Sliding-vvear evaluation of nitrided austenitic alloys

AbstractThe nitriding behaviour of a number of austenitic alloys was investigated for the temperature range 550–850°C. The maximum response to nitriding, as recorded by weight gain and thickness measurements of the nitride layer, occurred between 660 and 750°C. After an initial, faster rate of nitriding during the first few hours of treatment, the reaction followed parabolic kinetics. With most alloys, the nitride formed a compact layer, essentially composed of M4N, at temperatures up to and including 750°C, although at 850°C unreacted metal remained in the surface regions. An exception to this was a high-nickel (∼ 20%) alloy, in which substantial unreacted metal was found at all nitriding temperatures. The role of different alloying elements is discussed in relation to nitriding performance. A selected nitriding treatment is applied to each austenitic alloy, and the resulting unlubricated wear behaviour evaluated using a pin-on-disc wear machine. A transition from mild to severe wear is identified in tre...