During the production of common carbon hot-rolled steel strips, a layer of iron oxide scale easily forms on the surface. If this scale is not effectively removed, it will directly affect the quality of subsequent processing and product performance. The iron oxide scale mainly consists of three layers: the innermost layer is fulminate, a solid solution of FeO and Fe3O4; the middle layer is Fe3O4; and the outermost layer is Fe2O3. These three layers have different densities and chemical properties. fulminate, due to its higher porosity, is relatively easy to remove, while Fe3O4 and Fe2O3, due to their denser structure, are more difficult to remove.
Methods for removing iron oxide scale from the surface of common carbon hot-rolled steel strips are mainly divided into two categories: mechanical descaling and chemical descaling. Mechanical descaling breaks or peels off the iron oxide scale through physical action. Common methods include grinding with a grinding wheel, bending and stretching to break the scale, and shot peening. Grinding with a grinding wheel is suitable for removing localized iron scale, but it is inefficient and easily damages the steel strip surface. Bending and stretching descaling breaks down the iron oxide scale during the stretching and bending process of the strip, and is often used in conjunction with pickling to improve the overall descaling effect. Shot peening uses high-speed jets of fine iron beads to impact the steel strip surface, breaking down and removing the iron oxide scale; it is also often combined with pickling to accelerate the descaling process and improve quality.
Chemical descaling utilizes the chemical reaction between iron oxide scale and acid to dissolve and remove the scale. While this method can thoroughly remove iron scale, it is time-consuming and can easily lead to localized over-acidification or incomplete scale removal on steel strips with uneven scale thickness. Therefore, in actual production, chemical descaling is often used in combination with mechanical descaling to leverage the advantages of each and improve the overall descaling effect. For example, mechanical descaling can be used first to break down the iron oxide scale, followed by pickling to thoroughly dissolve any remaining scale, thus ensuring the surface quality of the steel strip.
To prevent the formation of iron oxide scale on the surface of common carbon hot-rolled steel strips, it is necessary to optimize the heating and rolling process. By rationally controlling the slab heating temperature, heating time, and soaking zone temperature, the oxidation time of the steel billet at high temperatures can be reduced, thereby decreasing the amount of iron oxide scale formed. Simultaneously, optimizing the rolling speed and cooling rate, allowing the steel strip to complete the rolling process at the lowest possible temperature and the highest possible rolling speed, can further reduce the thickness of the iron oxide scale. For example, in terms of final rolling temperature control, lowering the final rolling temperature can slow down the oxidation rate, thereby reducing iron oxide scale formation; in terms of cooling rate control, rapid cooling methods such as laminar flow cooling can quickly reduce the surface temperature of the steel strip, reducing the time for iron oxide scale formation.
Furthermore, equipment maintenance and precise control of process parameters are equally crucial for preventing iron oxide scale formation. Regularly inspecting and replacing descaling nozzles, and cleaning the descaling pump and motor, can ensure stable pressure and uniform impact force in the descaling system, thereby improving the descaling effect. Meanwhile, establishing reasonable roll changing cycles and side guide plate inspection systems can prevent oxide scale indentation defects caused by roll aging or side guide plate wear. For example, shortening the finishing roll changing cycle and strengthening the inspection and maintenance of roll cooling water nozzles can maintain good roll surface quality and reduce oxide scale formation and roll sticking.
In the subsequent processing of common carbon hot-rolled steel strip, if oxide scale indentation defects are found, the oxide scale can be removed by appropriately increasing the pickling time and optimizing pickling process parameters. During pickling, the acid penetrates the metal surface through cracks and pores in the oxide scale layer, reacting with metallic iron and fulminate to generate sulfates or chlorides soluble in the acid, thereby causing the oxide scale to detach from the steel strip surface.
