High temperature corrosion of superheater steels by KCl and K2CO3 under dry and wet conditions

The influence of both solid KCl and solid K2CO3 on the oxidation behavior of a ferritic 10CrMo type steel and a nickel-based Alloy 625 type steel was investigated in the laboratory. Samples were exposed for a week at temperatures of 500 °C, 550 °C, and 600 °C. The role of water vapor was also studied by carrying out exposures under two different atmospheres: dry air, and air with a water content of 30%. Analyses were performed with SEM/EDXA to determine the extent of corrosion, the elemental distribution, and the identification of corrosion products. alts were found to be corrosive towards both steels, but the influence of KCl was significantly greater than that of K2CO3. In terms of durability, Alloy 625 exhibited higher corrosion resistance than 10CrMo. In the case of 10CrMo, the oxide formed always consisted of iron oxide with a chromium-rich region near the original steel surface. In the case of Alloy 625, the oxide consisted mainly of nickel oxide when it formed in the presence of KCl, and chromium oxide when it formed in the presence of K2CO3.