Improved stress corrosion performance for alloy 718 via melt practice and heat treatment variation

Alloy 718 is increasingly used in light water reactors for core internals requiring high strength, relaxation resistance, and corrosion resistance. Typical PWR primary-side applications include bolts and springs. Stress corrosion cracking (SCC) tests were conducted using alloy 718 in various melt practice and heat treatment conditions. Fatigue-precracked, 12.5-mm-thick compact fracture specimens were subjected to a constant extension rate of 1.3 x 10-9 m/s in a 360 C buffered aqueous environment. Crack growth rate was measured during testing using a reversing DC potential drop technique. Results in the form of SCC crack growth rate versus applied stress intensity demonstrate that the SCC resistance of alloy 718 can be improved by changes in melt practice and heat treatment. The SCC resistance of electroslag remelted (ESR) material is optimized by applying a high-temperature solution anneal followed by aging below the temperature region in which δ precipitates