Study on Rolling Contact Fatigue in Hydrogen Environment at a Contact Pressure below Basic Static Load Capacity

Abstract

Rolling contact fatigue tests were conducted in hydrogen and air at a contact pressure of 4.1 GPa, below 4.2 GPa, corresponding to the basic static load capacity in rolling contact bearing using the four-ball tester. The lubricating conditions employed were partial and full elastohydrodynamic lubrication (EHL). The results were compared with those at 5.6 GPa above the basic static load capacity in a previous paper (Endo, et al. (1)). Rolling fatigue occurred in hydrogen but did not occur in air regardless of lubricating conditions. In hydrogen, a crack was initiated in the subsurface under partial EHL conditions and at or in the vicinity of the surface under full EHL conditions. On the other hand, at 5.6 GPa, a crack was initiated at the surface under partial EHL conditions and in the subsurface under full EHL conditions. In a hydrogen environment, the fatigue life in a rolling contact was confirmed to be significantly shortened compared with that in air. The decrease in fatigue life and the difference in crack initiating place are ascribed to permeated hydrogen and its extent into the substrate according to lubricating conditions such as the contact pressure, the severity of direct contact, and the absence of oxide film. The results obtained suggest that in a hydrogen environment there is no fatigue limit in a rolling contact, which is thought to exist in air.