The oxide layer on the surface of hot-rolled stainless steel coated plates is usually thick. If it is removed solely 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 steel plates. There are three main pre-treatment methods for pickling:


1. Shot peening

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


2. Alkali leaching treatment

Alkali leaching treatments are respectively oxidative alkaline leaching and reduction alkaline leaching. The oxidative alkali leaching method is also called the "salt bath method". The mechanism is that through alkali treatment, the iron-chromium spinel phase (FeCr2O4) in the oxide layer of the stainless steel coated plate that is difficult to dissolve is modified into a soluble in Alkaline CrO3 causes the oxide layer to fall off due to changes in the structure and volume of the oxide layer. Reduction alkaline leaching uses the strong reducing agent NaH to change the insoluble metal oxides such as iron, nickel, and chromium in the oxide layer back into metals and low-priced oxides, and causes the oxide layer to crack and fall off, thus shortening the pickling time. , improve overall efficiency.

It is worth noting that the stainless steel coated plate will cause a certain degree of Cr6+ pollution during the oxidative alkali leaching process. Reducing alkali leaching treatment can eliminate Cr6+ pollution problem, but its key raw material, NaH, cannot be produced domestically. At present, the most commonly used method in China is the oxidative alkali leaching treatment with potassium permanganate, while the reducing 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 coated plate can continuously change the cathode and anode through the electric field between the cathode and the anode, and remove the surface oxide layer through the action of electric 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 into high-priced soluble ions, thereby dissolving the oxide layer; the first is that the steel matrix of the rust-coated plate is removed The metal in the metal is oxidized into ions, causing the oxide layer attached to the surface to peel off.