Promotion Effect of Hydrogen on Grain Refinement in Pure Fe by High-Pressure Torsion-Straining

We revealed that hydrogen (H) in pure Fe promotes grain refinement during plastic deformation, which is caused by the increase in dislocation density by the shielding effect and the presence of vacancy-H clusters. The promotion effect of H was dependent on the temperature and the strain rate, which is considered to result from a change in the number density of vacancy-H clusters and the magnitude of shielding effect by H.