Hydrogen Assisted Fatigue Crack Growth in a Precipitation-Hardened Martensitic Stainless Steel Under Gaseous Hydrogen

In this study, the effect of gaseous hydrogen on the fatigue crack growth behavior in a precipitation-hardened martensitic stainless steel is investigated. It is known that the degradation in fatigue crack growth behavior derives from a complex interaction between the fatigue damage and the amount of hydrogen enriching the crack tip, which is dependent on the hydrogen pressure, loading frequency, and stress intensity factor amplitude. Therefore, fatigue crack growth tests were performed in a range of 0.09 to 40 MPa under gaseous hydrogen at a frequency of 20 and 0.2 Hz. The fatigue data as well as fracture morphologies obtained so far indicate a sharp increase in crack growth rates in a narrow range of stress intensity factor amplitudes. Also, it is shown that by decreasing the loading frequency to 0.2 Hz at a given pressure of hydrogen the transition occurs at lower values of stress intensity factor amplitudes accompanied by a change in fracture mode. Scanning electron microscope (SEM) observations of the fracture surfaces are used to support the explanations proposed to account for the observed phenomena.