The oxide layer on the surface of the hot-rolled stainless steel coated plate is usually thick. If it is removed only by chemical pickling, it will not only increase the pickling time and reduce the pickling efficiency, but also increase the pickling cost too much. Therefore, other methods need to be used as auxiliary means to pre-treat the steel plate. There are three main pre-treatment methods for pickling:

1. Shot blasting

Shot peening is a widely used mechanical dephosphorization method at present. The principle is to use shot peening equipment to spray fine granular steel shot (sand) to impact the stainless steel coated plate to remove the oxide layer on the steel surface. After the shot peening treatment, part of the oxide layer is removed, and the structure of the remaining oxide layer on the board surface becomes intermittent and loose, which is beneficial to the subsequent pickling process.

2. Alkali leaching treatment

Alkali leaching treatments are oxidative alkaline leaching and reducing alkaline leaching. The oxidation-type alkali leaching is also called “salt bath method”. Alkaline CrO3, and due to the change of the structure and volume of the oxide layer, the oxide layer will fall off. Reduced alkaline leaching is to change the insoluble metal oxides such as iron, nickel, chromium and other insoluble metal oxides in the oxide layer back to metals and low-priced oxides through the strong reducing agent NaH, and make the oxide layer break and fall off, thereby shortening the pickling time , improve the overall efficiency.

It is worth noting that stainless steel clad plates will cause a certain degree of Cr6+ pollution during the treatment process of oxidative alkali leaching. Reduction alkaline leaching treatment can eliminate the problem of Cr6+ pollution, but its key raw material, NaH, cannot be produced in China. At present, the more commonly used method in China is potassium permanganate oxidation type alkali leaching treatment, while reduction type alkali leaching treatment is commonly used abroad.

3. Neutral salt electrolysis

The neutral salt electrolysis process uses Na2SiO4 aqueous solution as the electrolyte. The stainless steel film-coated plate can pass through the electric field between the cathode and the anode, continuously change the cathode and anode, and remove the surface oxide layer through the action of current. The mechanism of the neutral salt electrolysis process is based on the fact that the difficult-to-dissolve oxides of chromium, manganese, and iron in the oxide layer are oxidized to high-priced soluble ions, thereby dissolving the oxide layer; The metal in the battery is oxidized into ions, so that the oxide layer attached to the surface is peeled off.