Oxidation of heat-resistant Fe-base alloy incoloy 800

The oxidation behavior of the heat-resistant Fe-base alloy Incoloy 800 was investigated at around 10000C under oxygen pressures ranging from 1x10-4 to 2x10-1 atm. The rate of oxidation was determined by the weight gain using a Cahn RG Electrobalance. Metallographic, electron microprobe and X-ray diffraction studies of the oxidized specimens were carried out. The rate of oxidation is parabolic, but tends to slightly decrease with the progress of oxidation. Cold rolling of the specimen increased the rate of oxidation. The dependence of the oxidation rate upon oxygen pressure was slightly smaller than that expected when the scale is composed of pure Cr2O3. The oxidized specimen has a layer structure of the outer porous scale, the inner dense scale, the complicated scale-substrate interface region and the internally-oxidized substrate in sequence from the outer side. The outer scale principally contains Cr and Mn, but it also contains smaller quantities of Ti, Fe, Ni, etc. Oxygen partial pressure of the reaction affected the composition of the outer scale. The inner scale is principally composed of Cr2O3. Most of the oxides of Al and Si are present in the scale-substrate interface region and the internally-oxidized substrate region. The existence ratio of the spinel phase against the rhombohedral phase in the outer part of scale increases considerably with the progress of oxidation. (auth.)