ナノインデンテーション法を用いたS25Cフェライト相の塑性変形挙動へ与える水素濃度の影響評価

抄録

Hydrogen embrittlement (HE) in steel has been recognized as a problem due to the remarkable reduction of mechanical properties. Regarding the mechanism of hydrogen embrittlement, the influence of solute hydrogen on the behavior of lattice defects has drawn attention, it can not be said that the whole picture has been elucidated yet. Therefore, in this study, the influence of hydrogen concentration on plastic deformation process in polycrystalline S25C ferrite phase was evaluated using nanoindentation method. The depth of indentation was set to 50 nm. Hydrogen charge was carried out using FIP bath. In order to evaluate the effect of hydrogen concentration, we change the exposing time to the atmospheric environment from 0 to 9 days (day 0, 1, 2, 9) after by hydrogen charging. And the specimen without hydrogen charging was also prepared as comparison. The obtained load - indentation depth curve represents the influence by hydrogen, it hardened on the day 0 to the uncharged material, softened on the day 2 and finally the hardness recovered to the original condition on the day 9. Furthermore, hydrogen induced work amount per unit volume after 50 nm indentation was calculated. As a result, a similar tendency was confirmed. These results indicate that the ferrite phase in S25C hardened when the hydrogen concentration is high, softened when the hydrogen concentration is low, and returns to the original condition when the hydrogen concentration is extremely low with the indentation depth of about 50 nm.