Influence of Hydrogen on Nanohardness of Pure Iron with Different Dislocation Densities Investigated by Electrochemical Nanoindentation

To investigate influence of dislocation density on hydrogen embrittlement behavior, nanohardness of pure Fe with different dislocation densities was measured during hydrogen charging by electrochemical nanoindentation. For as-annealed samples and severely plastically deformed ones with annealing, hydrogen charging did not affect nanohardness at any load duration times between 1 s and 10800 s. On the other hand, for cold-rolled samples and severely plastically deformed ones without annealing, hydrogen charging caused softening, and the degree of the softening increased with increase in load duration time. Consequently, the tendency was found that hydrogen caused softening for samples with higher dislocation density at slower strain rates. The softening seems to be caused by increase in dislocation mobility or suppression of work-hardening due to hydrogen around dislocations.