Ductility loss of hydrogen-charged and releasing 304L steel

The mechanical properties and fracture behavior of 304L austenitic stainless steel after cathodic hydrogen charging and hydrogen spontaneously releasing are investigated by tensile tests. Flat tensile specimens were cathodic hydrogen charged at various current densities. For each density, two specimens were charged at the same condition. When the charging process completed, one specimen was tensile immediately to fracture and the other was aged to release the hydrogen out of it and then was also tensile to fracture. The resulting tensile properties and micrographs of fracture surfaces of these specimens were evaluated and compared. The results show ductility loss occurred in the hydrogen-charged specimens and the loss increased as the current density increasing. After hydrogen releasing, the specimens recovered a certain extent but not all of its original ductility. Scanning electron microscope (SEM) micrographs of fracture surfaces reveal that irreversible damage had developed in the hydrogen-releasing specimens during the releasing process rather than the charging process. This consequence can be ascribed to the high tensile stress caused by non-uniform hydrogen distribution during hydrogen releasing.