The present study investigated the hydrogen-related fracture behavior under stress concentration in a low-carbon martensitic steel. Double-notched sheet-type specimens with different diffusible hydrogen contents were prepared, and tensile tests were performed until just before the fracture for observing the crack initiation and propagation. When the specimen contained the smaller amount of diffusible hydrogen, a large crack formed at the position where the equivalent plastic strain was the largest. The crack propagated mainly along {011} planes within prior austenite grains. By contrast, in the case that the specimen contained the larger amount of diffusible hydrogen, the hydrostatic tensile stress controlled the...