Effect of Hydrogen and Frequency on Fatigue Behavior of SCM435 Steel for Storage Cylinder of Hydrogen Station

Abstract

Fatigue tests on SCM435 steel quenched at 860°C and tempered at 580°C were carried out under the frequencies of 0.2, 2 and 20 Hz with specimens containing a small artificial hole. An additional test in which the frequency was alternatively switched between 0.02 Hz and 2 Hz was also carried out. Hydrogen charging to specimens was carried out by immersion method. The fatigue life of hydrogen-charged specimens decreased in comparison with that of uncharged specimens. The acceleration of fatigue crack growth rate da/dN was observed at dα/dN<1.0×10-7m/cycle in test frequency f=20 Hz, dα/dN<4.0×10-7 m/cycle in f=2Hz and dα/dN<1.5×10-6 m/cycle in f=0.2 Hz. The acceleration of dα/dN saturated at ΔK<17 MPa√m in f≤2Hz. It was found that there is the upper bound of the effects of hydrogen and test frequency on fatigue crack growth rate in hydrogen environment. The test with switching two frequencies between 0.02 Hz and 2 Hz showed that hydrogen concentration in the vicinity of the crack tip remarkably affects fatigue crack growth behavior and crack morphology. The most remarkable change of the slip bands around the crack tip was less and discrete in the hydrogen-charged specimens compared to uncharged specimens.