. This deterioration is primarily attributed to the interfacial precipitation of the Mo-rich R phase. The R phase not only induces grain boundary embrittlement, but also causes localized Mo depletion, which collapses the pitting potential ( E pit ) from ∼306 mV to a mere ∼35 mV.