Corrosion-induced hydrogen evolution, absorption, and cracking behaviors of ultra-high-strength galvanized and galvannealed steel sheets

Abstract

Various experimental analyses on hydrogen evolution, absorption, and cracking behaviors were conducted to gain a fundamental understanding of the hydrogen embrittlement of ultrastrong steel sheets with galvanized (GI) and galvannealed (GA) coatings. The hydrogen evolution and absorption behaviors are controlled primarily by the potential differences between the coating and exposed steel substrate, and the corrosion-induced damage pattern of the coating. The higher absorption rate of hydrogen was more pronounced in corroded GI-coated steel caused by the larger cathodic polarization applied to the exposed substrate, and a more severe form of coating dissolution by aqueous corrosion in a 3.5% NaCl + 0.3% NH4SN solution. In contrast, the corrosive species can only penetrate through the pre-existing cracks in the brittle Fe-Zn intermetallic phases composed of the GA coating, and the driving force for hydrogen evolution becomes smaller. These result in significant differences in hydrogen penetration and cracking behaviors between the two coated ultrastrong steels.