Compensation of SAE52100 Bearing Ring Distortion During Gas Nozzle Field Quenching

During hardening of bearing rings, roundness deviations can occur due to either release of intrinsically stored distortion potential or process-related distortion. By deliberately asymmetrical quenching in a gas nozzle field, these deviations - plus original distortion from prior production steps - can be compensated for at least partially. The compensating heat treatment on rings of SAE52100 was investigated in a series of experiments using a dedicated semi-automated heat treatment facility for asymmetrical heating and quenching with high reproducibility. The rings were austenitized at 870 °C for 20 min. After the compensating quenching in the gas nozzle field, they were chilled at 0 °C for 15 min and finally annealed at 180 °C for 2 h. With this procedure it was possible to reduce the roundness deviations of the rings by more than 50 % to an average value of 68 µm as compared to conventional uniform quenching. The observable roundness deviations can be characterized on one hand by identifying basic distortion patterns (Fourier orders) and by distinguishing constant, proportional, and stochastic distortion terms on the other hand. If the analysis is carried out in complex number space, the roundness deviations can be described largely by a multi-linear regression model. Particularly the deviations in the third Fourier order (triangularity) can be predicted very accurately. An impairment of the prediction quality is introduced by non-linear dependencies between the local distributions of gas flux, heat transfer coefficient, and resulting radius deviation as well as by interactions between distortions in different Fourier orders.