Loading-Frequency Effects on Fatigue Crack Growth Behavior of a Low Carbon Steel JIS S10C in Hydrogen Gas Environment

In order to clarify the loading-frequency effect on the fatigue crack growth behavior of a low carbon steel JIS S10C in a hydrogen gas environment, fully reversed bending fatigue tests were carried out. The main results are as follows. The loading-frequency effect on the FCG revealed a complex behavior; that is, not only acceleration, but also deceleration even in the same low loading-frequency range. The slight acceleration appears in the low growth rate range in which the ductile fracture mode is predominant. The deceleration appears due to the transition behavior from a quasi-cleavage fracture mode with a higher FCGR to a ductile one with a lower FCGR. This shows that lowering the load frequency does not necessarily lead to an unpredictable fatigue crack growth.