ROLLING CONTACT FATIGUE BEHAVIOR OF AN ULTRAHIGH CARBON STEEL

With the development of modern industrial equipment and the requirement in energy conservation and emission reduction, the traditional high carbon and high chromium steel which is widely used as bearing material cannot meet these demands. Therefore, it is of paramount importance to exploit novel materials used as bearings with long life. In recent years, some new techniques have been used to improve the bearing life, such as physical vapor deposition (PVD), chemical vapor deposition (CVD) and plasma immersion implantation and so on. All these techniques are attempting to increase the surface hardness of the bearing. Though the bearing life has been extended to some extent, the application range of these techniques is limited by the price factor and the dimensions of components. Ultrahigh-carbon steels (UHCSs) have been studied for many years, and they possess outstanding mechanical properties and wear resistance. Therefore, it is interesting to explore the probability whether UHCSs can be used in the bearing application. It is well known that if bearings are well assembled, lubricated and loaded, rolling contact fatigue (RCF) is the main failure form. Accordingly, the evaluation of the resistance to RCF is of paramount importance for bearing materials. The RCF properties of UHCSs have never been studied in the past decades. Therefore, in this work, the RCF behavior of a UHCS with 1.29%C (mass fraction) was investigated in well lubricated conditions, using a flat washer-type RCF tester. In order to shorten the testing time, the maximum Hertzian stress was set as 4400 MPa. For comparison, the RCF lives of conventional GCr15 and SKF3 bearing steels were also tested under the same conditions. The results showed that the rated life L-10 of the UHCS was 2.14 and 1.81 times longer than those of the GCr15 and SKF3 steels, respectively. Since more spherical residual carbide particles could be used to retard the grain growth during austenitization for the UHCS, the prior austenite grain size of the UHCS was only 6.91 mu m. However, the prior austenite grain sizes of the GCr15 and SKF3 steels were 13.52 and 11.41 mu m, respectively. Therefore, the average size of martensite plate of the UHCS was approximately half of those of the GCr15 and SKF3 steels. Finer grains were expected to retard the crack initiation and propagation, and then the RCF life would be prolonged. On the other hand, the carbon content and the volume fractions of precipitates in the martensite plates of the quenched and tempered UHCS were both higher than those of the GCr15 and SKF3 steels. These factors made the UHCS harder than GCr15 and SKF3 steels, which was beneficial for the improvement of RCF life.