Stress Corrosion Cracking Behavior of Alloy 718 Subjected to Various Thermal Mechanical Treatments in Primary Water

Abstract

Alloy 718 is an age hardenable, nickel-base alloy used in fuel assembly of Pressurized Water Reactors (PWRs) by virtue of its high strength and resistance to corrosion and stress corrosion cracking (SCC). SCC susceptibility is affected by the microstructure developed during thermal mechanical treatments. The SCC behavior of alloy 718 in three different thermal mechanical treatments (TMTs) and two different heats was studied in PWR primary water environment using constant extension rate tensile (CERT) tests. TMTs have a significant effect on the microstructure and thus the mechanical behavior and the SCC susceptibility of alloy 718. TMTs using a solution anneal at 1093 °C with a two-step ageing treatment (1093 °C/1 h + 718 °C/8 h + 621 °C/8 h) exhibited the best SCC resistance.