[en] The carburization behavior of Alloy 800H, Inconel Alloy 617 and Hastelloy Alloy X in helium containing various amounts of H₂, CO, CH₄, H₂O and CO₂ was studied. Corrosion tests were conducted in a temperature range from 649 to 1000⁰C (1200 to 1832⁰F) for exposure time up to 10,000 h. Four different helium environments, identified as A, B, C, and D, were investigated. Concentrations of gaseous impurities were 1500 μatm H₂, 450 μatm CO, 50 μatm CH₄ and 50 μatm H₂O for Environment A; 200 μatm H₂, 100 μatm CO, 20 μatm CH₄, 50 μatm H₂O and 5 μatm CO₂ for Environment B; 500 μatm H₂, 50 μatm CO, 50 μatm CH₄ and < 0.5 μatm H₂O for Environment C; and 500 μatm H₂, 50 μatm CO, 50 μatm CH₄ and 1.5 μatm H₂O for Environment D. Environments A and B were characteristic of high-oxygen potential, while C and D were characteristic of low-oxygen potential. The results showed that the carburization kinetics in low-oxygen potential environments (C and D) were significantly higher, approximately an order of magnitude higher at high temperatures, than those in high-oxygen potential environments (A and B) for all three alloys. Thermodynamic analyses indicated no significant differences in the thermodynamic carburization potential between low- and high-oxygen potential environments. It is thus believed that the enhanced carburization kinetics observed in the low-oxygen potential environments were related to kinetic effects. A qualitatively mechanistic model was proposed to explain the enhanced kinetics. The present results further suggest that controlling the oxygen potential of the service environment can be an effective means of reducing carburization of alloys