New Development in Through Hardened Bearing Steel Grades for Use in Contaminated Lubrication

摘要

Bearing steel quality has been improved over the past decades by reducing the level and the size of nonmetallic inclusions. Therefore, fatigue lifetime of bearings is mainly governed by surface damage, such as debris denting due to foreign particles. Numerous studies have been performed to find out new steel grades or heat treatments to cope with such severe in-service conditions. Most of these studies argued that the level of retained austenite is the main parameter which governs fatigue lifetime. The present study relates to the effect of heat treatment and alloying elements on the fatigue lifetime of bearing steel in contaminated lubrication at room temperature. Several through hardened steel grades have been tested with different methodologies in order to investigate their behavior in case of: (1) Debris denting, (2) Resistance to Tempering, and (3) High loading conditions. An experimental procedure developed by FAG to simulate particle indentation on bearing has been used to study the behavior of each grade. On the other side, torsion tests at room and high temperature have been used to determine the evolution of fatigue limit. At last, flat washer testing at 4200 MPa is used to determine fatigue lifetime in high loading conditions. Results of fatigue tests are presented in this paper and analyzed in terms of tempering resistance and level of retained austenite.