Hydrogen embrittlement phenomenon in pure iron was investigated by cyclic creep with aid of hydrogen charging.
Pure iron was machined into specimens with gauge length of 25 x 4 x 1 mm, which were annealed for 2hrs at 1223K and furnace cooled after, which yield stress was 140 MPa and grain size was 0.06-0.08 mm.
In this study, creep strain is increased by hydrogen charging, that is originated from increased dislocation density and some microcracks or microvoid in the specimen by hydrogen charging.
Cyclic creep acceleration is observed and degree of cyclic creep acceleration is independent of stress.
Below the critical stress for crack propagation, cyclic creep acceleration seems to be occured because of recovery by means of climb of edge dislocation and cross slip of screw dislocation upon unloading, and because of enhanced dislocation mobility by oscillation of dislocation under cyclic stress.
Above the critical stress for crack propagation, it is believed that cyclic creep acceleration was occured by both the same mechanism of cyclic creep acceleration as stated above and microcrack propagation in the specimen.
Increased dislocation density and crack propagation in cyclic creep with aid of hydrogen charging were caused by hydrogen pressure build up in defects such as microcracks and microvoid.
From the above, it is believed that planer pressure theory is more valid than any other theories for this study.
