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) stainless steel (SS) in a chloride solution containing thiosulfate ions (S2O32-) during slow strain rate testing (SSRT) were analyzed on the basis of fracture mechanics. Crack behavior on the specimen surface was observed in situ using a charge-coupled device (CCD) camera with a videotape recording system. Three types of specimens were used: a single-notched plate, a smooth cylinder, and a smooth plate. The single-notched specimen failed to produce a sharp crack similar to that formed on the smooth 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 the 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 using a fracture mechanics approach. Thus, the SSRT combined with the in situ observation technique was useful in analyzing the crack initiation and growth process.