The Influence of Thermal Treatment on the SCC Behavior of Inconel Alloy 600 at Controlled Potentials in 10% Caustic Soda Solutions at 315 C

Electrochemically controlled test methods have been used to determine the influence of thermal treatment on the stress corrosion cracking (SCC) resistance of Inconel alloy 600 (I-600) in deaerated 10% NaOH solutions at 315 C (600 F). Maximum susceptibility to SCC was observed when the electrode potential of the I-600 was held in the potential range corresponding to the active-passive transition region of the anodic polarization curve. In the most susceptible potential range, the crack growth rate was approximately 20 times greater in mill annealed I-600 than in similar material thermally treated at 705 C (1300 F) for 24 hours. The improved resistance to SCC propagation could be correlated with the presence of a semicontinuous grain boundary carbide precipitate and/or segregation of phosphorus to the grain boundaries.