Oxidation behavior of Fecralloy and 20/25/Nb stainless steels and a nickel-based alloy, PE16, in argon containing 7 μatm water vapour and 375 μatm hydrogen

The oxidation behavior of four alloys [yttrium-bearing and yttrium-free Fecralloy ferritic stainless steels, a 20/25/Nb austenitic stainless steel and a nimonic alloy, PE16] have been studied in argon (1.3 atm pressure) containing 7 μatm water vapour and 375 μatm hydrogen. The alloys were exposed for periods up to 7166 h at temperatures in the range, 650-1000 0C. The overall reaction kinetics were determined, as were the magnitudes and nature of both the general and any internal attack. The behavior of the alloys in wet argon was consistent with that observed in fully oxidising environments, except at the highest temperature studied, 800 and 1000 0C, with the 20/25/Nb and Fecralloy steels respectively. In carbon dioxide a greater attack of both alloys and a more complex composition of the oxide film on the 20/25/Nb steel had been attributed to its higher oxygen potential compared with that of the H2O/H2 gas mixture. (Auth.)