The Initial Precipitation Behavior of Copper in Ferritic Stainless Steel

The precipitation of a suitable amount of Cu phase is the key to the antibacterial performance of Cu-containing antibacterial stainless steel. In order to study the precipitation behavior of Cu in ferritic stainless steel, the nucleation rate–temperature curve and phase transition kinetics curve of the Cu-rich phase were calculated theoretically. The distribution, size, and composition of Cu precipitates were characterized, and the distributions of Ni and Mn in the Cu precipitates at different annealing times were also analyzed by atom probe tomography and transmission electron microscopy. The crystal structure of the Cu precipitates was observed by high-resolution electron microscopy. With an increase in annealing temperature, the nucleation rate decreases and the time for nucleation of Cu precipitates increases monotonously. Accordingly, the size of the Cu-rich phase increases, and the number density decreases with increasing annealing time. Moreover, the contents of Ni and Mn gradually increase, and the Ni and Mn atoms aggregate on the surface of the Cu-rich phase. When the steel is annealed for 60 s, the Cu precipitate in the ferrite matrix exhibits a 9R structure with multiple twins.