Microstructural insights into effects of pressurized water reactor environment and cyclic loading parameters on the low cycle fatigue behavior of 316L stainless steel

Austenitic stainless steels, commonly used in light water reactor coolant environments, can be susceptible to environmentally assisted fatigue due to non-monotonic loading conditions, primarily associated with load-follow operations, thermal transients, or intermittent plant shutdowns and start-ups. The effects of a pressurized water reactor (PWR) environment containing hydrogen and cyclic loading parameters on the low cycle fatigue (LCF) behavior of 316L stainless steel were investigated by comprehensive striation spacing evaluation and advanced microscopic characterizations. The exposure to a PWR environment results in a decreased LCF lifetime, an enhanced fatigue crack initiation and an accelerated fatigue crack growth rate of 316L austenitic stainless steel. The interaction between hydrogen and localized deformation contributes to the observed acceleration of fatigue crack growth rate in a PWR environment. The evaluation of the effect of waveform (periodic underload PUL, periodic overload POL and constant amplitude sawtooth CA) shows that both PUL and POL reduce the low cycle fatigue lifetime, accelerate the fatigue crack growth rate and advance the cycle where fatigue crack initiation occurs compared to CA loading. LCF waveform strongly influences the shear band formation, localization of plastic deformation and stress state.