Precipitation behavior of Cu/Ni(Mn,Al) co-precipitates in the medium-Mn dual-phase steel

Abstract

• High Mn content promotes the partition of Mn to NiAl by occupying Al sublattice. • Cu/Ni(Mn, Al) co-precipitates are formed just in the martensite of the DP steel. • The growth of precipitates doesn’t follow volumetric diffusion-controlled process. The precipitation behavior of Cu/Ni(Mn,Al) co-precipitates in the medium-Mn dual-phase (DP) steels was investigated through a combination of atom probe tomography (APT) and small-angle neutron scattering (SANS). The results reveal that high Mn content of the DP steel promotes the partition of Mn to NiAl nanoprecipitates by occupying the Al sublattice, thereby forming a Cu/Ni(Mn,Al) co-precipitates in the martensite. The growth of the co-precipitates doesn’t follow the volumetric diffusion-controlled process, which is controlled by the coupled diffusion of multiple chemical elements induced by the synergistic phase transformation. The coarsening coefficient of the co-precipitates in the DP steel are ten times more than it in the previous martensitic steel, leading to the change of precipitation strengthening effect. The mechanism for the co-precipitates’ coarsening is also addressed and discussed.