Analysis of initiation and propagation of stress corrosion cracks in sensitized type 304 stainless steel in high-temperature water

A slow strain rate testing apparatus equipped with an autoclave as well as with an in-situ crack observation system has been newly developed. Using this system, the growth behavior of multiple cracks in high-temperature water up to about 300 degreesC could be observed in-situ. In this study, the initiation and propagation of stress corrosion cracks in sensitized Type 304 (UNS S30400) stainless steel immersed in 10(-4) kmol/ m(3) sodium sulfate (Na2SO4) solution from 100 degreesC to 250 degreesC were investigated. It was found that stress corrosion cracking (SCC) susceptibility evaluated from the time to fracture increased with an increase in temperature. The in-situ observations of the cracks revealed the following: -The time to initiate the first crack decreased with art increase in temperature. -The cumulative number of cracks increased almost linearly with deformation time at any temperature. -Both the final number of cracks and the crack initiation frequency exhibited a maximum at 150 degreesC. -The distribution in the crack propagation rates was found to fit the Weibull probability distribution. The mean crack propagation rate increased with an increase in temperature according to the Arrhenius relation with an estimated activation energy of about 2.1 kcal/mol.