Role of Oxide Film in Intergranular Stress Corrosion Cracking of Sensitized Type 304 Stainless Steel in High Temperature Water

Intergranular stress corrosion cracking (IGSCC) of sensitized Type 304 stainless steel in high temperature water was investigated in relation to the nature of oxide film. SCC tests were conducted in 0.2 to 32 ppm oxygen water at temperatures of 523 and 563 K, under two-step loading conditions; a slow strain rate technique (SSRT) up to a stress level of 275 MPa and followed by a constant loading test.IGSCC failure time was decreased with increasing dissolved oxygen (DO) concentration from 0.2 to 8 ppm oxygen, and lengthened at 16 ppm oxygen and again shortened at 32 ppm oxygen. Auger electron spectroscopic analysis indicated that a chromium-rich oxide was formed in an inner oxide film on the specimen surface exposed to water containing 0.2 ppm oxygen, and no chromium-rich oxide was formed on the specimen surface exposed to water containing above 2 ppm oxygen.The low susceptibility to IGSCC of sensitized Type 304 stainless steel in water containing 0.2 ppm oxygen may be correlated with the formation of chromium-rich oxide film. It was confirmed that crack initiation is stifled by the formation of chromium-rich oxide film on the specimen surface. Furthermore, the role of oxide film in IGSCC is discussed in relation to the anodic dissolution behavior and physical properties such as electric resistance, structure and porosity of oxide film.