This study was conducted to clarify the effects of grain boundaries and precipitates on room-temperature hydrogen transport in two types of austenitic stainless steels with ultrafine-grained structures produced by high-pressure torsion and subsequent annealing. The grains in the Fe–25Ni–15Cr(wt%) alloy containing Ti and the Fe–25Cr–20Ni alloy were refined by the high-pressure torsion-processing to ∼150 and ∼85nm, respectively. The high-temperature annealing after the high-pressure torsion processing led to the precipitation of η-Ni3Ti for the former and σ-FeCr for the latter. In the high-pressure torsion-processed specimens, hydrogen diffusivity was enhanced through short-circuit diffusion because of the increased population of grain boundaries in comparison with the increased opportunity of hydrogen trapping on dislocations. As for the post high-pressure torsion-annealed specimens having the precipitates, the hydrogen diffusion was hindered by the hydrogen trapping on η-Ni3Ti precipitates, but was not affected by σ-FeCr precipitation. This depends on the affinity between hydrogen and constituting elements.

Grain-Boundary Diffusion and Precipitate Trapping of Hydrogen in Ultrafine-Grained Austenitic Stainless Steels Processed by High-Pressure Torsion. Y.Mine, K.Tachibana, Z.Horita: Materials Science and Engineering A, 2011, 528[28], 8100-5