Effect of δ-ferrite on Susceptibility to Hydrogen Embrittlement of 304 Austenitic Stainless Steel in High-Pressure Hydrogen

304 austenitic stainless steel was treated by solid solution at 1 050℃ to change the content of δ-ferrite structure, and then the slow strain rate tensile test and fatigue crack growth test were carried out in high-pressure hydrogen and argon, respectively. The effect of δ-ferrite on the susceptibility to hydrogen embrittlement of the tested steel was investigated. The results show that a ralatively large amount of δ-ferrite existed in original structure of the tested steel. After solid solution at 1 050℃, the δ-ferrite almost disappeared. In high-pressure hydrogen, the existence of δ-ferrite reduced the plasticity of the tested steel and enhanced the susceptibility to hydrogen embrittlement. The presence of δ-ferrite provided a fast diffusion channel for hydrogen and improved the fatigue crack growth rate of the tested steel.