Correlation between hyperfine structure of inclusion and localized corrosion mechanism of DSS2101 with Ce microalloying in simulated marine environment

Abstract

The discrepancies in inclusion characteristics and localized corrosion behaviour and mechanism induced by inclusions in DSS2101 are contrastively investigated. We found that the two types of inclusions consisted of (Al, Mn, Cr)–O–S and (Ce, Al, Mn)–O–S. Numerous twins and denser entangled dislocations were distributed near the (Al, Mn, Cr)–O–S/matrix. The distorted and normal BCC phase exhibited the {1‾10}N∥{1‾12}D orientation relationship, whereas severe lattice expansion existed along the {01‾2} and {1‾20} crystallographic directions, presumably resulting in the priority initiation of pitting. Besides, the (Al, Mn, Cr)–O, (Al, Mn)–O core and CeAlO3 shell had especially poor electrical conductivity, making formation of the galvanic couple difficult. However, the deformed matrix served as an anode relative to the normal matrix (as a cathode), facilitating pitting rate of Ce-free steel. In contrast, the electrochemical reaction of MnS (as an anode) and the chemical reaction of the CeAlO3 shell protected the adjacent matrix (as a cathode) from erosion by self-dissolution in Ce-modified steel. The synergistic effect of the differential aeration cell (DAC) and occluded corrosion cavity (OCC) was supposed to deteriorate the microcrevice corrosion and galvanic corrosion.