| Stress corrosion cracking of sensitized type 304 stainless steel has been studied in pure water, chloride solutions with and without sulfur species at temperatures from 50 to 200(DEGREES)C using the slow strain rate technique. Pitting corrosion was also studied in the same environment using the potentiostatic method. The stress corrosion cracking tendency shows a special temperature dependency in the presence of sulfur species in air saturated chloride solutions. At temperature below 100(DEGREES)C, the presence of sulfide and thiosulfate ions promotes stress corrosion cracking. At 150(DEGREES)C, sulfide ions inhibit stress corrosion cracking while thiosulfate ions promote it. At 200(DEGREES)C, both anions inhibit stress corrosion cracking. However, stress corrosion cracking does not occur in the sulfide solution in the absence of chloride ions. Even when sulfide and chloride ions are present in the solution simultaneously, the decrease of dissolved oxygen content significantly decreases the susceptibility to SCC. Pitting corrosion shows the same temperature dependency in the temperature range from 50 to 200(DEGREES)C in the solutions containing sulfur species. Sulfide ions form either a protective or non-protective iron-sulfide film, depending on the temperature. At temperatures below 100(DEGREES)C, sulfide ions form a non-protective iron sulfide film and promote SCC and pitting. At temperatures above 150(DEGREES)C, however, they form a protective iron sulfide film and inhibit SCC and pitting. Thiosulfate ions are adsorbed and promote SCC and pitting by activating anodic dissolution and by impeding repassivation. |
