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To examine a possible contribution of hydrogen on the crack initiation andpropagation behaviour of high strength bolt steel, ASTM A490, fatigue tests was carried outunder hydrogen environment. The conventional fatigue limit in air that is 300 MPa,disappears in hydrogen environment and shows unexpectedly low stress level around50MPa at 107 due to the subsurface development of mechanistic damage caused byhydrogen. Test results show that fatigue-dominated mode of fracture at higher stress levelsand the hydrogen-dominated mode of fracture at lower stress levels describe the nature ofthe fatigue fracture in hydrogen environment. Appearance of the QC facet on the fracturesurface due to hydrogen should explain the initiation and propagation of the crack at thestress level far below the fatigue limit in air.