Carburization of three Fe-19Ni-21Cr-xAl (x = 0, 2, 6 at.%) alloys at 900 °C in oxygen-contaminated CH4/H2 atmospheres

• Alloys with 0 & 2 at.% Al in 10% CH4/H2 formed double internal carburization.
• Alloys with 0 & 2 at.% Al in 1.57% CH4/H2 formed single internal carburization.
• Al addition to the Fe-19Ni-21Cr alloys was beneficial to reduce carbon attack.
• Addition of 6 at.% Al did not inhibit carburization and metal dusting.
• A model for internal oxidation of ternary alloys used to describe internal attack.

The corrosion of three Fe-19Ni-21Cr-xAl (x = 0, 2, 6 at.%) alloys was studied at 900 °C in 10% CH4/H2 and 1.57% CH4/H2. All alloys followed complex kinetics. Addition of 2 at.% Al had a slight effect on the corrosion behavior, while that of 6 at.% Al reduced the carbon attack, but was still insufficient to form protective Al2O3 scales. The concept of virtual carbon activity was applied to examine the deviation from equilibrium of the methane decomposition reaction. Moreover, a treatment of internal oxidation of ternary alloys was used to describe the internal carburization kinetics.