The Effects of Nitrogen Alloying on the Microstructure and Properties of Cu-Bearing Antimicrobial Stainless Steel

In this study, a novel Cu-bearing 304 stainless steel doped with 4.0 wt.% Cu (304-Cu SS) was developed, and the effects of nitrogen microalloying (304N-Cu SS) and heat treatment on mechanical, antibacterial, and corrosion properties were investigated. It was found that when aging at 700 °C, the Vickers hardness and strength of the 304N-Cu SS first significantly increased with increasing aging time up to 4 h and then slowly decreased with further increase in aging time. The best combination of strength and ductility, namely, a yield strength of 319 MPa, ultimate tensile strength of 657 MPa, and elongation to fracture of 47.0%, was achieved in the 304N-Cu SS after aging at 700 °C for 6 h. Moreover, the antibacterial and corrosion rates of the newly developed 304N-Cu SS reached 99.67% and 0.0032 g·m^-2h^-1, surpassing those of 304-Cu SS by 0.38% and 9.4%, respectively. These enhancements in the mechanical, antibacterial, and corrosion properties were attributed to the precipitation of high-density nanoscale Cu-rich precipitates during aging. Our results demonstrate that nitrogen microalloying is an effective metallurgical method for the future development of new antibacterial austenitic stainless steels with simultaneously enhanced mechanical, antibacterial, and corrosion properties for direct drinking water distribution systems.