純鉄における水素助長疲労き裂進展のマルチスケール解析

抄録

For the storage and transportation of compressed gaseous hydrogen in forthcoming hydrogen energy-based society, hydrogen-assisted fatigue crack growth (HAFCG) in structural steels is one of the most considerable problems from the perspective of life-cycle assessment or safety use of the hydrogen-containing components. In this study, fatigue crack growth tests of a commercially pure iron were conducted in laboratory air and 0.7 MPa gaseous hydrogen at room temperature, in order to elucidate the fundamental mechanism dominating the crack growth acceleration in steels with BCC lattice structure. The tests revealed dramatically accelerated crack growth rate in presence of hydrogen in association with significant change of fracture morphology (ductile striations to quasi-cleavage). The mid-thickness fracture paths in air and hydrogen were analyzed by using several characterization techniques including electron-backscattered diffraction (EBSD), electron channeling contrast imaging (ECCI), and transmission electron microscopy (TEM), achieving critical and direct evidence indicating that hydrogen dramatically suppressed the evolution of dislocation structure beneath the fracture surface and enhanced the fracture along {100} plane . These results implicate that the cause of HAFCG in BCC steels is the hydrogen-induced reduction of the interatomic cohesive force, leading to the fracture along cleavage plane, in addition to the localization of plasticity into the crack tip region as was reported in previous research.