Intergranular Stress Corrosion Cracking of Platinum Treated Type 304 Stainless Steels in High Temperature Water

Abstract

Electrochemical polarization analyses, slow strain rate tensile (SSRT) tests and crack growth tests were conducted to investigate the intergranular stress corrosion cracking (IGSCC) characteristics of platinum treated Type 304 stainless steels in 288°C pure water. All specimens were thermally sensitized and pre-oxidized before the tests, and some of them were additionally treated with platinum via hydrothermal deposition. Test environments were specifically designed in a circulation loop to create water chemistry conditions of hydrogen to oxygen molar ratios (MH/O)of 0, 0.5, and 2.7 in the coolant. Test results showed that the corrosion current densities of the specimens treated with platinum were higher than those of the pre-oxidized ones under oxygenated conditions, but the corrosion potentials of the treated specimens could be either lower or higher than those of the untreated ones. In addition, IGSCC was not observed on all specimens (treated or untreated) when the MH/O in the test coolant was 0.5 or 2.7. However, the platinum treated specimens actually showed severer IGSCC after the SSRT tests conducted under the coolant condition of MH/O=0. Crack growth test results indicate a similar but worse trend to that in the SSRT tests. It was therefore suggested that one must exercise extra caution to use corrosion potential as a sole indicator in evaluating the influence of noble metal treatment on the IGSCC susceptibility of Type 304 stainless steels, especially when the MH/O in the coolant is relatively low or the dissolved oxygen concentration remains comparatively high.