Hydrogen embrittlement of In-RAFM steel investigated with in-situ tension testing through electrochemical charging

RAFM steels have been developed to serve as the structural components of test blanket module (TBM) of ITER fusion reactor. One of the main issues in the application of candidate materials for TBM structural is their exposure to hydrogen from transmutation reaction (n-p) and external sources such as water and helium gas used for cooling. Hydrogen embrittlement (HE) is a complex phenomenon involving a number of parameters such as microstructure, temperature, loading mechanism and hydrogen interaction means. These variables influence differently to the phenomenon in a diverse fashion. For inferring meaningful insights about hydrogen embrittlement (HE), one of the prevalent means is to undertake mechanical testing with in-situ cathodic charging. The current work is to study manifestation of HE in an Indian RAFM (In-RAFM) steel, developed for fabrication of test blanket module (TBM) for ITER. For this purpose, in-situ tensile experiments under hydrogen introduction by cathodic charging have been carried out over a range of current density (∼20 to 3.8 x 10³ mA/cm² ). In contrast with un-hydrogenated material, cathodic charging results in substantial reduction in both strength and ductility. However, further rise in current density (∼80 to 3.8 x 10³ mA/cm² ) resulted in additional lowering in ductility with slight hardening. To explain the trends, fractographic studies have been carried out. Exposition of the observed HE findings has been critically discussed in light of current acquaintance. (author)