The CaCO3 influence on the corrosion properties of low carbon steel in aqueous solutions saturated with CO2 and NaCl at 80 degrees C and 15 MPa was investigated over time with respect to morphology, thickness, structure, chemical composition and corrosion rate. The corrosion product formed in CaCO3-based solution was a calcium-enriched siderite and the scales were thinner and more porous than the ones formed in solutions without CaCO3. The CaCO3 reduced the corrosion rate, but the scales produced in the presence of this compound presented depassivation followed by formation of pits during electrochemical measurements effectuated on corroded samples. (C) 2015 Elsevier B.V. All rights reserved.