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Pickling pretreatment of stainless steel industrial plate

Pickling pretreatment of stainless steel industrial plate

The oxide layer on the surface of stainless steel industrial plates 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 greatly increase the cost of pickling. Therefore, it is necessary to use other methods as auxiliary means to pre-treat the steel plate. There are three main pretreatment methods for pickling:

1. Shot Peening

Shot peening is currently a very widely used mechanical dephosphorization method. The principle is to use shot blasting equipment to spray fine-grained steel shots (sand grains) to hit the steel to remove the oxide layer on the surface of the stainless steel industrial plate. After sandblasting, part of the oxide layer is removed, and the remaining oxide layer structure on the surface of the board becomes discontinuous and loose, which is beneficial to the subsequent pickling process.

2. Alkali leaching treatment

Alkali leaching treatment is divided into oxidation type alkaline leaching and reduction type alkaline leaching.

Oxidized alkaline leaching is also called “salt bath method”. The mechanism is to modify the insoluble iron chromium spinel phase (FeCr2O4) in the oxide layer of the stainless steel industrial plate by alkali treatment to alkali-soluble CrO3, and the oxide layer, structure and volume changes promote the shedding of the oxide layer . The reduction type alkaline leaching is to reduce the iron, nickel, chromium and other insoluble metal oxides in the oxide layer to metal or low-valent oxides through the strong reducing agent NaH, and the oxide layer is broken and peeled off, shortening the pickling time.

During the oxidative alkaline leaching process, a certain degree of Cr6 pollution will be produced. The reduction type alkaline leaching treatment can eliminate the Cr6 pollution problem. At present, oxidizing alkali immersion is very common in the pickling of stainless steel industrial plates.

3. Neutral salt electrolysis

The neutral salt electrolysis process uses Na2SiO4 aqueous solution as the electrolyte. The stainless steel industrial plate continuously changes the cathode and the anode through the electric field between the cathode and the anode, and removes the surface oxide layer through the action of the current. The mechanism of the neutral salt electrolysis process is based on the fact that insoluble oxides of chromium, manganese and iron in the oxide layer are oxidized into high-valent soluble ions, thereby dissolving the oxide layer. The other is based on the oxidation of the metal in the stainless steel matrix, which is an ion, so the oxide layer attached to the surface will peel off.

In summary, the pretreatment process of pickling is mainly to remove, dissolve and strip the oxide layer on the surface of the stainless steel industrial plate, which can reduce the load in the pickling process.