Pitting Corrosion and Stress Corrosion Cracking around Heat Affected Zone in Welded Joint of CrNiMoV Rotor Steel in Chloridized High Temperature Water

Abstract

Pitting corrosion and stress corrosion cracking around heat affected zone of 25Cr2Ni2MoV rotor steel welded joint in chloridized high temperature water were studied by using U-bend specimen exposure test and electrochemical test. Different corrosion potentials were detected in various zones of welded joint with the order: heat affected zone > base metal > weld metal. By contrast, a reversed order was observed for pit density in welded joint which was partly ascribed to the galvanic effect of different zones. Stress corrosion cracks initiated from pits preferentially at the fusion line was observed because of its most complicated microstructure and highest hardness. A finite element analysis was carried out to evaluate the plastic strain distribution on the U-bend specimen. A great leap of the plastic strain from the weld to the fusion line could also explain the significant susceptibility to stress corrosion cracking at the fusion line.