Improved Chemical Composition of Low Alloyed High Carbon Martensitic Bearing Steels for Higher Fatigue Strength

摘要

The average operation temperature of rolling element bearings in standard applications is rising. Due to this advancing demand, the chemical composition of martensitic bearing steels like 100Cr6 (DIN 1.3505; SAE 52100) and 100CrMnSi6-4 (DIN 1.3520) has to be adapted. To enhance the tempering resistance of these steels several alloying approaches concerning the contents of silicon and manganese were tested. The central point of interest in the presented investigation was the influence of the new alloy concept on the lifetime of ball bearings. It could be shown that the lifetime of artificially damaged bearings containing 1.5 % silicon is significantly higher compared to alloys with lower silicon contents. At test temperatures of 120°C and Hertzian contact stresses of approximately 3200 and 3400 MPa, the L_(50) lifetime was about three times higher with 1.5 % silicon alloyed steels. The further characterization of the investigated alloys consisted of soft turning and hard grinding tests, of stress-strain tests, fatigue tests, and bearing tests with ball bearings type 6206. The results of the turning and grinding tests showed no significant influence of the alloying elements up to 1.5 % silicon and 1.1 % manganese. The parameters of the stress-strain curves showed a small influence of the silicon content, which is dominated by the influence of the heat treatment parameters. The change in the retained austenite content and therewith in the mechanical properties due to different tempering procedures is characteristically reduced with the high silicon content of 1.5 %.