Observation and prediction of 'initiation dominant growth' due to stress corrosion cracking in type 304 stainless steel in high temperature water

To investigate the initiation behavior of stress corrosion cracking (SCC) for sensitized Type 304 stainless steel in high temperature water, a constant load SCC test method combined with in-situ crack observation technique was employed. The in-situ crack observation system allowed us to detect small cracks of at least 0.1mm. The test results showed that a fracture time decreased with an increase in an applied stress. The first cracks were observed at most three hours before the specimen was fractured under all the stress conditions, followed by initiations of many cracks in a short time to fracture. The observed crack growth was 'initiation dominant growth', which is caused by coalescence of multiple cracks rather than by growth of primary crack. The simulation model for a prediction of 'initiation dominant growth' was newly developed using a Monte Carlo method, which was based on damage mechanics and stress analysis around the existing cracks. The simulation could represent the empirical results of changes in the crack distribution and the cumulative number of cracks during the SCC tests. It was concluded, therefore, that the crack initiation process should be considered in simulating the life prediction of the material in this SCC system. (author)