The hot-rolled strip steel coil produced by the hot-rolling plant is rolled and coiled. The oxide scale generated on the surface of the strip steel under the corresponding conditions can firmly cover the surface of the strip steel and cover the surface of the strip steel. Defects.

From the perspective of steel rolling, if these strips with iron scale are sent directly to the cold rolling mill for rolling, many problems will arise: one is rolling under a large amount of reduction, which will reduce the scale of iron oxide. Into the matrix of the strip steel, affect the surface quality and processing performance of the cold-rolled sheet, and even cause waste; second, the emulsion system entering the cooling and lubricating roll after the iron oxide scale is broken will damage the circulating equipment and shorten the service life of the emulsion; third, damage This is a cold roll with high surface finish and processing accuracy and expensive. Therefore, before the strip is cold rolled, the surface oxide scale must be removed to ensure the surface quality of the produced cold rolled strip.

From the perspective of the production of hot-dip galvanized steel sheets, the use of hot-rolled steel strips for direct hot-dip galvanizing is the same as cold-rolled steel sheets. Before galvanizing, the strip steel must have a clean and active surface. In order to obtain such a surface, the hot-rolled steel strip needs to be treated to remove the oxide scale on the surface, and the usual method is to carry out a pickling treatment.

There are generally two types of iron oxide scale for steel pipes: one is rust, which is an oxide generated by SO2 and CO2 dissolving in moisture in a humid environment at room temperature. This kind of rust layer is reddish brown and is composed of divalent and trivalent iron and oxygen compounds and crystal water; the other is the oxide scale formed at high temperature, commonly known as iron scale, which is dark black or dark brown . It is generated in two situations: one is the rolled iron scale generated during rolling or welding, and the other is the oxide scale generated during the heat treatment process because the oxygen partial pressure is greater than the equilibrium oxygen partial pressure of iron (in the protection Except for annealing in an atmosphere or a reducing atmosphere).

When producing hot-dip galvanized steel pipes, electro-galvanized steel pipes, coated steel pipes or plastic-clad steel pipes, this layer of iron must be removed, otherwise it will have a serious impact on product quality and even fail to produce qualified products. Even if a thin iron sheet exists before galvanizing, it is impossible to plate a complete and continuous zinc layer. During the coating or multi-layer treatment, if the surface oxide is not removed, it will cause bubbling and reduce the corrosion resistance of the coating.

The other most common pickling of steel profiles is the pickling treatment of hot-rolled angle steel (such as for transmission towers) before galvanizing.

For wire, whether it is hot-rolled wire or heat-treated semi-finished steel wire, there is a hard and brittle iron oxide layer on the surface. On the one hand, these iron oxide scales affect the subsequent processing procedures, so that the lubricating coating cannot be firmly combined with the steel substrate; on the other hand, when drawing, because the iron oxide scale is very hard and brittle, it will scratch the surface of the mold and the steel wire. ; In addition, the iron oxide skin is sandwiched between the mold and the steel wire, which will not only increase the friction between the steel wire and the mold, but also increase the friction, and cause wire breakage in severe cases; sometimes the iron oxide skin may be pressed into the steel wire matrix, resulting in coating Defects such as "wing skin" are sometimes produced. Therefore, these iron oxide layers must be removed before the steel wire is drawn.

Similarly for stainless steel and special steel hot-rolled products, pickling treatment is required before cold rolling or cold drawing process. Steel parts and metal products also need to be pickled before surface treatment such as electroplating, phosphating, and coating.