Effect of Hydrogen on Fatigue Crack Growth Properties of SCM435 Steel Used for Storage Cylinder in Hydrogen Stations

The effect of hydrogen on fatigue crack growth properties was investigated for two heats of SCM435 steel used for storage cylinder in hydrogen stations. Fatigue crack growth tests were performed for hydrogen-charged and uncharged specimens at stress ratios R = 0.1, 0.4, 0.7 and under the condition fixing the maximum load. An additional tests in 90 MPa hydrogen gas were also carried out at R = 0.1 and 0.5 at 1 Hz. As the results, the threshold stress intensity range ΔKth of the hydrogen-charged specimens obtained at 50 Hz was almost equal to that of the uncharged specimens. This result meant that hydrogen effect was negligible on ΔKth. The results obtained in the 90 MPa hydrogen gas supported this conclusion. In the middle ΔK region, the fatigue crack growth was accelerated by hydrogen. The acceleration, which depended on frequency, was saturated below 0.2 Hz. Maximum acceleration was about 30 times regardless of the stress ratio and the heat of the materials. Also in the hydrogen gas, the fatigue crack growth was accelerated, while the maximum acceleration was coincident with that of the hydrogen-charged specimens. Moreover, the fitted line of Paris low in the hydrogen gas was parallel to that in air in the high ΔK region. Accordingly, the fatigue crack growth in hydrogen gas could be predicted from the test results of the hydrogen-charged specimens.