The influence of microstructure on the corrosion rate of various carbon steels

This paper presents a fundamental study of the influence of carbon steel microstructure on the corrosion rate. Subsequently, the corrosion performance of various grades of carbon steels were evaluated in stirred autoclaves under elevated carbon dioxide and temperature conditions. Corrosion and penetration rates were determined via mass loss and optical microscopy, respectively. It was found that the corrosion rate of carbon steel line pipe is influenced by microstructure. More specifically, a relationship between localized corrosion susceptibility and the presence of pearlite bands in the steel microstructure was found. However, no correlation was evident between minor elemental concentrations (i.e., Ni, Cr, Mo) and corrosion resistance. It has been proposed that the corrosion stability of the various microstructures may arise from variations in the distribution of carbon bearing phases within the steel. In the banded ferrite/pearlite structure, the carbon-bearing phase (pearlite) is distributed in layers whereas in the other structures the carbon-bearing phases are much more evenly distributed. This study reports on the corrosion resistance of carbon steels in relation to their chemical and physical properties.