Volume 7, Issue 2 (February 2010)
The Role of Hydrogen on Rolling Contact Fatigue Response of Rolling Element Bearings
It is generally accepted that the rolling contact fatigue (RCF) life of bearing components is strongly reduced when the hardened steel matrix contains hydrogen. Although frequently reported in the literature, a physically sound explanation to this phenomenon has not yet been presented. In recent work on building understanding around the nature of the RCF damage process, we have reported on the development of a physically based fatigue damage model. Here we discuss an attempt to interpret the role of hydrogen on the micro-plastic fatigue damage mechanism on the basis of this concept. In this context, the role of hydrogen on the RCF response has been studied in order to find evidence for and to determine its weakening effect on hardened and low-temperature tempered (bearing) steels. In order to perform valid tests, effort was put in controlling the hydrogen content in bearing components before testing using an electrochemical hydrogen charging process. A number of bearing tests were performed clearly showing differences in fatigue response with different amounts of hydrogen present in the microstructure. The results of testing of bearings with hydrogen-containing steel matrices are given. It was found that increased hydrogen content in bearing steel at 5 ppm (by weight) will significantly promote bearing spalling failure and enhance the formation and growth of so-called white-etching crack systems. This experimental information is interpreted in the light of the physically based fatigue damage model.