Abstract
Slow strain rate tests (SSRT) and fatigue tests were conducted to investigate the influence of internal hydrogen state on the quasi static SSRT strength and fatigue strength for cold drawn eutectoid steel specimens which were cathodically hydrogen charged. Internal hydrogen states were changed as follows: (a) non-charged sample, (b) the sample that contained both diffusive and non-diffusive hydrogen, and (c) the one that contained only non-diffusive hydrogen. The results of SSRT indicated that only the diffusive hydrogen caused hydrogen embrittlement under the quasi-static loading condition. S-N curves had a large scatter and the influence of non-diffusive hydrogen on the fatigue strength was unclear, because the fatigue crack was initiated at internal inclusion. Therefore, the fatigue strength was discussed based on the stress intensity factor, ΔK_<inc>, calculated from stress and inclusion size. ΔK_<inc>, giving the same N_f decreased in the order of the non-charged specimen, only non-diffusive hydrogen charged specimen and the specimen having both diffusive and non-diffusive hydrogen, indicating that non-diffusive hydrogen caused a decrease in fatigue strength.
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