Isothermal Structure Transformation and Kinetics Behavior of Oxide Scale on Low Carbon Steel

The phase transformation of the oxide scale that forms on hot-rolled steel strips during cooling is one of the most important phenomena, which determines the surface quality of the strips, because the properties of the oxide scale, such as spallation resistance, crack initiation, and propagation, and pickling behavior, are strongly dependent on the oxide scale microstructure. To obtain steel strips with high surface quality, it is crucial to understand the microstructural development of the oxide scale. In this paper, a thermogravimetric analyzer was used to study the isothermal structure transformation behavior of FeO formed at high temperature in an inert gas (Ar) at 300-550 degrees C for 1 000-15 000 s. Meanwhile, the isothermal dynamic model of FeO eutectoid transformation was established based on the JMAK equation combined with experimental data. The experimental results show that the oxide scale structure of the sample after pre-oxidation is composed of Fe2O3, Fe3O4, and FeO. At 300 degrees C and 550 degrees C, only the pro-eutectoid structure is formed in the oxide scale, but no eutectoid structure is formed. When the isothermal temperature is in the range of 350-500 degrees C, both pro-eutectoid structure and eutectoid structure are formed in the oxide scale. With the extension of isothermal time, the eutectoid reaction continues until the complete decomposition of FeO. In addition, the FeO eutectoid transformation isothermal dynamics model was used to predict the eutectoid structure content of FeO eutectoid decomposition under different isothermal conditions, and the experimental data were compared with the predicted results, which verified the high prediction accuracy of the model.