Formation of Black Striped Oxide Scale on Hot-Rolled Si-Containing Carbon Steel

The black striped oxide scale formed on silicon (Si)-containing hot-rolled carbon steel sheets was investigated. The small black stripes of oxide scale became band shaped as the flow used in mill cooling was increased. The distance between the black oxide scale bands was the same as that of the overlapping areas in the hydraulic descaling system. The average thickness of the black striped oxide scale was larger than that of the normal scale region. No ferric oxide (Fe2O3) was observed in the scale, particularly in the fractured parts of the black striped oxide scale. Furthermore, Si did not obviously accumulate in the black striped oxide scale, indicating that the oxide scale was not induced by the residual secondary scale generated during rough milling. The cooling conditions in finish milling affected the deformability of the scale in the overlapping areas. Consequently, the difference in thickness between the overlapping areas and adjacent regions led to the formation of the black striped oxide scale.