1. Overview of pickled products: Pickled steel plates are made of hot-rolled steel coils. After pickling, the surface quality and use requirements of pickled steel plates are intermediate products between hot-rolled steel plates and cold-rolled steel plates. Compared with hot-rolled steel plates, the advantages of pickled steel plates are mainly: good surface quality, high dimensional accuracy, improved surface finish, enhanced appearance effect, and reduced environmental pollution caused by user-dispersed pickling. In addition, compared with hot-rolled products, pickled products are easier to weld because the surface oxide scale has been removed, and are also conducive to surface treatment such as oiling and painting. Generally, the surface quality grade of hot-rolled products is FA, pickled products are FB, and cold-rolled products are FB/FC/FD. Pickled products can replace cold-rolled products to make some structural parts, that is, heat replaces cold.

2. Common defects of pickled steel plates:
The common defects of pickled steel plates in its production process are mainly: oxide scale indentation, oxygen spots (surface landscape painting), waist fold (horizontal fold print), scratches, yellow spots, under-pickling, over-pickling, etc. (Note: Defects are linked to the requirements of standards or agreements. Only those that do not meet the requirements are called defects. For the convenience of expression, defects are used here to replace a certain type of morphology.)
2.1 Iron oxide scale indentation: Iron oxide scale indentation is a surface defect formed during hot rolling. After pickling, it is often pressed in the form of black dots or long strips, with a rough surface, generally with a hand feel, and appears sporadically or densely.
The causes of iron oxide scale are related to many factors, mainly the following aspects: heating in the heating furnace, descaling process, rolling process, roll material, and state, roller state, and rolling plan.
Control measures: Optimize the heating process, increase the number of descaling passes, and regularly check and maintain the roller and roller, so that the rolling line is kept in good condition.
2.2 Oxygen spots (surface landscape painting defects): Oxygen spot defects refer to the dot-shaped, line-shaped, or pit-shaped morphology left after the iron oxide scale on the surface of the hot coil is washed off. Visually, it appears as irregular color difference spots. Because the shape is similar to a landscape painting, it is also called a landscape painting defect. Visually, it is a dark pattern with undulating peaks, which is distributed as a whole or partially on the surface of the strip steel plate. It is essentially an oxidized iron scale stain, which is a layer of things floating on the surface, without a touch, and may be darker or lighter in color. The dark part is relatively rough, and has a certain impact on the appearance after electrophoresis, but does not affect the performance.
Cause of oxygen spots (landscape painting defects): The essence of this defect is that the oxidized iron scale on the surface of the hot-rolled strip is not completely removed, and is pressed into the matrix after subsequent rolling, and stands out after pickling.
Control measures for oxygen spots: reduce the steel tapping temperature of the heating furnace, increase the number of rough rolling descaling passes, and optimize the finishing rolling cooling water process.
2.3 Waist fold: Waist fold is a transverse wrinkle, bend, or rheological zone perpendicular to the rolling direction. It can be identified with the naked eye when unrolling, and it can be felt by hand if it is severe.
Causes of waist fold: Low-carbon aluminum-killed steel has an inherent yield platform. When the steel coil is unrolled, the yield deformation effect occurs under the action of bending stress, which turns the originally uniform bend into an uneven bend, resulting in a waist fold.
2.4 Yellow spots: Yellow spots appear on the part of the strip or the entire steel plate surface, which cannot be covered after oiling, affecting the appearance of product quality.
Causes of yellow spots: The surface activity of the strip just out of the pickling tank is high, the rinsing water fails to play the role of normal rinsing of the strip, and the surface of the strip is oxidized and yellowed; the spray beam and nozzle of the rinsing tank are blocked, and the angles are not equal.
The control measures for yellow spots are: regularly checking the status of the spray beam and nozzle, cleaning the nozzle; ensuring the pressure of the rinsing water, etc.
2.5 Scratches: There are certain depths of scratches on the surface, and the shape is irregular, which affects the surface quality of the product.
Causes of scratches: improper loop tension; wear of nylon lining; poor shape of incoming steel plate; loose coiling of the inner ring of hot coil, etc.
Control measures for scratches: 1) Increase the tension of the loop appropriately; 2) Check the surface condition of the liner regularly, and replace the liner with the abnormal surface condition in time; 3) Repair the incoming steel coil with poor plate shape and loose inner ring.
2.6 Under-pickling: The so-called under-pickling means that the local iron oxide scale on the surface of the strip is not removed cleanly and sufficiently, the steel plate surface is gray-black, and there are fish scales or horizontal water ripples.
Causes of under-pickling: This is related to the process of the acid solution and the surface condition of the steel plate. The main production process factors include insufficient acid concentration, low temperature, too fast strip running speed, and the strip cannot be immersed in the acid solution. The thickness of the hot coil iron oxide scale is uneven, and the steel coil has a wave shape. Under-pickling is usually easy to occur at the head, tail, and edge of the strip.
Control measures for under-pickling: adjust the pickling process, optimize the hot rolling process, control the strip shape, and establish a reasonable process system.
2.7 Over-pickling: Over-pickling means over-pickling. The surface of the strip is often dark black or brownish-black, with blocky or flaky black or yellow spots, and the surface of the steel plate is generally rough.
Causes of over-pickling: Contrary to under-pickling, over-pickling is easy to occur if the acid concentration is high, the temperature is high, and the belt speed is slow. The over-pickling area should be more likely to appear in the middle and width of the strip.
Control measures for over-pickling: Adjust and optimize the pickling process, establish a suitable process system, and carry out quality training to improve the quality management level.

3. Understanding of quality management of pickled steel strips
Compared with hot-rolled steel strips, pickled steel strips only have one more pickling process. It is generally believed that it should be easier to produce pickled steel strips with qualified quality. However, practice shows that to ensure the quality of pickled products, not only the pickling line should be in good condition, but also the production and operation status of the previous process (steelmaking and hot rolling process) should be kept stable so that the quality of hot-rolled incoming materials can be guaranteed. Therefore, it is necessary to adhere to a consistent quality management method to ensure that the quality of each process is in a normal state to ensure the quality of the final product.