Characteristics of the nitrided layer formed on AISI 304 austenitic stainless steel by high temperature nitriding assisted hollow cathode discharge

A series of experiments have been conducted on AISI 304 stainless steel using a hollow cathode discharge assisted plasma nitriding apparatus. Specimens were nitrided at high temperatures (520–560 °C) in order to produce nitrogen expanded austenite phase within a short time. The nitrided specimen was characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, potentiodynamic polarization and microhardness tester. The corrosion properties of nitrided samples were evaluated using anodic polarization tests in 3.5% NaCl solution. The nitrided layer was shown to consist of nitrogen expanded austenite and possibly a small amount of CrN precipitates and iron nitrides. The results indicated that rapid nitriding assisted hollow cathode discharge not only increased the surface hardness but also improved the corrosion resistance of the untreated substrate.