Environmental Variables in the Low Temperature Stress Corrosion Cracking of Inconel 600

The low temperature stress corrosion cracking of sensitized Inconel 600 has been examined using aerated 1.3% boric acid solutions with small additions of sodium thiosulfate. Cracking is observed for thiosulfate concentrations above 10−6 M. The rate of cracking increases with temperature to at least 80 C. Concentrated solutions with potential control give crack velocities up to about 0.4 μm/s at 22 C. Provided that cracks are initiated by slow straining, they continue to propagate at very low apparent stress intensities. Lithium hydroxide additions inhibit SCC by producing borate anions; the rate of borate to thiosulfate ion concentration is an important factor in determining immunity to SCC.