A Study On Ion Sulfurization For Bearing Steel And The Mechanism & Application Of Compound Lubrication Technology

Rolling bearings usually work at high pressure and rotation speed for carrying load and transmitting the movement. The wear of raceway and roller of bearings is the main failure mode and factor to determine the service life of bearings. The anti-wear property of contact surfaces under boundary lubrication can be obviously improved by using solid lubrication technology. FeS is a typical solid lubricant. Iron sulfide (FeS) films can be easily prepared on the steel surface using low-temperature ion-sulfuration technique, and the sulfide layer can improve the lubrication state of steel surface and enhance their anti-wear properties. The sulfide layer on the 52100 steel surface is usually very thin, so its anti-wear effect is insufficient under harsh conditions.In order to improve the tribological properties of sulfide layer under harsh contions, the sulfur-containing extreme pressure anti-wear additives and FeS micro-partices were added in the lubricant based on the idea of using the additives to replenish the loss of sulfide layer in the wear process. The synergistic effect between additives and sulfide layer under the lubrication of oil and grease was investigated by a self-made friction and wear tester GWL-1000. SEM equipped with EDS were employed to observe the morphologies of surface, cross-section and wear scar of films, XRD was adopted to detect the surface phase structure. AES was used to detect the elements variation along depth of the sulfide layer and XPS was adopted to identify the valence state of boundary lubrication film.The experimental results showed that the FeS layer has been formed on the steel surface, its thickness is about 1~5μm. The anti-wear properties of bearing steel under oil lubrication can be improved remarkably when using low-temperature ion-sulfuration technique. But the sulfide layer would lose its solid lubrication effect under harsh conditions. The synergistic effect between sulfide layer and sulfur-containing additives will be not good when the FeS layer is destroyed under harsh condition in a short time. However, the composite lubrication can possess an ideal synergistic effect when the FeS layer can last a longer time. The wear properties of plain disk and sulfurized disk can be obviously improved when lubricated by the oil containing FeS particles. The composite lubrication effect of sulfide layer and FeS particles in oil is better than that by single lubrication. The friction and wear properties of bearing steel with sulfide layer and under grease lubrication with FeS particles show also obviously impoved results, however, the good synergistic effect for duplex use of sulfide layer and FeS particles in grease can be found only under the condition of low speed and high loading.The research of this dissertation demonstrated that the composite lubrication of suitable additive and sulfide layer can signicantly increase the tribological properties of friction-pairs under harsh conditions.