Study On Contact Fatigue Property Of Bainitic Bearing Steels

Bainite bearing steel GCr15Si1 Mo was used in the paper. Different microstructures were obtained by varying the heat treatment processes and the point contact fatigue tests were performed. Weibull curves were drawn through the statistical contact fatigue life of the specimens. The surface morphologies and volum fractions of phases during the point contact fatigue test were analyzed. The fatigue properties were compared to that of traditional martensite bearing steel GCr15. The results showed that the bainite bearing steel GCr15Si1 Mo exhibited a superior contact fatigue properties in comparision with martensite bearing steel GCr15. During the contact fatigue, the strain-induced retained austenite to martensite occurred in the bainite bearing steel,which was beneficial for improving the contact fatigue property.The effect of voulum fraction of carbide in the bainite bearing steel on the contact fatigue behavior was also investigated. The results showed that the contact fatigue performances of the specimens in the case of oil lubrication conditions were in the order: bainite without carbide, the specimen with 5.1% carbide and the specimen with 1.9% carbide volume fraction. The specimen with 1.9% carbide have a better point contact fatigue life than the specimen with 5.1% carbide during the contact fatige testing without lubrication. The undissolved carbide in the microstructure as the hard phase can be the source of fatigue, shortening the incubation period of crack initiation and consequently deteriorate the fatigue life. Hence, the fatigue life of the bainite without carbide was longer. However, the resutls of the specimens with carbide were oppsite under the contact fatigue with different conditions. One can be concluded that more undissolved carbide among the microstructures with carbide was beneficial for the point fatigue property with oil lubrication of the bainite bearing steel. The carbides dropped off form the surface of the specimen and the pits were formed on the surface during the early stage of the contact fatigue with lubrication. And then the pits on the surface of the specimens increased the adhesion stress between the oil and the surface of specimen, which was in favor of thickening minimum film thickness of the elastic-fluid pressure lubrication and increasing oil film during the testing. And consequently the point contact fatigue life was improved.