Effect of Chromium and Water Vapor of Low Carbon Steel on Oxidation Behavior at 1050 °C

The high-temperature oxidation behavior of Cr-containing steels are investigated by using continuous thermogravimetric analysis (TGA), in which the coupon samples are exposed at 1050 degrees C in dry and wet air for up to 60 min. The results showed that the oxidation kinetics of Cr-containing steels followed the parabolic law. The phase of oxide scale is examined by X-ray diffraction (XRD), and the surface and cross-sectional morphologies of the specimens after oxidation are studied in detail with scanning electron microscope (SEM) and the electron probe microanalysis (EPMA). Addition of chromium in steel can promote the formation of Fe-Cr spinel layer and Cr2O3 layer to reduce the oxidation rate at high temperatures, especially in dry air. In wet air, the rate of high-temperature oxidation is increased due to the reaction between H2O and FeO, Cr2O3 and Fe, which can generate volatile hydroxide of CrO2(OH)(2) to transform the Fe-Cr spinel from dense layered structure to porous structure. In addition, the amount Cr lost in different steam content is calculated by the classical method of chromium vaporization rates. The oxidation mechanism is proposed based on ions diffusion, chemical reaction, and microstructure of oxide-substrate interface.