Crack branching behavior and amorphous film formation mechanism during SCC expanding test for multi-layers weld metal of NiCrMoV steels

Multi-layer weld metal of NiCrMoV steels used in nuclear rotor was adopted to perform stress corrosion cracking (SCC) test at 180 celcius, which indicated the crack growth rate in 3.5% NaCl solution was lower than that in pure water. The results obtained from high resolution transmission electron microscopy (HRTEM) analysis revealed that the combined effect of crack branching behavior and amorphous film made contributions to the slower crack growth rate. The aggressive Cl- ions invaded grain in multi-directions that was promoted by dislocation motion, facilitating the main crack to bifurcate. Besides, nanocrystals also enhanced branching behavior by deflecting the crack growth path. An amorphous film forming in crack evolved from the disorder of atom arrangement produced by dislocation accumulation and grew stably with the supplement of carbon atom generated in selective corrosion. The complete amorphous film was absent connected path for migration of aggressive anions, thus weakened the driving force for crack propagation and improved resistance to localized corrosion attack. CO 2022 Published by Elsevier Ltd.

Automated summary

The multi-layer weld metal of NiCrMoV steels used in nuclear rotors was subjected to stress corrosion cracking (SCC) tests, revealing that various factors, such as crack branching behavior and amorphous films, played roles in influencing crack growth rates in different environments.