The overall (anodic + cathodic) electrochemical reaction describing carbon dioxide corrosion of iron, carbon, and low alloy steels is:

$$Fe + C{O_2} + {H_2}O \to FeC{O_3} + {H_2} \label{eq:1}$$

A formal definition of carbon dioxide corrosion can be found in this post.

LaTex Code

Fe + C{O_2} + {H_2}O \to FeC{O_3} + {H_2}