A Comparative Study of Stress Corrosion Cracking Of Steam Generator Tube Materials in Water at 315 C

Stress corrosion cracking (SCC) of Type 304 and 304L stainless steels, Inconel 600, Incoley 800, and Monel 400 has been studied in water at 315 C, with or without 0.6 ppm Pb and 0.05 or 8 ppm O₂. In 1600 hours test, results indicated that under mill annealed, cold worked (25%) and stress relieved (675 C, 1 hour) conditions, Type 304L, Incoley 800, and Monel 400 were resistant to cracking, whereas highly stressed Inconel 600 cracked intergranularly, irrespective fo the presence of Pb and O₂ content in the water. Inconel 600, heat treated at 600 C for 24 hours or more following annealing, was found to be resistant to SCC. This beneficial heat treatment at 600 C has resulted in semi-continuous type precipitates at the grain boundaries. In addition, this heat treatment appeared to have stabilized the microstructure of Inconel 600, as seen indirectly, such as from the changes in mechanical properties, hydrogen uptake, and electrochemical behavior. The effects of these microstructural changes on the SCC behavior have been discussed.