Specific Features of Corrosion and the Microelectrochemical Heterogeneity of 45 and U8 Steels in Hydrogen-Sulfide Media

Abstract

We analyze the character of corrosion of 45 and U8 steels with ferrite–pearlite (pearlite), sorbite, troostite, and martensite structures in hydrogen-sulfide media. It is shown that, as a result of hydrogen-sulfide corrosion, sulfide-containing films are formed on their surface. It is established that the degree of localization of pits and the depth corrosion indices depend on the structures of steels and their grades. Corrosion pits develop most intensely on the surfaces of steels with martensite (U8 steel) and troostite (45 steel) structures. We analyze the microelectrochemical heterogeneity of the surfaces of these steels prior to and after hydrogen-sulfide corrosion by the method of scanning with a capillary probe in a moving drop of an МЕХ aqueous solution. It is shown that, for 45 steel with troostite structure, it increases by a factor of ∼ 7. The local potentials take their highest values at the sites of the largest corrosion pits and attain 300 mV.