Insight into corrosion fatigue initiation and cracking mechanism of E690 steel in SO_2-polluted marine atmosphere

摘要

E690 steel is now the leading high strength low alloy steel used in marine engineering constructionin China. Our previous research indicated that this kind of steel has a tendency of intergranularcorrosion along prior austenite grain boundaries and is highly susceptible to stress corrosioncracking (SCC) in SO_2-polluted marine atmosphere. However, the mechanism of intergranularcorrosion and crack initiation has not been fully understood yet. Therefore, in this work we areinterested in the corrosion fatigue behaviors of E690 steel in this environment and aims to lookinsight into the mechanism of corrosion fatigue initiation and cracking of E690 steel under lowfatigue loading. Results showed that it has a very low fatigue life in this environment, i.e. it ishighly susceptible to corrosion fatigue in this environment. Corrosion fatigue cracks initiated mostlyfrom prior austenite grain boundaries (PAGBs) and propagated in a mixed mode of intergranularand transgranular. Microcracks initiated along PAGBs after 24 hours of corrosion fatigue test atpeak stress of 0.8 σ_s. Based on TEM and SKPFM measurements, it was revealed the blocky M-Aconstitutes along PAGBs induced the intergranular corrosion and crack initiation due tomicrogalvanic effect, while the nanoscale rod-like M-A constitutes along ferrite lath boundaries didnot result in crack initiation.