Stress Corrosion Cracking of Candidate Structural Materials in Simulated First-Wall/Aqueous Coolant Environments

Susceptibility of Types 316NG, 316, and 304 stainless steels (SS) to stress corrosion cracking was investigated in slow-strain-rate tests (SSRTs) in oxygenated water that simulates important parameters anticipated in first-wall/blanket systems. The water chemistry was based on a computer code that yielded the nominal concentrations of radiolytic species produced in an aqueous environment under conditions expected in the International Thermonuclear Experimental Reactor (ITER). Actual SSRTs were performed in a less benign, more oxidizing reference environment at temperatures of 52 to 150°C. Predominantly ductile fracture was observed in Type 316NG and nonsensitized Types 316 and 304 SS SSRT specimens that were strained to failure in a reference ITER water chemistry. The failure behavior of Type 304 SS specimens, heat-treated to yield sensitization values of 2, 3, and 20 Coulomb (C)/cm² by the electrochemical potentiokinetic reactivation technique, demonstrated that the degree of sensitization dramatically affected susceptibility to intergranular stress corrosion cracking. Ranking for resistance to stress corrosion cracking in simulated ITER water by electron microscopy and SSRT parameters, i.e., failure time, ultimate strength, total elongation, and stress ratio, is 304 SS (EPR = 20<2 C/cm²)<316NG SS.