2019 Volume 59 Issue 6 Pages 344-349
Low carbon steel sample S15C was nitrided by active screen plasma nitriding (ASPN) and direct current plasma nitriding with screen (S-DCPN) using a chromium screen to form simultaneously chromium nitride coating/nitrogen-diffusion layer on the sample surface. The sample was placed on the sample stage in a floating potential and a cathodic potential. A chromium screen was mounted on the cathodic stage parallel to the top of the sample. Plasma nitriding treatments in a floating potential (ASPN) and a cathodic potential (S-DCPN) were performed in a nitrogen–hydrogen atmosphere with 75% N2 + 25% H2 for 120 min at 773 K and 873 K under 200 Pa. After nitriding, the nitrided microstructure was examined with a scanning electron microscope, glow discharge optical emission spectroscopy and X-ray diffraction studies. In addition, the hardness and corrosion properties were also measured. The nitrided layer formed by S-DCPN consisted of a Crconcentrated layer (~750 HV) followed by a nitrogen-diffusion layer whereas that formed by ASPN consisted of deposited layer of chromium nitrides and iron nitrides without nitrogen-diffusion layer. Corrosion resistance of the sample treated by S-DCPN was better than that of untreated sample and sample treated by ASPN.
