TEM study the corrosion behavior of the low alloy steels developed for flue gas desulfurization system

This study investigated the corrosion behavior and underline mechanisms of low alloy steels with a minor addition of 0.4 wt% Cu, 0.2 wt% Ni, 0.1 wt% Sb and 0.05 wt% Co developed for a flue gas desulfurization (FGD) system. Corrosion tests were carried out in an aggressive solution of 16.9 vol% H2SO4 + 0.35 vol% HCl + Bal. H2O at 60 °C for up to 48 h. The experimental results revealed enrichment of the additional elements (Cu, Sb and Ni) in the corrosion layer, whose concentration increased with test time. As the concentrations of Cu increased, the crystallization and growth of the Cu particles (from several nm to 320 nm)) within the corrosion layer was accelerated. At the initial stage of the test, a continuous amorphous layer rich with the additional elements formed and covered the surface of the steel, which then gradually developed defects, pores and cracks, as the crystallization and growth of Cu particles with the elapse of time. The results indicated that the corrosion resistance of the low alloy steel depends on the existence form of Cu in the corrosion layer, i.e., as solute atoms or as nanoparticles strengthened the corrosion layer and increased corrosion resistance. As the coarsening of Cu particles weakened the corrosion layer and deteriorated the corrosion resistance.