Effect of Processing Variables on the Caustic Stress Corrosion Resistance of Inconel Alloy 600

It has been shown that a thermal treatment in the carbide precipitation regime significantly improves the caustic stress corrosion cracking (SCC) resistance of Inconel Alloy 600. The effect of processing history on the response to thermal treatment (704 C/15 hours) has been studied in four heats of Inconel Alloy 600 steam generator tubing. It was possible to introduce a wide range of grain boundary microstructures by varying the furnace parameters used in the final mill anneal. In all instances, thermally treated material had superior SCC resistance to the mill annealed product in deaerated 10% sodium hydroxide at 315 C (600 F). The test was not severe enough to detect any differences in SCC behavior due to the different processing histories. However, there was a heat to heat variability in the SCC resistance of mill annealed Inconel Alloy 600. Thermally treated tubing was found to have superior SCC resistance to mill annealed material in the stress range 17,000 to 40,000 psi in deaerated 10% sodium hydroxide at 315 C (600 F).