Types and causes of surface defects caused by pickling of stainless steel plates

In the production and processing of stainless steel plates, the pickling process is indispensable, but sometimes pickling will cause various defects on the surface of the stainless steel plate. In order to prevent the formation of defects, it is necessary to have a clear understanding of the reasons for their formation, so as to maximize the success rate of pickling.

The surface defects that are prone to appear during the pickling process of stainless steel plates and the reasons for their formation are as follows.
One is pickling bubbles, which are caused by the formation of hydrogen gas from the acid and the exposed stainless steel plate metal. When it is cold-rolled, it will produce a crackling explosion, characterized by small strip-shaped bubbling, and it will appear as black fine cracks after rupture. After rolling, the bubble cracks will extend and expand, thereby reducing the mechanical properties of the stainless steel plate.
The formation mechanism of pickling bubbles is that when the stainless steel plate forms a chemical reaction with acid, some hydrogen atoms are generated, which penetrate into the crystal lattice of the stainless steel plate and deform it. After the material is deformed, the hydrogen will diffuse into the metal. Hydrogen atoms pass through the metal and are molecularized, and escape from the acid solution. The molecularization of part of the hydrogen atoms is carried out on the boundary of the microscopic pores generated by the lattice deformation, or in the inclusions and pores of the metal. The hydrogen in the pores The pressure can reach tens of megapascals, causing internal stress that causes hydrogen embrittlement to be generated in the stainless steel plate.
The way to prevent it is to adjust the concentration of the acid solution, control the temperature of the solution during pickling and the flatness of the surface of the stainless steel plate, etc.
The second is pickling. The phenomenon that the stainless steel plate stays in the acid solution for too long will make its surface gradually become rough and pockmarked under the action of the acid solution, which is called over pickling.
This defect will greatly weaken the elongation performance of the stainless steel plate. During the rolling process, the stainless steel plate is very easy to break and break, and cause sticking to the roll. Even if the pickled stainless steel plate is rolled, it cannot be regarded as a finished product, because its mechanical properties are greatly reduced.
The reason for the pickling is that the continuous operation of the unit is interrupted, so that the pickling loses its continuity, or the processing time is too long due to the broken strip of the strip. The prevention method is to pay attention to the operation coordination of the whole unit as much as possible to ensure that the production can go on normally.
The third is due to pickling. After the stainless steel plate is pickled, there will be some uncleaned iron oxide scales on the surface, which is called under pickling. For stainless steel plates that are not pickled, the surface of the stainless steel plate will be dark or face-shaped after rolling if it is light; if it is serious, the oxide scale will be pressed in and appear black spots. In addition, the elongation performance of the oxide scale is relatively poor, so after rolling, the stainless steel plate will have defects such as waves or buckling due to uneven elongation. The reason for under-pickling is that the thickness of the oxide scale is uneven, and the thicker part of the oxide scale requires a longer pickling time, and the iron oxide in it decomposes into relatively insoluble Fe2O3; the waviness of the stainless steel plate is compared with the camber Large, during the pickling process, the wavy part or bent part is not soaked in the acid solution, resulting in pickling leakage.