Stress Corrosion Cracking of Steel in High Temperature Water

In an attempt to elucidate the mechanism of cracking for reactor pressure vessel (RPV) steels in high temperature water, slow strain rate tests (SSRTs) and polarization measurements have been conducted on a series of FeCMnX alloys, where X was either Cr, Ni, Mo, or Si (typical alloying elements for RPV steels) and on some relevant commercial alloys. The SSRTs were performed in 250 C water at a series of applied potentials. On the criterion of the minimum potential at which cracking will occur, nickel and chromium retard cracking, whereas molybdenum enhances cracking. The mechanism of cracking is discussed in terms of the maximum crack velocities observed and typical anodic current densities (CDs) observed in polarization studies. The existing data suggests that the rate controlling mechanism for cracking is anodic dissolution at the crack tip, but that the observed crack growth rates might only be explained by the involvement of a significant contribution from mechanical tearing in the fracture process.