Hot Dip Galvanized Steel In The Marine Atmosphere Of Hydrogen Permeation Behavior And Embrittlement Research

As an effective protection measure, zinc coating prevents corrosion of steel through a barrier effect and a galvanic effect. On the other hand, it also acts as a barrier for hydrogen entry into steel substrate because the reduction of water on zinc coating is more hardly than that on iron and the diffusivity of hydrogen in zinc is also smaller compared with iron. However, if zinc coating was damaged and exposed to corrosive environment, such as marine atmosphere, the exposed steel substrate would act as cathodic sites where hydrogen was generated by the reduction of water molecule. For engineering purpose, therefore, it is necessary to estimate the amount of hydrogen absorbed by galvanized steel into the substrate steel when exposed to marine atmospheric environment. In this article, a new technology, which was called hybrid wire beam electrode (WBE), was used to prove that hydrogen must generate on the steel surface if zinc coating damaged. Hydrogen permeation current curve of hot-dip galvanized steels in marine atmosphere was also measured using a modified Devanathan-Stachurski cell. Influences of temperature, humidity, coating defect and amount of sulphite on samples'surface were also investigated. The stress-strain curves of galvanized steel with different hydrogen charging conditions were obtained by SSRT, and their mechanical properties was compared. Fractography were also carried out to investigate the effect of hydrogen permeation zinc coating with defect in seawater on the mechanical properties of steel substrate. The results as follows:(1) The hybrid-WBE was developed and measured the hydrogen generation current density. The results showed that the hydrogen generation current became larger firstly and then reduced as follows as the surface of steel increasing. The wet-dry marine atmosphere can accelerate the hydrogen generation.(2)The atmospheric environment at elevated temperature and humidity accelerates the hydrogen permeation process; meanwhile, cathodic protection of zinc coating to the exposed steel surface promotes the hydrogen absorption of the defective coated steels; the deposition of sulphite can also accelerates the hydrogen permeation process.(3) Self hydrogen permeation behavior of Galvanized coating in marine atmosphere can reduce their percentage elongation after fracture. With longer hydrogen charging time, the materials showed higher susceptibility to hydrogen embrittlement.