Stress corrosion crack growth rate of welded joint used for low-pressure rotor of nuclear turbine in oxygenated pure water at 180 °C

Abstract Stress corrosion cracking (SCC) growth behavior of NiCrMoV steels welded joint of nuclear steam turbine was systematically investigated, which was conducted in pure water with 8 ppm oxygen at 180 °C. Crack growth rate (CGR) was used to evaluate the susceptibility of SCC for WM with fine bainites and HAZ with coarse prior austenite grains, simultaneously the cracking mechanisms for both zones were explored. WM has lower CGR than HAZ under the similar stress intensity factor, showing it had higher resistance to SCC. Oxygen promoted the nucleation and propagation for cracks. The oxygen diffusion zone (ODZ) formed in front of inner oxide layer through continually diffusion of oxygen in grain, and caused the embrittlement and transgranular cracking for WM. However, fine grains in WM could bear crack driving force and reduce stress concentration to increase the resistance for transgranular crack propagation. As for HAZ, the chromium-rich carbides along the prior austenite grain boundaries (PAGBs) accelerated the intergranular oxidation and facilitated the formation of intergranular oxide zone (IOZ). Thus, the crack could easily propagate in PAGB, and lead to higher CGR for the HAZ.