Abstract
Fatigue crack growth tests were conducted on hydrogen charged and uncharged specimens of a 0.08 mass%C low carbon steel sheet at test frequency 0.001 -10Hz. After fatigue crack growth tests, a stretch zone was formed in order to investigate the mechanisms of fatigue crack growth in the hydrogen environment. From the observation of striation and stretch zone on the fracture surface and slip bands on the specimen surface, it was revealed that uncharged specimens have no dependency of crack growth rate on test frequency and on the other hand, the crack growth rate of hydrogen charged specimens at the lower test frequency is approximately 10 times faster than that of uncharged specimens. There exists an upper limit of the increase in crack growth rate of the hydrogen charged specimens at test frequency below 0.01 Hz. The upper limit is almost equal to the maximum of stretch zone width which is inclined. The experimental results show that the fatigue crack growth of hydrogen charged specimen is related to the hydrogen enhanced localized plasticity.
