Published: Oct 2012
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Rotating bending tests have been performed on bearing steel samples with varied metallurgical cleanliness and hot forming deformation levels. The samples were tested under constant applied stress, as well as by staircase testing, in order to derive a fatigue limit estimate. Ball and roller bearing rings machined from the same raw materials were subjected to rolling contact tests. Results obtained in rotating beam testing can be problematic in terms of their interpretation. The drastic reduction in life with increased stress is masked by the conventional logarithmic (or even double logarithmic) scales always used, and this leads to an unfounded discussion of the existence of a “fatigue limit” for hardened steels. There is no doubt that there is a very drastic drop in fatigue resistance with increased stress levels in hardened bearing steels, and that there also exists an “engineering” fatigue limit for such components. In direct comparisons, rotating beam tests provide relative life estimates for metallurgically different variants that relate well to rolling contact fatigue tests in which sub-surface induced fatigue is the dominating failure mechanism. Rotating beam fatigue testing also provides very valuable information about the initiation mechanisms, the harmfulness of different inclusion types, and the fracture mechanical properties of the materials tested.
bearing steel, steel making, hot forming reduction, nonmetallic inclusions, fatigue
Development Engineer, AB SKF, Gothenburg,
Lund, Thore B.
Project Manager, AB SKF, Gothenburg,