High Temperature Oxidation of Steel; New Description of Structure and Properties of Oxide

The quality of steel sheets is strongly affected by the surface defects that can be generated during hot rolling and are often related to scales removal operation. These defects are related to rather complex high temperature oxidation processes. In order to reduce an occurrence of the defects, it is necessary to understand better the formation of iron oxides during high temperature oxidation, the structure of the interfaces with the substrate and between different oxide phases. However, due to the lack of good experimental research tools details of iron oxide microstructures were not investigated. Conventional methods, such as backscattered electron images or fractography can only provide general characteristics of microstructures like grain morphology and grain size. In this paper the microstructure, phase distribution and texture in oxide formed during high temperature oxidation of iron and low carbon steels are investigated. The oxide microstructures are characterized by orientation imaging microscopy (OIM) on the cross-sectional area of the oxide layers. It is demonstrated that OIM using electron backscattered diffraction (EBSD) techniques, can be used to distinguish grains having different phase composition and orientation and can become invaluable tool for visualizing the oxide microstructure, texture and also can be used to study oxide defects. The three different iron oxides phases can be distinguished and the characteristics of oxides with different oxidation histories compared The characteristics of high temperature oxidation microstructure of iron are presented with description of iron oxide defects and cracking as well as the illustration of the interfacial microstructure between the layered iron oxides.