Corrosion Assessment and Characterization of Aerospace-Bearing Steels in Seawater and Ester-Based Lubricants

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The corrosion behavior of bearing steels was screened using potentiodynamic scans in seawater. The results of electrochemical testing provided a relative ranking of the bearing steels when tested in aqueous chloride-containing solution. The corrosion behavior of bearing steels in the lubricant environment has been observed to be quite different than in aqueous solution. Both the amount of water contamination in oil and chloride content of the water impact the observed corrosion rates in oil-water mixtures. All steel compositions tested demonstrated localized corrosion damage when exposed to oil with water added; however, inherently less corrosion-resistant alloys had more widespread shallow attack, whereas higher Cr-containing alloys displayed more localized severe attack. The mechanism of corrosion in the two-phase, oil plus aqueous phase system appears to be controlled by an aqueous corrosion process dependent on steel microstructure and emulsified or free water and likely limited by oxygen availability and amount of water (with aggressive ions) in the oil.