Construction of a physical model and numerical analysis were carried out concerning hydrogen diffusion in solid under elastic-plastic local stress field with hydrogen emission around the crack tip due to the dissolvent anodic reaction. These analyses showed that hydrogen diffuses and concentrates at the site of the elastic-plastic boundary in the direction of crack length when several mechanical conditions are satisfied. Hydrogen accumulation becomes much more remarkable with increase of yield stress. The effect of the diffusion constant is found to correspond to the rate of hydrogen diffusion. It accelerates the rate of increase of hydrogen accumulation at the elastic-plastic boundary, although the maximum saturated value of the concentration is not affected. This analysis shows that a high strength steel is liable to cause the microcrack initiation and coalescence with the main crack due to the hydrogen accumulation and embrittlement at the elastic-plastic boundary. This gives the theoretical foundation to the mechanism on the stress corrosion cracking accompanied with subcritical crack growth for high strength steels.
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