Hydrogen-Induced Phase Transformations in Type 304L Stainless Steels

Electrolytic charging of hydrogen onto Type 304L stainless steel at room temperature and 100 C (212 F) induced partial transformation of the austenite to the same martensitic phases [α′(bcc) and ε (hcp)] as are formed by cold-working hydrogen-free austenite at low temperatures (-196 C) (-321 F). No evidence of a hexagonal hydride was found. The formation of the ε phase by cathodic charging suggests that hydrogen lowers the stacking fault energy of austenite. Hydrogen charging expands the austenite lattice, causes the dislocation and stacking fault density to increase with increasing hydrogen concentration, and causes dislocation movement.