Effects of humidity on crack initiation mechanism and associated S–N characteristics in very high strength steels

Super-long life fatigue tests were first conducted on Ni–Cr–Mo steel in laboratory air, dry air and distilled water and then performed on high C–Cr bearing steel in controlled humidity for a further understanding of the effect of humidity level. It was indicated that humidity exerted a significant influence on the crack initiation mechanism and associated S–N characteristics in both steels. Based on the experimental results and fractographic analyses of fracture surfaces, the effect of humidity on fatigue life, the humidity dependence of the conventional fatigue limit, the subsurface fracture process, and the presence of the intrinsic fatigue limit are discussed.