Evolution of carbides and chromium depletion profiles during oxidation of Alloy 602 CA

The microstructure evolution in carbide strengthened Alloy 602 CA during exposure to a synthetic flue gas (N2-2.5%O2-8.6%H2O-16.4%CO2) at 1100 °C has been studied. The chromium and aluminium loss resulted in a chromium depleted alloy subsurface area and the dissolution of the carbides within this area. An increase of the carbide fraction in the sample core was observed and quantified. Phase equilibria calculations revealed that the depletion of aluminium as well as that of chromium triggers carbon to leave the depleted area. The overall carbon depletion in that area corresponded to the observed increase in carbide fraction in the sample core.