Effect of Hydrogen Charging Conditions on Hydrogen Blisters and Pitting Susceptibility of 445J1M Ferritic Stainless Steel

The surface morphology and pitting susceptibility of 445J1M ferritic stainless steel in a NaCl solution before and after hydrogen charging were investigated using the atomic force microscope, X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization, critical pitting temperature and the electrochemical impedance spectroscopy measurements. The content of hydrogen in 445J1M stainless steel increased from 1.7 ppm to 4.8 ppm with increasing the hydrogen-charging current density from 0 mA/cm2 (uncharged) to 25 mA/cm2. Hydrogen charging has induced blisters on the sample surface but not caused significant changes in the surface roughness. The size of hydrogen blisters on the samples increased with the rise of hydrogen charging current density. No direct connection could be found between the locations of hydrogen blisters and pitting nucleation. The pitting susceptibility and the instability of passive films both increased with the hydrogen-charging current density as shown by the electrochemical and XPS results. The breakdown potential decreased significantly with the increase of hydrogen-charging current density, accompanied by an increased passive current density. The decreased content of metal oxides in the passive films and the additional hydrogen oxidation reactions related to the permeated hydrogen can account for the deteriorated corrosion performance of the 445J1M ferritic stainless steel after hydrogen charging.