Fatigue Crack Growth Characteristics of JIS SUS316L Austenitic Stainless Steel in a Hydrogen Gas Environment

In order to clarify the effects of a hydrogen gas environment on the fatigue characteristics of stable austenitic stainless steels, bending fatigue tests were carried out on SUS316L in a H2 gas, in a N2 gas of 1.0 MPa and in air. The fatigue tests were also carried out on a metastable austenitic steel SUS304 as a material for the comparison. The main results obtained are as follows. Hydrogen gas accelerates the fatigue crack growth rates of both materials. The fracture surfaces of the both materials consist of two parts practically ; the faceted area seemed to be brittle and the remaining area seemed to be ductile. The faceted area does not significantly contribute to the acceleration of the fatigue crack growth rate, but the ductile fracture mode predominantly does. The slip-off mechanism seems to be valid not only in air and in N2, but also in H2. The fatigue crack growth acceleration by hydrogen occurs in this mechanism. The difference of the degree of the acceleration, which is smaller in SUS316L than in SUS304, seems to be caused by the difference in the stability of γ phase.