Martensitic stainless steel is widely used for medical apparatus, but it can carry a large number of bacteria and cause a potential risk of infection because it has no antimicrobial ability. In this paper, nitriding of 4Cr13 and 8Cr17 martensitic stainless steel was conducted to improve the antibacterial activity. The surface morphology and phase constituents of nitrided 4Cr13 and 8Cr17 specimens were characterized using scanning electron microscopy and X-ray diffraction. Nitrogen concentration profiles in the cross sections of the nitrided specimens were obtained by glow discharge spectroscopy. The antibacterial properties of this nitrided layer were evaluated by a plate-counting method. The antimicrobial ratios of nitrided 4Cr13 and 8Cr17 martensite stainless steel against Staphylococcus aureus were 98.13 % and 99.22 %, respectively, after 12 h. The results showed that the formations of chromium nitride (CrN) and two iron nitrides (Fe3N and Fe4N) are of vital importance to the antibacterial properties of martensitic stainless steel.
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