Crack Initiation and Growth Analysis by Direct Optical Observation During SSRT in High Temperature Water

The stress corrosion cracking behavior during the slow strain rate test (SSRT) has been investigated in high temperature water. SSRTs were performed on center-notched thin plate specimens of sensitized Type 304 stainless steel. A direct optical observation system consisting of single crystal sapphire windows was employed to separate the SCC into an initiation and a growth stage, and to measure the crack growth rate. Effects of the extension rate, test temperature, and dissolved oxygen concentration on the crack initiation and growth were examined. The crack growth data were analyzed with different variables, including the elastic plastic fracture mechanics parameters. The best interpretation of the crack growth rates is obtained by plotting them vs the time differential of J-integral, which is an estimate of the crack tip deformation rate during SSRT.