The Fretting Wear of Nitrogen-Bearing Austenitic Stainless Steel at Temperatures to 600°

The fretting behavior of the nitrogen-bearing austenitic stainless steel, Nitronic 60, has been studied at 20, 400, 500, and 600°C in air. A spherical ended rider was vibrated against a flat specimen, both machined from the steel. Normal load was 3N, frequency 50Hz and peak-to-peak amplitude 40 μm. Coefficient of friction after 10⁶ cycles showed a decrease as the temperature was increased, falling from 0.62 at 20°C to 0.10 at 600°C. Wear volume also dropped dramatically at 400° and above, with no measurable wear at 600°C. A smooth protective oxide was formed at 400, 500, and 600°C, typical of the glaze oxide previously found on nickel-based alloys. The oxide layer was approximately 10 μm thick and had the spinel structure. The electron diffraction pattern most closely resembled that of the spinel NiO, Cr₂O₃ but chemical tests showed that it contained iron. It is thought to be a mixed spinel containing all three metal ions.