Initial Stage of Oxidization of Silicon Electrical Engineering Steel in the Air in a Temperature Range of 360–740 °С

Abstract

Kinetics of the initial stage of oxidation of the silicon electrical engineering steel is studied using methods of colour indication and X-ray spectral microanalysis. It was found that the oxidation rate is determined by diffusion processes for both iron and steel. Iron oxidation is described by the parabolic equation h = kt, whereas for steel the equation has the form h = K ln t + b. Activation energy of the process equals to 48.049±0.1 kJ·mole^–1 in the temperature range of 520–570 °C and 196.359 ± 0.1 kJ·mole^–1 in the range of 580–600 °C. The increase of activation energy is due to the wustite appearing in the oxide layer. Oxidation activation energy of electrical engineering steel equals to 6.770 kJ·mole^–1 below ~ 530 °C and to 12.880 kJ·mole^–1 above 560 °C. The rate of steel oxidation is much lower than that of iron. This is explained by the formation on the steel surface of the protective oxide coating containing binary oxides like Fe2SiO4.