2022 Volume 63 Issue 8 Pages 1170-1178
This study aimed to observe the thickening of the S-phase and Sα-phase of various stainless steels subjected to low-temperature direct current plasma nitriding using screen (S-DCPN). Austenitic stainless steel SUS304, ferritic stainless steel SUS430, and duplex stainless steel SUS329J4L were treated using two different screens for comparison, namely, a Ni screen and a steel plate cold commercial (SPCC) screen. Plasma nitriding was performed at 673 K for 300 min under a 75% N2 + 25% H2 atmosphere at 100 Pa pressure of the mixed gas. After nitriding treatment, the samples were examined using X-ray diffraction (XRD) and glow discharge optical emission spectrometry (GD-OES), and their cross-sectional microstructure and surface microstructure were examined using an electron probe micro analyzer (EPMA). Nitrided samples were also subjected to Vickers hardness and pitting corrosion tests. Examination of the SUS304 samples revealed thickening of its S-phase and higher surface hardness and pitting corrosion resistance when nitriding was done with the Ni screen. This was due to excess nitrogen diffusion into the sample due to presence of the Ni screen than with the SPCC screen. In the SUS430 samples, thickening of the Sα-phase was not be observed. When the Ni screen was used during nitriding, higher surface hardness and less pitting corrosion resistance of sample were observed, along with enhanced nitrogen diffusion than the SPCC screen was used. In the SUS329J4L samples, upon nitriding with Ni screen, thickening of the S-phase was observed and surface hardness and pitting corrosion resistance of the sample were higher, which was attributed to the enhanced nitrogen diffusion into the sample than when nitriding with the SPCC screen.
This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 86 (2022) 62–70.