The sulfidation/oxidation of Armco iron-based superalloys between 1023 and 1373 K

The sulfidation/oxidation of two Armco iron-based superalloys has been studied at temperatures between 1023 and 1373 K using SO2/O2 atmospheres. At the lower temperature range, the reaction kinetics conform to the parabolic rate law. At temperatures greater than 1173 K, paralinear behavior must be taken into account due to further reaction of Cr2O3 to form the volatile product CrO3. Armco 18SR-C is the best among the Armco 18SR alloys studied because of its ability to form a Cr2O3 protective layer. The presence of about 2 pct Al in Armco 18SR reduces the parabolic rate constant by an order of magnitude. Armco T310 with nickel is not protective at higher temperatures due to the formation of low melting sulfides. The kinetic information obtained from both parabolic and volatilization rate data is represented by an Arrhenius equation. Mass transfer correlations were used to predict the volatilization rate from the experimental conditions in the present study and from other literature data. Although wide hydrodynamic conditions were encountered, fairly good predictions were obtained