Effect of hydrogen on Mode II fatigue crack behavior of tempered bearing steel and microstructural changes

In order to clarify the effect of hydrogen on Mode II fatigue behavior, fatigue tests on a bearing steel (SAE52100, HV = 748) were conducted. Cyclic torsion both with and without a static axial compressive stress was applied to hydrogen-precharged and uncharged specimens. For both loading cases, fatigue lives were shorter for the hydrogen-precharged specimens than for the uncharged specimens. Mode II and Mode I fatigue crack growth rates in the hydrogen-precharged specimens were higher than those in the uncharged specimens. The density of Mode II fatigue cracks near the end of life (N/Nf = 0.97) was greater in the hydrogen-precharged specimen than in the uncharged specimen. Microstructural changes and an increased density of slip bands were formed only in the hydrogen-precharged specimens. From these observations, it is hypothesized that hydrogen enhances slip deformation and localized slip bands thus increasing the density of cracks in the hydrogen-precharged specimens.