Anomalous Corrosion of Hydrogen-Containing Ferritic Steels in Aqueous Acid Solution

The effect of dissolved hydrogen in soft iron and ferritic low alloy steel on general corrosion was investigated in acid solutions. Hydrogen charging was carried out in 1 to 28 MPa hydrogen at 723 K for 57.6 ks. Weight loss of hydrogen charged ferritic steels was markedly greater than that of hydrogen-free ones, and increased with increasing hydrogen content. Plastic deformation of steels increased the dissolved hydrogen content, and the anomalous corrosion increased with cold working ratio. Anodic polarization curves of hydrogen charged soft iron and low alloy steel in 0.5 kmol/m3-H2SO4 solution exhibited an increase of current density in the passive region in agreement with the corrosion data. This anomalous corrosion was partly recovered by dehydrogenation heating at 573 to 1223 K. The anomalous corrosion was dependent on the residual hydrogen content and independent of the structure. It is suggested that the anomalous behavior is caused by activated internal microdefects in steel formed by hydrogen trapping.