Influence of Hydrogen on Local Mechanical Properties of Pure Fe with Different Dislocation Densities Investigated by Electrochemical Nanoindentation

In order to investigate influence of dislocation density on hydrogen embrittlement behavior, local mechanical properties of pure Fe with different dislocation densities were measured during hydrogen charging at various load duration times by electrochemical nanoindentation. For as-annealed samples and severely plastically deformed ones with low temperature annealing, hydrogen charging did not change 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 at longer load duration times. Consequently, it was found that hydrogen causes softening for samples with higher dislocation density at slower strain rates. The observed softening seems to be caused by increase in dislocation mobility or suppression of work-hardening due to hydrogen atoms trapped around dislocations.