Effect of cathodic polarization on stress corrosion cracking susceptibility of 35CrMo steel for Class 12.9 fasteners in seawater

Abstract

The effect of cathodic polarization on stress corrosion cracking (SCC) of 35CrMo steel for high strength fasteners in seawater was investigated by electrochemical measurement, slow strain rate tensile tests and fracture analyses. The results demonstrated that the 35CrMo steel with a typical tempered martensite microstructure has some SCC susceptibility at the open circuit potential (OCP), and the susceptibility decreases as the potential is shifted negatively until −850 mV vs. SCE, at which the steel presents the lowest SCC susceptibility due to the inhibition of anodic dissolution (AD) and little hydrogen evolution. The SCC sensitivity increases significantly as the applied potential further shifts negatively because of intensive hydrogen evolution. The fractures are transgranular at all potentials. AD is considered to be the main cracking mechanism at OCP, while hydrogen embrittlement becomes dominant at the potential below −850 mV vs. SCE.