Abstract
The initiation and evolution of the localized corrosion in carbon steel were investigated in a simulated marine environment of Xisha Island in the South China Sea. In the initial stage, localized corrosion occurred in the form of corrosion spot. The localized corrosion morphology and electrochemical information during corrosion process were tracked by field emission scanning electron microscopy energy dispersive spectrometry (FE-SEM-EDS), scanning vibrating electrode technique (SVET) and scanning Kelvin probe force microscopy (SKPFM). Localized corrosion was induced by the microcrevices around Al2O3 inclusions. The occluded cells and oxygen concentration cell formed in the pits could accelerate the localized corrosion. Pearlite accelerated the dissolution of the inside and surrounding ferrite via the galvanic effect between Fe3C and ferrite. Overall, the localized corrosion was initiated and evaluated under a synergistic effect of crevice corrosion, occluded cells, oxygen concentration cell and the galvanic couple between FeC3 and ferrite.
Highlights
High strength steels have been used globally for the construction of road installations, electricity posts, utility towers, guide rails, ornamental sculptures and facades and oil and gas pipelines in the marine environment
Inclusions in the steel were analyzed by Field emission scanning electron microscopy (FE-SEM)-energy dispersive spectrometer (EDS) prior to etching
The initiation and evolution of the localized corrosion in carbon steel were investigated in situ in a simulated marine environment of Xisha Island in the South China Sea
Summary
High strength steels have been used globally for the construction of road installations, electricity posts, utility towers, guide rails, ornamental sculptures and facades and oil and gas pipelines in the marine environment. In the initial stage of pitting process, some corrosion spots are formed in the localized corrosion areas on metal surface due to the dissolution of nanoscale secondary ion sites in the stainless steel, such as MnS [9]. Materials 2018, 11, 2277 cementite and MnS inclusion on corrosion Both MnS and cementite are cathodic phase compared to the matrix, and localized corrosion area can form around them as an anodic area. The interactive effect between cementite and MnS is reported to be closely related to the ratio of carbon to sulfur content (C/S) in the steel [11]. The synergistic effect of Al2 O3 inclusion and pearlite on the localized corrosion evolution process of carbon steel remains unclear. We thoroughly explored the synergistic effect of Al2 O3 inclusion and pearlite on the localized corrosion evolution process of Q460NH steel under a simulative marine environment. Field emission—scanning electron microscopy–energy dispersive spectrometry (FE-SEM-EDS) was employed to characterize the microstructures
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