A Comparison of Texture Development in an Experimental and Industrial Tertiary Oxide Scale in a Hot Strip Mill

Electron backscatter diffraction (EBSD) has been used to investigate the microstructure and texture-based features of an industrial tertiary oxide scale formed on a micro-alloyed low-carbon steel from a hot strip mill. EBSD-derived maps demonstrate that the oxide scale consists primarily of magnetite (Fe₃O₄) with a small amount of hematite (α-Fe₂O₃) which scatters near the surface, at the oxide/steel interface and at the cracking edges. The results extracted from these maps reveal that there is a significant difference between the industrial and the laboratory oxide scales in their grain boundaries, phase boundaries, and texture evolutions. There are high proportions of special coincidence site lattice boundaries Σ3 and Σ13b in the magnetite of the industrial oxide scale, rather than the lower orders of Σ5, Σ7, and Σ17b, which develop in the experimental oxide scale. Within the phase boundaries, the orientation relationships between the magnetite and the hematite correspond to the matching planes and directions {111}Fe₃O₄||{0001}α-Fe₂O₃ and {110}Fe₃O₄||{110}α-Fe₂O₃. Magnetite in both of these oxide scales develops a relatively weak {001} fiber texture component including a strong {001}〈100〉 cube and a slightly strong {100}〈210〉 texture components. Unlike the {001}〈110〉 rotated cube component in the experimental oxide scale, the magnetite in the industrial tertiary oxide scale develops a strong {112}〈110〉 and a relatively strong {113}〈110〉 and {111}〈110〉 texture components. These findings have the potential to provide a convincing step forward for oxidation research.