A cyclic wet/dry accelerated corrosion test was used to compare the corrosion behavior of medium-Mn steel and Q345 steel. In terms of scanning electron microscope (SEM), using X-ray diffraction (XRD), electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS), and analysis of the corrosion process, the results showed that the medium-Mn steel did not exhibit higher corrosion resistance than Q345 steel due to the greater content of Mn-rich compounds in the rust layer. Moreover, the effect of a small amount of anti-corrosion elements in medium-manganese steel can regulate the corrosion rate. The conceptual model of the corrosion process of the medium-Mn steel in a 3.5 wt % NaCl solution is proposed.

Carbon dioxide corrosion behavior of low-alloy pipeline steel with 1% Cr exposed to CO₂-saturated solution was investigated by immersion experiment. SEM, EDX, TEM, EPMA and XRD were utilized to investigate the microstructure, corrosion morphologies, corrosion phases and elements distribution of corrosion scale. The results demonstrate that the microstructure of tested steel consists of ferrite and carbides. During the corrosion process, ferrite dissolves preferentially, leaving carbide particles behind. The residual carbide particles may promote the nucleation of FeCO₃ crystal. The phase comprising of the inner layer is Cr compound, and the one of the outer layer is FeCO₃. The formation process of corrosion scale can be illustrated as follows: Firstly, a thin scale consisting of thin inner layer and outer layer is formed, which represents poor corrosion resistance; then, the inner layer changes little, once it has been formed, and the outer layer becomes thick and compact, which demonstrates that a fine corrosion resistance is obtained. The chemical elements of chromium and molybdenum accumulate in the inner layer of corrosion scale. The corrosion behavior of low-alloy steel based on microstructure and morphology characterization is also discussed.