The current study investigated the heat treatment of oxide scale on hot-rolled strip and its effect on strip pickling. Based on this investigation, the following conclusions can be made:The oxide scale at the center regions of hot-rolled strip can be successfully modified under continuous heating and cooling conditions. By heating the scale, either in air or in nitrogen at a rate of 600 deg C/minute to a target temperature in the range of 680 to 700 deg C, followed by rapid cooling at a rate of about 1,200 deg C/minute to 580 deg C, a substantial amount of the scale is converted to wustite. The wustite phase formed can be retained to room temperature at a cooling rate of 30 deg C/minute from 580 deg C.If the target temperature increases to above 720 deg C, the entire scale layer is transformed to wustite if the heat treatment is conducted in nitrogen. An outer layer of magnetite, and presumably an extremely thin surface layer of hematite, form when the heat treatment is conducted in air.When the heat treatment is conducted in nitrogen with a target temperature above 700 deg C, there is an improvement in pickling rate of 20 to 25 percent.When the heat treatment is conducted in air, the improvement is about 10 to 15 percent when the target temperature is 680 to 700 deg C. However, the beneficial effect is reduced by the additional formation of oxide during the treatment when the target temperature is too high (e.g., 780 deg C).
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