The Role of Cementite in the Acidic Corrosion of Steel

Iron carbide (cementite) was isolated from specially prepared carbon‐iron alloys by a selective (chemical) dissolution of ferrite in alcoholic . Cathodic polarization studies on cementite electrodes have shown that this compound is an active cathodic site in corrosion of steel in that it does not polarize at low current densities. At high current densities, however, cementite rapidly polarizes to the potential which is characteristic of iron under similar current density conditions. This is considered the result of the chemical decomposition of cementite to iron and a variety of hydrocarbons under the influence of the cathodically evolved hydrogen. A number of hydrocarbons (predominantly methane) and carbon monoxide mixed with the evolved hydrogen have been identified by mass spectrometry.