Effect of Cu addition on the microstructure and the mechanical properties of austenitic low-density steel

Abstract

In this study, austenitic low-density steels with 0, 1, and 3 wt% Cu additions were subjected to various solid-solution and aging treatments to examine their microstructural evolution and mechanical properties. After solution treatment at 950–1050 °C, all steels exhibited a single-phase austenitic structure. The addition of 3 wt% Cu caused the austenite softening, but it could effectively inhibit grain growth during the increase of solution treatment temperature, thereby enhancing grain boundary strengthening. In the aged state, high-density intragranular κ-carbides precipitated in all steels, while only a small amount of intergranular Cu-rich particles was observed in the Cu-containing steels. Furthermore, the addition of 3 wt% Cu promoted the formation and growth of κ-carbides, leading to an enhanced precipitation strengthening and a significant improvement in strength. The predominant deformation mechanism was dislocation glide in all steels. Strain hardening was attributed to dynamic slip band refinement, and Cu alloying contributed to reducing the spacing of slip bands. As a result, the Cu-containing steels achieved a higher work hardening rate and greater fracture elongation.