Hydrogen penetration in water-accelerated fatigue of rolling surfaces

Abstract

When a steel ball was rolled under load in contact with three similar balls in the presence of a mineral oil containing tritiated water, both tritium and hydrogen were absorbed by the steel surfaces. The amount of absorbed tritium increased with the time of stressing. All the data for the amount of tritium absorbed by the balls fell on a single curve when the time of stressing was represented non-dimensionally by dividing it by the [mean pitting life] corresponding to the experimental conditions. The tritium content decreased by outward diffusion for the first five days after stressing, but thereafter remained constant. The extent to which tritium adsorption sites are occupied appears to control both the outward and inward diffusion processes. Analyses of steel balls for hydrogen showed that the total hydrogen content was greater by a factor of more than 100 than the hydrogen equivalent of the tritium present. This observation can be explained by the penetration of hydrogen produced by cracking of the oil in the presence of water. The observations verify an earlier hypothesis that the acceleration of pitting failure of steel balls by water contamination in mineral-oil lubricants can be explained by hydrogen embrittlement.