Wear properties of steel plasma nitrited at high temperatures

Abstract

The wear behaviour of 722M24 (En40B) steel plasma nitrided at high temperatures for long durations was investigated. Under dry sliding and abrasive-containing lubricated conditions, the wear characteristics of the steel were studied as a function of load, time and white layer thickness. The white layer and the wear debris were characterized by X-ray diffraction. The topography of the wear surface was examined in a scanning electron microscope. The plasma nitriding process was carried out by using a 20 kW plasma processing unit in cracked ammonia atmosphere. Treatment time of up to 100 h were employed with temperatures of 550, 570 and 590 °C. Wear tests were performed with plasma nitrided AMS 6472 as the counterface material. The tests under abrasive-containing lubricated conditions were carried out with 10% carborundum powder 10 μm in size in SAE-30 machine oil. The wear resistance of the steel was improved by plasma nitriding and the abbrasive wear resistance of nitrided steel was higher than the wear resistance under dry sliding conditions. However, the surface hardness and white layer thickness are very important factors in the wear behaviour of steel.