Morphology of Oxide Scale and Oxidation Kinetics of Low Carbon Steel

The oxidation kinetics and composition of oxide scales on low carbon steel (SPHC) were studied during isothermal oxidation. Thermogravimetric analyzer (TGA) was used to simulate isothermal oxidation process of SPHC for 240 min under air condition, and the temperature range was from 500 to 900 °C. Scanning electron microscope (SEM) was used to observe cross-sectional scale morphology and analyze composition distribution of oxide scales. The morphology of oxide scale was classical three-layer structure. Fe2O3 developed as whiskers at the outermost layer, and interlayer was perforated-plate Fe3O4 while innermost layer was pyramidal FeO. From the oxidation curves, the oxidation mass gain per unit area with time was of parabolic relation and oxidation rate slowed down. On the basis of experimental data, the isothermal oxidation kinetics model was derived and oxidation activation energy of SPHC steel was 127.416 kJ/mol calculated from kinetics data.