Fatigue crack growth behavior of reactor pressure vessel steels in air and high-temperature water environments

Fatigue tests under constant amplitude load were conducted on CT specimens of A533B3 steels with four levels of sulfur content at different temperatures in air and high-temperature water environments. A modified capacitance-type COD gauge was shown to be suitable for fatigue crack length measurement at high temperatures in air. The observation that the Young's moduli measured at a strain rate of 4 x 10-3 s-1 for the A533B3 steels at 150 deg. C and 300 deg. C did not decrease with an increase in temperature seemed to be related to the presence of dynamic strain aging. The fatigue crack growth rates at 150 deg. C and 300 deg. C in air were about two and half times slower than those tested at 400 deg. C, because dynamic strain aging prevailed at 150 deg. C and 300 deg. C. Fractographic examination results suggested that inclusions embedded in secondary cracks enhanced the fatigue crack initiation rather than the fatigue crack growth. The fatigue crack growth rates taken in the oxygen-saturated water environment were one order of magnitude faster than those obtained in air