Correlation of Corrosion Information Aquired by Indoor Acceleration Testing and by Real Low Temperature Marine Atmosphere Exposure in Polar Region for Ni-Cr-Mo-V Steel
In order to investigate the applicability of the proposed indoor accelerated test spectrum,which aims to simulate the low temperature marine environment in the polar region,and the corrosion mechanism of low alloy steel exposed in the real polar low temperature atmospheric environment,there-fore,the Ni-Cr-Mo-V steels were subjected to indoor accelerated test in lab and to outdoor exposure test in Zhongshan station at the polar region respectively,then the corrosion behavior of the tested steels was comparatively studied by means of mass loss measurement,scanning electron microscope,and laser confocal microscope.The results revealed that the corrosion rate of the steel is 11.3 μm/a,and the corro-sion products are composed of Fe3O4,γ-FeOOH,α-FeOOH and β-FeOOH.The presence of the large amount of β-FeOOH indicates that the rust scale formed in low temperature environment has poor protec-tiveness.The low temperature atmospheric corrosion is mainly uniform corrosion.The freeze-thaw cycle causes the alteration of electrolyte concentration on the surface of test steel,which results in the forma-tion of pitting corrosion beneath the rust scale.During the freeze-thaw cycle,the alternation of stresses caused by the cyclical solid-liquid phase transition of the water in the rust scale and the difference of the thermal expansion coefficient between the rust scale and the metal matrix could lead to the cracking of the rust scale.
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