Microstructure, corrosion and mechanical properties of 304 stainless steel containing copper, silicon and nitrogen

The effects of 0.086–0.336% nitrogen additions on the microstructure, corrosion and mechanical properties of type 304 austenitic stainless steel (SS) containing 2% copper and 2–3% silicon were studied. This study was carried out using scanning electron microscope (SEM), potentiodynamic, weight loss, hardness number and ball-punch bulge measurements. Mutual effects between Si and N were observed in the matrix of SS. Nitrogen offset the ferrite-forming tendencies of Si and was more efficient than Ni as austenitizer, but Si decreased the solubility of N in solid solution. N additions improved the pitting resistance of SS in acidic and neutral chloride solutions. This was more evident in more aggressive solutions than in solutions with low chloride concentrations. Segregation of second N-rich phases, like Cr2N, in SS containing 2% Cu, 3% Si and 0.237% N was occurred. This steel exhibited less pitting corrosion resistance than the plain 304 SS in most chloride solutions under study. Addition of 2% Si to 304 SS containing Cu has negative effect on the mechanical behavior. But presence of N improved the mechanical strength of steel irrespective of the drop solubility of N affected by Si.