Friction And Wear Properties Of A High-performance Plasma Nitrided Steel

With the rapid development of China’s machinery manufacturing industry, especially the development of the miniaturization, precision, high-speed trends of the main engine, the quality demands of shaft, bearing, and gear parts material have become higher and higher. The high-performance nitrided steel can meet the requirement for the structure of such parts, with high hardness, high wear and corrosion resistance characteristics. Therefore, it has a broad application prospect. Shaft, bearing, gear parts in the army, friction and wear exist inevitably. However, in the current research sliding wear properties of plasma nitriding steels were mostly focused on, such as frequently-used stainless steels, bearing steels. There have been relatively less researches on the sliding wear characteristics, especially the fretting wear characteristics and rolling contact fatigue performance of high-performance nitrided steel as well as the sliding wear characteristics between high performance nitrided steel and wear-resistant aluminium-bronze alloy. In view of the above-mentioned facts, in the process of research and development of high performance nitrided steel, it has very important engineering significance to study on friction and wear characteristics itself.In this paper the matrix of high-performance steel has been treated by plasma nitriding technology. The surface hardness of the test steel has been up to980HVi.96n, with280μm nitrided layer. Fe2-3N, Fe4N,Cr2N phases have formed during the plasma nitriding processing, examined by X-ray diffraction (XRD), which would be better for the anti-wear resistance of the tested steel.Sliding and fretting wear tests of plasma nitrided steel have been carried out at SRV IV tribo-meter. The results showed that sliding friction and wear characteristics of the nitrided steel have been great influenced by the working conditions. Dry friction, the wear mechanism is mainly abrasive and slightly adhesive at the light load and low speed. However, there has been a massive spalling on the surface of the nitrided steel at the high speed and heavy load. With lubrication, the wear mechanism is mainly abrasive wear at the low speed and light load, While the ploughs became deeper and denser, and tiny spallings perpendicular to the moving direction of were visible at the high speed and heavy load. Plasma nitriding treatment could improve the fretting friction and wear properties of experimental steel. Fatherly, friction coefficient and wear volume decreased respectively by36%,97%, compared with the matrix. Fretting wear mechanism is peeling and oxidation wear.Meanwhile, Contact fatigue test of plasma nitrided steel were done at ball-on-rod test device. The results showed that the rating life (Lio), the median life (L50) and the characteristic life (L63.2) of the nitrided steel are respectively3.3times,4.3times,4.5times of those of the test steel matrix. Compared with the matrix, the distribution of fatigue data of the nitrided steel was relatively narrower, indicating the fatigue data more stable. That is, the distribution of failure time was relatively stable. Fatigue pitting spots were analyzed by the scanning electron microscope. It revealed that the pitting corrosion of the steel was resulted from the surface crack initiation and expanding inward, the main crack perpendicular to frictional direction initiation and propagation as well as the secondary crack expanding, finally the cracks meeting and making the surface layer material fracture.Sliding wear test between high performance nitrided steel and wear-resistant aluminium-bronze alloy has been conducted, too. The results showed that the heat treatment has strengthened copper alloy, the surface hardness increasing but the toughness decreasing. Dry friction, a lubricating film was not prone to form because the wear debris was hard and brittle after heat treatment of the copper alloy, which led a heavy wear between the nitrided steel and the copper alloy. With lubrication, owing to the media and lubricating functions of the oil, the increase of the strength and the surface hardness of the copper alloy has improved the anti-wear resistance itself though the wear of the mating part nitrided steel has been worse.