| To assess the fatigue crack growth behavior of reactor pressure vessel at the nuclear reactor operating condition, the fatigue test was performed under water environments of high temperature and pressure. Test parameters were loading frequency, dissolved oxygen(DO) content and temperature. The results at low DO condition were similar to that in air environment. At high DO condition (8000 ppb), the crack growth rate was increased with the decrease of loading frequency. Fractographic study and surface analysis indicated that the enhancement of crack growth rate was due to environmentally assisted cracks near sulfur inclusions. For the case of 0.05 ㎐ test, crack path was the lath boundaries at low ΔK, while at high ΔK there was brittle facets around carbides. These features were coincident to hydrogen embrittlement. And it is understood crack growth rate depended on the quantities of absorbed hydrogen and also on the number of trapping sites at the plastic flow zone of crack. Especially, the dependence of crack growth rate on ΔK was particularly high in the case of 0.05 ㎐ condition, this may be enhanced by the dynamic strain aging which increases hydrogen trapping sites. |
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