Abstract
The mechanism of the degradation of corrosion for deformed Type 304 steel exposed to 28 MPa hydrogen at 673 K for 57.6 ks has been investigated by electrochemical measurements. The anodic polarization curve of hydrogen-charged martensitic Type 304 steel in H2SO4 solution shows three anodic peaks at the potentials of −0.4, −0.3 and −0.05 V vs. SCE, whereas that of hydrogen-charged austenitic steel does the peaks at −0.3 and −0.05 V vs. SCE, but not the peak at −0.4 V vs. SCE. Severe corrosion was observed on the hydrogen-charged martensitic steel when it was held at −0.4 V vs. SCE in H2SO4 solution. This severe corrosion was prevented by heating the steel at 923 K, although it was not avoided up to 873 K. It was found that the cathodically hydrogen-charging at ambient temperature induced martensite phases in the austenitic steel, and it did a hydride phase at 373 K. The anodic polarization curve of Type 304 steel containing a hydride phase revealed an anodic peak at −0.5 V vs. SCE, while that of the steel containing hydrogen-induced martensite phase did not produce the peak at −0.4 V vs. SCE. Consequently, the degradation of corrosion of deformed and hydrogen absorbed Type 304 steel can be ascribed to the selective corrosion of hydride in martensite phases by deformation.
