Evaluation of stress and hydrogen concentration at grain boundary of steels using three-dimensional polycrystalline model

Ebihara, Kenichi   ; Itakura, Mitsuhiro  ; Yamaguchi, Masatake   ; Kaburaki, Hideo; Suzudo, Tomoaki   

The decohesion model in which hydrogen segregating at grain boundaries reduces cohesive energy is considered to explain hydrogen embrittlement. In order to verify the decohesion model, it is necessary to evaluate stress and hydrogen concentration at grain boundaries under experimental conditions. Thus, we calculated the stress and the hydrogen concentration at grain boundaries in the 3-dimensional polycrystalline model generated by the random Voronoi tessellation. The crystallographic anisotropy was given to each grain as a characteristic. As the boundary conditions, data extracted from the results calculated in the notched round-bar specimen model under the tensile test condition was given to the polycrystalline model. As a result, it was found that the evaluated stress does not reach the fracture stress estimated by first-principles calculations. Therefore, it was considered that the initiation of grain boundary fracture needs some factors except the crystallographic anisotropy.