Effects of hydrogen environment on fatigue characteristics in a type 304 austenitic stainless steel

In order to clarify the effects of hydrogen on the fatigue characteristics of an austenitic stainless steel, bending fatigue tests on plain specimens were conducted in air and in a hydrogen gas. Main results obtained are as follows. Effects of hydrogen are not clearly seen on the fatigue strain-life diagram, because the hydrogen gas environment has opposite effects to crack propagation and to crack initiation ; accelerates crack propagation, but retards crack initiation. Striation spacing or in-situobservations confirm the acceleration. The cause of retardation seems to be the lack of oxygen or water vapor in the hydrogen. Several cracks propagate in air, but only one crack occurred in hydrogen. The difference in the number of cracks is supposed to depend on the ratio of the crack initiation life to fatigue life.