Corrosion Behavior of Fe-Al-Cr Alloys in Sulfur-and Oxygen-Rich Environments in the Presence of Pyrite Available to Purchase

Iron-aluminum-based alloys recently have been considered as weld overlay coatings for corrosion protection. These alloys previously have been shown to possess excellent oxidation and sulfidation resistance when exposed to gaseous environments. Although gaseous corrosion contributes greatly to the total amount of corrosion that can occur during exposure, it has been reported that a solid, reactive slag can accumulate on the boiler tube surface as well. Slag can consist of gaseous corrosion products, unburnt coal particles, and ash from burnt coal. Therefore, to better represent the corrosive conditions in the coal-burning furnace, several Fe-Al-Cr-based alloys were exposed to two reactive gases at 500°C while in contact with reactive pyrite (FeS₂) powder. Two alloys contained Ti additions to determine if these additions would have any beneficial effect on the corrosion behavior of the alloys. Light optical microscopy was used to observe the scales that formed during exposure. Measurements were made of the substrate corrosion layer thickness to quantify the extent of corrosion that occurred. Electron probe microanalysis (EPMA) line scans were used to determine the corrosion layer compositions on selected alloys. Critical alloying contents required to prevent significant substrate corrosion from occurring during the test time were determined. It was found that 19 at% Al was required to prevent significant substrate corrosion from occurring during 100 h of exposure.