Effects of Cu addition on hydrogen absorption and diffusion properties of 1 470 MPa grade thin-walled steel in a solution of HCl

Hydrogen embrittlement is caused by the introduction of hydrogen into steel and is critical for high strength steels. To clarify the effects of the addition of Cu on the suppression of hydrogen embrittlement in a solution of HCl, hydrogen permeation tests and dynamic polarization measurements were conducted on TS 1 470 MPa grade, low-carbon martensite steels. To this end, steels containing 0.19% C, 0.2% Si, 1.3% Mn, Cr, Ti, Nb and B were prepared with and without 0.16% Cu. For comparison, ferrite and pearlite steels were also examined. The results of hydrogen permeation tests indicated that the steady-state hydrogen permeation current (J_H) of steel containing 0.16% Cu was considerably lower than that of basic steel in 0.1 N HCl at the corrosion potential. Moreover, the J_H of martensite steel was suppressed by the addition of Cu, and the cathode current, (i_C) and the J_H/i_C were reduced. The results obtained in this study corroborated the hypothesis that the 1 or 2-μm metallic Cu particles precipitated on the surface of the steel in a solution of HCl suppressed the cathodic reaction and the introduction of hydrogen. The hydrogen diffusion constant (D_eff) was obtained from hydrogen permeation tests under a potential gradient. Cu addition has only small effect on D_eff regardless of microstructure. The occupancy of trap site (n_X) was estimated to be greater than 99% independent of Cu content and microstructure.