Hydrogen Entry into Steel Under Corrosion Products

Hydrogen entry into high-strength steel after local sodium chloride predeposition and during exposure to humid air was studied using scanning Kelvin probe. Two regions with different pH, potential, and red rust composition were formed on the corroding side of the specimen. Hydrogen permeating through the specimen was detected over the region with the net cathodic character, which was linked to oxygen reduction taking place on top and within the red rust layer whereas anodic dissolution progressed inside the rust covered pits creating conditions favorable for formation of hydrogen ions. No measurable hydrogen entry was detected in the area covered with an apparently homogeneous layer of corrosion products and corroding uniformly. The finding that corrosion pits were the main source of atomic hydrogen implies that the susceptibility of high-strength steels to pitting corrosion is an important parameter for evaluation of the risk of hydrogen embrittlement under atmospheric conditions.