The trapping behavior of S-associated defects in steel was studied by using electrochemical permeation techniques. The apparent diffusion coefficient of H, after taking account of reversible and irreversible trapping by S-associated defects, could be described by:

D (cm2/s) = (1.12 x 10-6) [1 + 0.0933S(ppm[wt])0.548]-1

The parameters which were associated with reversible and irreversible trapping increased with increasing S content; thus suggesting that there was an increase in both reversible and irreversible trap sites with increasing S concentration.

Trapping of Hydrogen by Sulfur-Associated Defects in Steel. M.Iino: Metallurgical Transactions A, 1985, 16[3], 401-9