Phase precipitation and corrosion properties of copper-bearing ferritic stainless steels by annealing process

The effects of different annealing processes on the phase precipitation behavior and corrosion properties of copper-bearing 430 ferritic stainless steel were systematically investigated. The shape, quantity and distribution of copper-rich precipitates by different annealing processes were characterized by scanning electron microscopy, transmission electron microscopy, backscatter electron and backscatter diffraction. The pitting resistance behavior in simulated physiological saline environments (0.9 wt.% NaCl) was investigated using electrochemical workstation and X-ray photoelectron spectroscopy. The results showed that the copper-rich phase prepared by repeated rolling and annealing gradually changed from long needle-like to short thick rod-like and granular, whose distribution tended to be uniform and diffusive, and the number of copper-rich phases increased. After solution/antibacterial annealing process, the size and density of the copper-rich phase increase, resulting in a discontinuity of the passivation film on the stainless steel, which reduces the pitting resistance to some extent. The refinement mechanism revealed that pre-deformation brings about a modification in both precipitation mechanism and growth kinetics of epsilon copper.