Fretting fatigue properties of SCM435H and SUH660 in hydrogen gas environment

The objective of this study is to clarify the effect of hydrogen gas environment on fretting fatigue strength of the materials for hydrogen utilization machines and structures. The materials used in this experiment were a low alloy.steel SCM435H and a precipitation hardened stainless steel SUH660. And the effectiveness of nitriding, which has been used to improve fretting fatigue strength, was examined in hydrogen gas environment. Hydrogen gas pressure was 0.12 MPa in absolute pressure. Continuous measurement of fretting fatigue crack propagation during the test in hydrogen gas was done by using an electric potential drop technique in order to consider the mechanism of hydrogen function. Fretting fatigue lives of both materials in the short-life region were increased in hydrogen gas than in air. This was caused by that start of stable crack propagation was delayed in hydrogen gas environment. However, in SUH660, fretting fatigue strength in hydrogen gas was decreased than that in air in the long-life region, which is more than 10⁷ cycles. In the fretting fatigue test of SUH660 in hydrogen gas at 18% lower stress amplitude compared with the fretting fatigue strength in air at N=3 × 10⁷ cycles, a failure occurred at N=3 × 10⁷ In SCM435H, fretting fatigue strength was the same in both environments even in long-life region.