Microelectrochemical heterogeneity of ferric-pearlitic structures

Using a method developed for other investigations [1], we studied the distribution of electrode potentials on the surface of a microsection of St. 20 steel annealed in vacuum for 10 hr at 1200°C. To increase the resolving power of the microelectrochemical method used, we increased the H₂O₂ concentration in the electrolyte [1]. This not only increased the concentration of iron ions in the immediate vicinity of the electrodes but also enriched the solution with hydroxyl ions which promoted extensive hydrolysis of FeCl₃ leading to the formation of Fe(OH)₃ which passed into a colloidal state and gave no reaction for iron ions. As a result, a passivating film was formed on the specimen surface so that it was impossible to carry out potential measurements. We therefore changed the composition of the electrolyte: sulfuric acid was introduced instead of hydrochloric acid.