Abstract
The fatigue crack growth behavior in hydrogen gas environment was examined using compact tension specimens of five kinds of materials, i. e., low alloy steels (Ni-Mo-V, Ni-Cr-Mo-V), austenitic alloy steels (18Mn-5Cr, SUH660) and a copper alloy (Be-Cu). The fatigue crack growth rates in laboratory air and hydrogen gas were obtained and the relation between the fatigue crack growth rate and fracture morphology was discussed based on the fractographical observations.
The main results obtained are as follows.
(1) The effect of hydrogen gas on the fatigue crack growth rate was classified into following four types. (a) The effect of hydrogen gas was not observed (18Mn-5Cr, SUH660). (b) A slight decrease in fatigue crack growth rate was observed (Be-Cu). (c) A considerable increase in fatigue crack growth rate was observed, but the effect of frequency was not observed (Ni-Mo-V). (d) A considerable increase in fatigue crack growth rate was observed, and the effect of frequency was also observed (Ni-Cr-Mo-V).
(2) In the materials of types (c) and (d), the cleavage fracture was observed and the area percentage of the intergranular fracture on the fracture surface increased in hydrogen gas. The change of fracture morphology in hydrogen gas had a direct influence on the fatigue crack growth rate.
(3) A good correspondence between the striation spacing and the fatigue crack growth rate was observed in both air and hydrogen gas except for Ni-Cr-Mo-V steel.
