Effect of Hydrogen on Very High Cycle Fatigue Behavior of a Low-strength Cr-Ni-Mo-V Steel Containing Micro-defects

The role of hydrogen in fatigue failure of low strength steels is not as well understood as of high strength steels in very high cycle fatigue regime. In this work, axially cyclic tests on a low strength Cr-Ni-Mo-V steel with charged hydrogen were carried out up to the very high cycle fatigue regime under ultrasonic frequency to examine the degradation of fatigue strength and associated failure mechanisms. Results show that the S-N curves show a continuously decreasing mode and hydrogen-charged specimens have lower fatigue strength and shorter fatigue lifetime, as compared with as-received specimens. It is concluded that the hydrogen trapped by inclusions drives interior micro-defects as dominant crack initiation site, and has a clear link to the initiation and early growth of interior fatigue cracks.