INITIATION AND GROWTH OF STRESS-CORROSION CRACKS IN TYPE 316L STAINLESS-STEEL DURING SLOW STRAIN-RATE TESTING

The initiation and growth of cracks in type 316L (UNS S31603) stainles s steel (SS) in a chloride solution containing thiosulfate ions (S2O32 -) during slow strain rate testing (SSRT) were analyzed on the basis o f fracture mechanics. Crack behavior on the specimen surface was obser ved in situ using a charge-coupled device (CCD) camera with a videotap e recording system. Three types of specimens were used: a single-notch ed plate, a smooth cylinder, and a smooth plate. The single-notched sp ecimen failed to produce a sharp crack similar to that formed on the s mooth specimens. For the smooth specimens, the stress intensify factor (K-ISCC) was found to vary from 3.9 MN/m(3/2) to 5.0 MN/m(3/2), and t he crack growth rate ranged from 5.2 x 10(-9) m/s to 1.0 x 10(-8) m/s, which approximately agreed with data determined by other authors usin g a fracture mechanics approach. Thus, the SSRT combined with the in s itu observation technique was useful in analyzing the crack initiation and growth process.