Effect of precharging methods on the hydrogen embrittlement of 304 stainless steel

Electrochemical and gaseous hydrogen precharging are representative methods for evaluating hydrogen embrittlement in metallic materials. In this study, the effects of these methods on the tensile properties and microstructural deformation behaviors of austenitic stainless steel (304 L) were investigated. The tensile properties and microstructural deformation behaviors of precharged and unprecharged specimens were compared through conventional and in situ tensile tests, and the resulting differences were verified. Hydrogen precharging causes ductility reduction and changes in the fracture mode of 304 L stainless steel. Microcrack nucleation and propagation were unrelated to the hydrogen precharging method. However, the precharging methods differed in terms of the penetration depth of hydrogen and trapping sites. In the case of electrochemical hydrogen precharging, the hydrogen concentrations on the surface and at the center differed, and hydrogen was mainly trapped in grain boundaries. However, in the case of gaseous hydrogen precharging, the interior had a uniform hydrogen concentration, and hydrogen was mainly trapped inside the lattice. The hydrogen precharging methods induced differences in mechanical properties and microstructures. The effect of hydrogen on the deformation behavior of 304 L stainless steel was the same regardless of the precharging method. However, the effect of hydrogen was observed at different elongated displacement levels depending on trapping sites.