Rolling Contact and Compression-Torsion Fatigue of 52100 Steel with Special Regard to Carbide Distribution

摘要

In the past, many successful efforts have been made to increase the lifetime of bearings by reducing the amount of the nonmetallic inclusions in bearing steels. As a result of these efforts, other microstructural discontinuities like coarser carbides get into focus, which possibly also reduce bearing life. In this work, eight processing variants of steel 52100 were examined. The steels were of high purity and differed in their manufacturing route. Especially the influence of carbide stringers on the rolling contact fatigue behavior of cylindrical roller bearings was examined. Finite element calculations of different microstructural carbide configurations were carried out. They showed that carbides lead to a significant increase of micro-stresses and therefore are supposed to reduce the bearing life. Nevertheless, experiments and calculations showed if oxides are still present they have a dominant influence on the bearing lifetime. In some of the examined steel variants an increased amount of remaining oxides was detected in the area where carbide stringers occur and the rolling contact fatigue life could be correlated with the local content of oxidic inclusions. Additionally to the determination of fatigue life curves of bearings with a common rolling contact fatigue test rig, an alternative test method was tried using cylindrical specimens and a servo-hydraulic testing machine. The specimens were loaded by combined in-phase compression and torsion in that way that a similar relation of the principal stresses as in the Hertzian contact was generated. A successful fatigue life correlation between the specimens' lifetimes and the results from the bearing tests was possible using the damage calculation after Miner and Crossland's fatigue criterion.