In situ Measurement of Stress Corrosion Crack Tip Properties during Environmentally Induced Cracking in Stainless Steel 304L Available to Purchase

The influence of the external cathodic area, stress intensity, and electrochemical polarization level on the resultant crack growth rate and crack tip pH and potential were studied for stainless steel 304L in a sodium chloride environment. Prior to testing, the validity of in-situ crack tip property measurements using micro-probes and drilled holes was supported through modeling efforts and confirmed with experimental observations. It was found that increasing R-ratio during corrosion fatigue increased crack growth rate and decreased the measured crack tip pH of the 304L sample. Decreasing the electrochemical potential (i.e., cathodic polarization) of the bulk sample increased the crack tip pH and stopped measured crack extension under constant K conditions. Conversely, increasing the potential of the bulk sample decreased the crack tip pH and induced cracking under constant K conditions. Decreasing cathodic area external to the crack increased the measured pH at the crack tip and decreased crack growth rate under fatigue conditions. For the given configuration, environment, and alloy studied, fatigue crack growth is not sustained by cathodic reactions solely occurring in the crack wake and notch. These results have implications on the ability to predict atmospheric crack growth rates from laboratory, full immersion experiments.