Abstract
The mechanism of fatigue failure, in the extremely high cycle regime, is studied on a bearing steel, ASTM A295 52100. Special focus was given to the optically dark area (ODA) in the vicinity of fracture origin (subsurface nonmetallic inclusion) of specimens QT that received the conventional heat treatment and quenching followed by tempering. Specimens having a longer fatigue life had a larger ODA. To investigate the influence of the hydrogen trapped by inclusions on fatigue properties, specimens heat treated in a vacuum (specimens VQ) were prepared. At the identical fatigue life Nf, specimens VQ had a slightly smaller ODA than specimens QT. Hydrogen was detected around the inclusion at fracture origin of both specimens. These results were compared with those for a Cr-Mo steel, SCM435. It can be concluded that the formation of ODA is closely related to hydrogen trapped by nonmetallic inclusions. The mechanism of duplex S-N curve is also discussed.
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