Stress corrosion cracking of candidate structural materials under simulated first-wall/aqueous coolant environments

Stress corrosion cracking (SCC) susceptibility of Types 316NG, 316, and 304 stainless steels (SS) 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 which yielded the nominal concentrations of radiolytic species produced in an aqueous environment under ITER-type conditions. Actual SSRTs were performed in a less benign, more oxidizing reference environment at temperatures from 52 to 150 degree C. Predominantly ductile fracture was observed in Type 316NG and nonsensitized Types 316 SS and 304 SS SSRT specimens 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, or 20 Coulomb (C)/cm2 by the electrochemical potentiokinetic reactivation (EPR) technique, demonstrated that the degree of sensitization had a dramatic effect on intergranular stress corrosion cracking (IGSCC) susceptibility. Ranking for resistance to SCC 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. 11 refs., 6 figs., 7 tabs