Role of Carbides in Stress Corrosion Cracking Resistance of Alloy 600 and Controlled-Purity Ni-16% Cr-9% Fe in Primary Water at 360°C

Abstract

Abstract Intergranular stress corrosion cracking (IGSCC) of two commercial alloy 600 (UNS N06600) conditions (heat-treated at low temperature [600LT] and at high temperature [600HT]) and two controlled-purity Ni-16% Cr-9% Fe alloys (carbondoped mill-annealed [CDMA] and carbon-doped thermally treated [CDTT]) were investigated using constant extension rate tensile (CERT) tests in primary water (0.001 M lithium hydroxide [LiOH] + 0.01 M boric acid [H3BO3]) with 1 bar (100 kPa) hydrogen overpressure at 360°C and 320°C. Heat treatments produced two types of microstructures in the commercial and controlled-purity alloys: one dominated by grain-boundary carbides (600HT and CDTT) and one dominated by intragranular carbides (600LT and CDMA). CERT tests were conducted over a range of strain rates and at two temperatures with interruptions at specific strains to determine the crack depth distributions. Results showed IGSCC was the dominant failure mode in all samples. For the commercial alloy and controlled-purity a...