Environmentally Enhanced Fatigue Crack Growth of a High-strength Steel Sensitive to Stress Corrosion Cracking

概要

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Low-cycle fatigue tests and sustained load tests of a high-strength steel (SNCM8) sensitive to stress corrosion cracking (SCC) have been carried out under various hydrogen contents. The threshold stress intensity facto for cyclic SCC under cyclic stress K_<FSCC> is smaller than the threshold value for static SCC under sustained load K_<ISCC>, K_<FSCC> being smaller with an increasing hydrogen content. In a steel tempered from a low temperature no hydrogen embrittlement is caused until diffused hydrogen is concentrated into a plastic zone at crack tips under small hydrogen content, so that the influence of stress waveforms becomes identical with that in a usual corrosion fatigue. Under high hydrogen content cyclic SCC plays a predominant role and a holding period during one cycle most enhances the crack growth. In a steel tempered from a high temperature the corrosion fatigue crack growth characteristics are the same as those in a usual low-strength tough material.
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