The Role of Hydrogen on Rolling Contact Fatigue Response of Rolling Element Bearings

Abstract

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.

Thermal Desorption Analysis of Hydrogen in Non-hydrogen-Charged Rolling Contact Fatigue-Tested 100Cr6 Steel

“…near surface), nor locally where hydrogen is attracted at traps such as crack tips [28,60], areas of plastic deformation and inclusions [14]. It is likely the concentration at these locations will be higher due to hydrogen being attracted and trapped at these sites [28,29,60].…”

“…It is, however, noted that trapping and saturation of cracks with hydrogen could eventually lead to an internal pressure buildup stimulating crack growth. A counter-argument to this is that saturation of the crack could alleviate the ability for crack face rubbing/beating to occur during RCF [28], where crack rubbing/beating is proposed to generate WEAs [28,29]. It is suggested that in the formation process of WEAs, hydrogen serves only to enhance brittle cracking, forcing cracks open and inducing additional crack rubbing/beating [28].…”

“…gas chromatography (GC) or hot carrier gas extraction [32]), TDA coupled with a mass spectrometer (TDMS) [10,14,29,33,34] and secondary ion mass spectrometry (SIMS), used to measure the local concentration of hydrogen in specimens and at defects such as inclusions [35,36]. The primary method for measuring hydrogen in weld steels under the BS ISO 3690 [32] has been the mercury method; however, due to the health hazards when using mercury and the long analysis times involved other methods for measuring hydrogen have been exploited.…”

“…TDA is one of the more popular methods, where negligible differences in measurable hydrogen concentrations between TDA methods and the primary mercury methods have been found [37,38], and thus TDA methods are consequently recognised in the BS ISO 3690 [32] for measuring hydrogen in steel welds. Consequently, TDA has been used to measure the concentration of diffusible hydrogen in bearing steels in a number of studies [10,17,28,29,33,[39][40][41][42].…”

“…Many previous investigations have concentrated on the analysis of pre-hydrogen-charged RCF test specimens [4,6,29,33,39,41,[47][48][49][50][51][52], where it is generally noted that pre-charging decreases RCF life in bearing steels that fail from WSF. This study uses TDA to measure the concentration of diffusible hydrogen in nonhydrogen-charged specimens to better simulate the environments experienced in service.…”