Cyclic cracking behavior of low-alloy pressure vessel steel in simulated BWR water

Fatigue crack initiation and growth behavior of low-alloy pressure vessel steel A533B has been investigated in simulated BWR water. Two distinguished crack morphologies were observed, closely depending on the cyclic strain rate. At a high strain rate, fatigue cracks grew in a tortuous manner. Final failure pre-dominantly resulted from the continuous growth of a single fatigue crack. A rough fracture surface was obtained on which hydrogen-induced cracking features were dominant. At a low strain rate, however, fatigue cracks developed in an entirely straight manner. Final failure was usually caused by the joint development of multi-site fatigue cracks. A flat fracture surface was obtained on which slight crack arrest rather than typical hydrogen-induced cracking feature was found. In addition, apparent acceleration in fatigue crack growth rate was observed in the temperature and strain-rate regions of dynamic strain aging (DSA). Related environmentally assisted cracking (EAC) mechanisms are also discussed.