Beneficial effects of nitrogen on austenite antibacterial stainless steels

Nitrogen is a significant alloying element in austenite stainless steels. The aim of this paper is to evaluate the effects of nitrogen on the microstructure and properties of austenite antibacterial stainless steels. Two austenite antibacterial stainless steels containing copper and different nitrogen concentration (0.02 and 0.08 wt%, respectively) were fabricated. The microstructures and composition analysis were carried out using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and Auger electron spectroscopy (AES). The epsilon copper-rich precipitates are spherical and less than 20 nm in size, with a cube-on-cube orientation relationship with the matrix. They are dispersed on the steel surface with a mean space of about 200 nm. Nitrogen cannot only improve the antibacterial property but enhance significantly the corrosion resistance in chloride media. Nitrogen compensates the harmful effect of epsilon copper precipitates on the corrosion resistance. The nitrogen concentration in the surface of N-2 steel is four times as much as in the surface of N-1 steel. Nitrogen enrichment in the steel surface improves the corrosion resistance. The presence of higher nitrogen increases the strength and decreases the ductility of austenite antibacterial stainless steel, which could be related to the variation of stacking-fault energy associated with nitrogen concentration.