Effect of Heat Treatment on the Susceptibility to Stress Corrosion Cracking of Alloy 600

It was shown that a modified Huey test, i.e., a 24-h immersion in boiling 40% HNO3, is able to exactly detect the susceptibility to intergranular corrosion of Alloy 600, which is correlated with intergranular stress corrosion cracking (IGSCC) behavior in high temperature water containing small amounts of chloride ions. Chromium content at the regions adjacent to grain boundaries in sensitized Alloy 600 was analyzed as ~3% by the measurement of magnetic susceptibility.Heat treating Alloy 600 at low temperatures, e.g., at 700°C for 15 h, improves the IGSCC resistance to both high temperature water and caustic solutions by constructing suitable microstructures resistant to sensitization, in which chromium carbides precipitate predominantly in the matrix instead of grain boundaries.