Permeation Measurements in the Early Stage of Hydrogen Induced Cracking in Iron and Steels

Abstract

Hydrogen permeation experiments were performed continuously over 45 hours on iron and steels (0.007-0.19%C) by an electrochemical method (nickel-plating method). The hydrogen was charged cathodically with a constant current density, 40A/m², in two buffer solutions. The blisters were observed optically and electron scanning microscopically. The hydrogen diffusivity (D) and hydrogen content (C₀) were kept constant during hydrogen permeation when an acetic buffer solution was used. However, D decreased and C₀ increased with permeation time, when a boric buffer solution was used. In the latter, many blisters were formed in the specimens during the permeation, but there was no blister in the former because C₀ was less than 0.1ppm. Blisters were formed at nonmetallic inclusions, Al₂O₃. These hydrogen permeation behaviors are discussed by the hydrogen trap effect at nonmetallic inclusions and at blisters around nonmetallic inclusions.