Nanostructure of the rust formed on low alloy steels after exposure tests in a high SOx environment

Abstract

Exposure tests were performed on low alloy steels in a high SOx environment, and the structure of the rust was analyzed by TEM (Transmission Electron Microscopy) and Raman spectroscopy. In the exposure test, the concentration of SOx was found to be high, which caused corrosion of the steels. The conventional weathering steel (SMA: 0.6Cr–0.4Cu–Fe) showed lower corrosion weight loss as compared to the carbon steel (SM), and Ni bearing steel exhibited the lowest one. Raman spectroscopy showed that the rusts on Ni bearing steel and SMA were mainly composed of α-FeOOH and spinel oxides. Besides, only Ni bearing steel had no γ-FeOOH in the rust. TEM showed that nano-scale complex iron oxides containing Ni or Cr were formed in the rust on the low alloy steels, which suppressed the corrosion of steels in the high SOx environment.