Effect of Microstructural Defects on Hydrogen Absorption for Steels in Acidic Sulfate Solution

Abstract

Effect of hardness of steels on hydrogen absorption behavior has been investigated by means of conventional electrochemical hydrogen permeation test. Empirical transient curves of hydrogen permeation current density were agreed with the theoretical one on the basis of Fick’s second law with a fixed hydrogen concentration at the hydrogen absorption surface, C₀, at any time. The fact suggests quasi-equilibrium condition to the absorption-desorption reaction of hydrogen at the surface, and that correlation between C₀ and hydrogen absorption rate. As an analytical result of the transient, a diffusion coefficient of hydrogen, D, decreased with an increase in a hardness of the steel. On the other hand, the value of C₀ increased with an increase in the hardness. There was a good positive correlation between C₀ and an inverse of D in spite of difference in the hardness and the additional element. The fact may suggest that the microstructural defects attract hydrogen both in the bulk and on the surface of the steel, and the effect promotes hydrogen ad-atom absorbing into the iron specimen.