Direct observation of the influence of grain orientation on the corrosion of pipeline steels

This study aims to correlate the crystallographic texture of pipeline steels with their corrosion resistance. Electron backscatter diffraction (EBSD) was used to investigate the impact of grain orientation on the corrosion behavior of steels in various corrosive environments. Corrosion is influenced by several microstructural features, such as phase composition, grain size, grain boundary character, dislocation density, and crystallographic texture. To analyze the influence of specific grain orientations on corrosion resistance, steel samples were subjected to planned thermomechanical treatments to obtain samples with similar microstructures but different crystallographic textures. These samples were then exposed to controlled corrosive environments, and their microstructural changes were mapped using EBSD, scanning electron microscopy, and 3D optical profilometry. The results obtained indicated that corrosion response depends on grain orientations. Notably, the steel with more 〈111〉//ND and 〈100〉//ND grains exhibited improved corrosion resistance compared to the steel with a more random texture. The resistance of grains to active dissolution in all the corrosive solutions was in this order: {110} < {111} < {100}. The corrosion products were analysed using XPS, revealing variations in the composition and nature of the surface films on the samples across the selected electrolytes.