Performance enhancement by plasma nitriding at low gas pressure for 304 austenitic stainless steel

Plasma nitriding was conducted at low gas pressure and low temperature of 400 °C for 304 austenitic stainless steel. The combined performance of the treated specimens was evaluated by scanning electronic microscopy (SEM), X-ray diffractometer (XRD), microhardness tester, ball-on-disc tribometer and electrochemical polarization. The results showed that an expanded austenite (γN), also called S phase layer was formed after plasma nitriding at low gas pressure and low temperature of 400 °C, and the nitriding efficiency was significantly improved at lower gas pressure; maximum expanded austenite layer of 51.7 μm and effective hardening layer of 72 μm were obtained at low gas pressure of 100 Pa. Surface hardness and wear resistance were enhanced dramatically by plasma nitriding at 100 Pa, and the weight loss after wear test decreased from 0.102 g to the minimum of 0.013 g. Meanwhile, the corrosion resistance was improved after plasma nitriding at 100 Pa, the minimum corrosion current of 0.009 μA ·cm−2 and the maximum corrosion potential of −361.9 mV are obtained.