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The damage mechanisms of antifriction bearings operating under debris contaminated lubrication have been investigated experimentally. A particular experimental procedure has been designed to simulate natural foreign particle indentations and to allow a quick reproducible fatigue test comparison on material and heat treatment variants. Additionally, the scattering of the fatigue test results could be reduced significantly.
The different phases of the damaging process are described. From these results measures have been derived to increase the bearing performance and lifetime under these stress conditions, which are governed by geometrical notch effects and localized metal-to-metal-contact and plastic deformation. The effectiveness in laboratory tests has been checked versus field applications.
An optimization of the materials microstructure was found to be an efficient means to counteract such problems. This was done by modifying the alloying content of the bearing steel and the surface composition respectively and changing the heat treatment in a way to generate a certain amount of very stable retained austenite. This particular microstructural component could be proved to have inherent self-healing capabilities against indentations produced by the overrolling of debris particles and the subsequent reflattening of the raised edges around the dents. This effect can be demonstrated by base-alloying of through-hardening grades as well as by surface alloying of case-hardenable steels.
The actual amount and the stability of the retained austenite against mechanical or thermal-induced transformation are important properties to achieve the tolerance to dent effects. Results of laboratory fatigue tests of different development routes and field experiences are presented. The consequences of these measures on the dimensional stability of the bearings are explained.
rolling contact fatigue, contaminated lubrication, bearing performance, material optimization, heat treatment optimization
Material scientist, FAG Industrial Bearings AG, Schweinfurt,
Material research and development, FAG Industrial Bearings AG, Schweinfurt,