Effect of hydrogen concentration on fatigue crack growth behaviour in pipeline steel

The ambiguous relationship between fatigue crack growth rate and hydrogen concentration CH in the bulk of metal under cyclic loading of the ferrite-pearlite low-alloyed steel in hydrogen-contained environments has been found: there is a certain CH value at which the crack growth resistance of steel increases. At these test conditions fracture surface demonstrates some increasing of the plastic component on relief. The received results point on key importance of the determining of such threshold hydrogen concentration values, which correspond the transition “enhanced plasticity - embrittlement”.