Cyclic carburization-oxidation behavior of Hastelloy-X at 1000°C

Cyclic corrosion, consisting of carburization in Ar + 4% CH4 + 3% H-2 for 1 h and oxidation in air for 1 h, of Ni-base in a wrought alloy, Hastelloy-X, was investigated at 1000 degrees C to understand the significant metal loss occurring in fuel injection nozzles of gas turbine combustor operated using natural gas. The mass gain of cyclic corrosion was relatively low up to about eight cycles of corrosion by formation of a Cr2O3 scale in each oxidation stage, but it increased rapidly due to formation of a Fe- and Ni-rich oxide scale as the number of corrosion cycles increases. The Cr content in the subsurface region rapidly decreased under the cyclic corrosion condition compared with a continuous single oxidation or carburization, which resulted in the formation of non-protective Fe- and Ni-rich oxide scale in a small number of corrosion cycles. The formation of a Cr3C2 scale from the protective Cr2O3 scale in the carburization stage was detrimental for the oxidation resistance of Hastelloy-X and was considered to have a similar effect to spallation of a Cr2O3 scale; therefore, it accelerated Cr consumption from the alloy subsurface region.