Low Pressure Hydrogen Gas Effect on Extremely Low Fatigue Crack Growth from Small Blind Holes of SUS304 and SUS316L

In order to investigate the hydrogen gas effect on the fatigue limits of austenitic stainless steels, SUS304 and SUS316L, with small twin blind holes, metal fatigue tests were carried out in low pressure hydrogen gas, in air and in inert gases; i.e., argon or nitrogen. The fatigue limit of SUS304 is defined as the crack propagation limit not only in air, but also in hydrogen and nitrogen. The fatigue limit of SUS304 in hydrogen gas is slightly higher than that in air. The extremely low Fatigue Crack Growth Rates (FCGR) of not only SUS304, but also SUS316L in hydrogen gas is lower than that in argon gas in the FCGR region of less than 10-9m/cycle. This seems to be due to the plasticity-induced crack closure, and supports the higher fatigue limit in hydrogen.