Intergranular crack propagation rates in sensitized Type 304 stainless steel in an oxygenated water environment

Abstract

Intergranular stress-corrosion crack (IGSCC) propagation rates were measured in three heats of sensitized Type 304 stainless steel (SS) as a function of sensitization in an environment of high-purity water with 8 ppm oxygen, using a fracture mechanics approach. Specimens were sensitized using controlled furnace heat treatments and the degree of sensitization was measured by the electrochemical potentiokinetic reactivation (EPR) method. Active loading tests were performed on standard specimens over a range of intensities. Crack lengths were determined by compilance measurements using in-situ high-temperature clip gage or LVDT methods, optical metallography on the side faces of the specimen, and fractography of the cracked surface after completion of the tests. The optical metallography measurements did not provide useful estimates of crack lengths, because large variations in IGSCC propagation across the thickness of the specimens occurred. The effects of the degree of sensitization on the IGSCC propagation rate are obscured by the data scatter. However, it seems clear that these variables do not lead to order-of-magnitude changes in the crack propagation rate.