Abstract
The effect of dissolved oxygen, the main factor in SCC of stainless steel in high temperature water, was studied by CERT, and an analysis of the surface film, and by developing potential-pH diagrams. Under a strain rate of 6.67×10-7sec-1 in 290°C water, IGSCC occured with more than 0.2ppm dissolved oxygen, while TGSCC occured with less than 20ppb dissolved oxygen. When the strain rate increased from 6.67×10-7sec-1 to 3.33×10-6sec-1, the IGSCC susceptibility decreased, but the TGSCC susceptibility remained unchanged. IGSCC was accelerated with increasing dissolved oxygen concentration. The increase in oxygen concentration may bring the corrosion potential of stainless steel closer to the transpassive region where the dissolution of chromium is promoted, and SCC more easily takes place. When the concentration of dissolved oxygen is extremely low, the corrosion potential may shift to the active region, thereby rendering the oxidized film unstable and giving rise to TGSCC.
