Strain Rate Effects on the Fatigue Crack Growth of SA508 Cl.3 Reactor Pressure Vessel Steel in High-Temperature Water Environment

Corrosion fatigue tests were performed in air saturated hot water to assess fatigue crack growth behavior of reactor pressure vessel steel at the LWR operating condition. The main test parameter was loading frequency. Crack growth rate was increased with decreasing frequency until a critical frequency. It was found through fractographic study that the enhancement of crack growth rate was environmentally assisted by the hydrogen embrittlement, since brittle striations and cleavagelike facets with microvoid were formed in the crack growth process. The strain rate effects on crack growth rate were investigated through $da/dt$ versus $dε/dt$ curves. At intermediate range, there is a transient point which corresponds to an onset of dynamic strain aging and abruptly increases the crack growth rate; above the transient point, small-size-particle-enhanced brittle cracks, while only large-size-particle-enhanced brittle cracks before the transient. From the fractography, it is suggested that EAC may be enhanced by specific strain rate, and that EAC may be related to interactions of hydrogen with oxide film and to Luders band movement with a high strain gradient at inclusion/matrix interface.