Plasma nitriding of mirror-finished austenitic stainless steel

Plasma nitriding was earned out on austenitic stainless steel (SUS304) by a low power electron beam induced plasma source. The electron beam, a function of the electron energy and beam current, is independently controlled. Besides, the apparatus incorporates a grid-type electrode that repels the ions but allows neutral particles to reach the workpiece surface. The nitriding process was done in 25% Nj, 50% H:, and 25% Ar gas delivery at a working pressure of 0,5 Pa. The treatment time was 3 hours under 350°C, 400°C, and 450°C processing temperatures. The results of our experiments show that at lower processing temperatures of 350 and 400°C, the formation of the expanded austenite lattice (S-phase) was confirmed by x-ray diffraction (XRD) and micrographs of the etched cross-sections, respectively. The measurements of the S-phase layer show increased hardness distribution and higher corrosion resistance compared to that of the untreated austenitic stainless Steel. On the other hand, the measured surface roughness at 350°C and 400°C were RMS values of 15nm and 25nm, respectively compared to 7nm for the untreated surface. This shows that the controlled plasma nitriding system was an effective and beneficial method for treating high precision mechanical components that need to retain the mirror-finish after plasma nitriding the preferred austenitic stainless Steel. © 2020 Japan Society for Precision Engineering. All rights reserved.