Effect of Grain Boundary Carbides and Cold Work on Stress Corrosion Cracking of Alloy 600

The stress corrosion cracking (SCC) behavior of alloy 600 in simulated pressurized water reactor (PWR) high-temperature water environment was investigated by direct current potential drop (DCPD) on-line monitoring. Analytical electron microscopy was utilized to characterize the cracking process to better understand the cold work and grain boundary (GB) carbides effect. Synergistic effect of GB carbides and cold work on SCC behavior was identified. A beneficial effect of carbides was identified in non-cold worked alloy 600, which was attributed to the physical impediment and reduced GB internal oxidation. In cold worked alloy 600, GB carbides had a detrimental effect due to the combination of the enhanced local strain at GBs and also enhanced GB internal oxidation.