High-temperature oxidation of industrial FeCrMo steel

The oxidation resistance of Fe-based alloys depends on thin protective film s consisting of the reaction products between the alloy and the atmosphere. An Fe-9Cr-1Mo steel is used as a corrosion-resistant alloy in pressurized water reactors in power generation facilities. The high steam temperature a nd pressure inside the vessel lead to wall thinning in certain areas of the pipe due to erosion corrosion. The pipe's hardness and resistance to corro sion are determined by the composition of the oxide layer, In this study th e samples were taken from pieces of pipe removed after failure that which h ave an operation history of about 20 years, Auger electron spectroscopy was used to measure the segregation and also the influence of oxygen pressure on the oxidation process at 1 X 10(-7) and 5 x 10(-8) Torr over a wide temp erature range. Owing to site competition between the sulphur and oxygen ato ms, the influence of sulphur segregation is more profound at lower oxygen p ressures. According to XPS depth profiles, the oxide layer formed at elevat ed temperatures has a duplex structure consisting of iron and chromium oxid es. Iron oxide is present at the gas/oxide interface, whereas chromium oxid e is closest to the oxide/metal interface, with concentrations that depend on the oxidation temperature: below 400 degrees C the oxide layer consists of Fe2O3 and a small amount of Cr2O3; between 400 and 600 degrees C the oxi de layer consists of a mixture of Fe2O3 and Cr2O3; and above 600 degrees C the layer consists mainly of Cr2O3, Copyright (C) 2000 John Whey & Sons, Lt d.