Stress corrosion cracking of alloy 600 in an aqueous solution containing lead oxide

The stress corrosion cracking (SCC) behavior of Alloy 600 was studied in aqueous solutions containing lead. Electrochemical polarization and current transient experiments were performed at 315 °C in a 40% sodium hydroxide solution to assess the effect of lead on a passive film formed on Alloy 600. The influences of the alloy microstructure and the addition of an inhibitor to the environments on lead-induced SCC were investigated using C-ring and slow strain-rate tensile (SSRT) tests in demineralized high-purity water and caustic solutions containing PbO at 315 °C. The surface films on Alloy 600 were examined using Auger electron spectroscopy (AES) and energy dispersive x-ray spectroscopy (EDXS). The PbO markedly accelerated SCC of Alloy 600 in the caustic solution and the high-purity water at 315 °C. The addition of nickel boride (NiB) or cerium boride (CeB6) to the test solutions decreased the susceptibility of Alloy 600 to SCC. Thermally treated Alloy 600 (Alloy 600 TT) tended to crack in a transgranular mode, while the solution-annealed Alloy 600 (Alloy 600 SA) tended to crack in an intergranular mode in water containing PbO.