Hydrogen Diffusion in Water-accelerated Rolling Surface Fatigue

Abstract

THE pitting failure of rolling bearings is now generally regarded as a surface fatigue phenomenon, and recent work¹ has shown that the presence of water in mineral oil lubricants can accelerate the failure of ball-bearings manufactured from conventional E.N.31 steel. A possible mechanism for this phenomenon has been suggested by Grunberg and Scott². The hypothesis is that vacancy-induced diffusion of hydrogen into the highly stressed surface material produces ‘hydrogen embrittlement’. To test this theory, four-ball rolling tests^1,2 were carried out with a lubricating oil containing 6 per cent tritiated water of high activity (5 c./ml.). The rolling four-ball test produces a track on the driving ball in which pits are normally formed. The three driven balls are stressed to a lesser extent and usually do not show evidence of surface fatigue. Balls from tests using tritiated water were washed with acetone and partially immersed in a liquid scintillator (0.3 per cent 2,5-diphenyloxazole + 0.01 per cent l,4[2-(5-phenyloxazolyl)]-benzene in toluene) and the activity counted using a (refrigerated) ECKO N612 unit. When the part of driving balls carrying the fatigued track was immersed in the liquid scintillator, counting-rates of between 1,000 and 2,000 counts/sec. were recorded. The unfatigued part of driving balls gave only counts of about 40 counts/sec. against the background count of 30 counts/sec. The activity in the fatigued tracks decreased with time and tended towards the background-level after about five days.