Abstract
Hydrogen entry into high strength steel has been investigated by hydrogen permeation measurements under wet-dry cyclic environments. Dominant environmental factors that control hydrogen entry were temperature, relative humidity, and the amount of sea salt on the steel surface. Corrosion rate increased with an increase in temperature, resulting in enhanced hydrogen permeation. Hydrogen entry was promoted at lower relative humidity (40–60%), by the hydrolysis of Fe3+ accelerated by condensed Cl− ions in the water layer. A maximum hydrogen permeation coefficient was observed at the Cl− amount of 0.03 kg/m2 on the steel surface, corresponding to a maximum corrosion rate determined by an appropriate water layer thickness. Crack susceptibility of the steel has also been investigated by stress fracture tests under wet-dry cyclic environments. Steels with tensile strengths beyond 1400 MPa suffered from cracking at higher temperatures and the Cl− of 0.03 kg/m2. The fracture test results mean that crack susceptibility strongly depended upon the environmental severities which promoted hydrogen entry.
