Microscopic characterization of hydrogen-induced quasi-brittle fatigue fracture in low-strength carbon steel

The microscopic feature of hydrogen-induced quasi-brittle fatigue fracture in low-strength carbon steel was investigated by transmission electron microscopy and electron backscatter diffraction. These analyses, aided also by fractography, explicitly revealed the following points; i) brittle striation is formed by extensive slip at the crack tip, ii) quasi-brittle facet is not crystallographically related to the {100} cleavage plane, and iii) crack growth process is stable. These results may suggest that the crack growth, despite its brittle appearance, is essentially a combined process of extensive slip and significantly localized ductile cracking, which is distinct from the normal slip-off growth mechanism.