非拡散性水素吸蔵条件下における伸線強加工高強度鋼の疲労き裂進展特性と脱離水素の可視化

概要

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Fatigue crack growth tests were conducted to investigate the influence of irreversible hydrogen on the fatigue crack growth in a cold drawn high strength steel. The fatigue crack growth rate was accelerated by irreversible hydrogen in low ΔK or ΔK_<eff> region, and the acceleration increased with a decrease in ΔK or ΔK_<eff>. Moreover, the fatigue crack growth rate under irreversible hydrogen charging increased as the cyclic frequency decreased. To investigate the behavior of irreversible hydrogen near the crack tip under cyclic loading, a hydrogen microprint technique was applied to the fatigue crack growth tests. After the fatigue crack growth under irreversible hydrogen charging, silver particles precipitated along the fatigue crack: this proved that irreversible hydrogen desorbed out from its trap site under cyclic loading. The precipitation area of silver particles was larger than a monotonic plastic zone. Considering the dependency of stress cyclic frequency on the crack growth rate, it is concluded that the hydrogen desorbed from irreversible trap site due to cyclic loading diffuses to the fatigue crack tip and accelerates the fatigue crack growth rate under irreversible hydrogen charging condition. This is the reason why the fatigue crack growth rate was dependent on stress cyclic frequency.
2010-09-25