Stainless steel plate pickling pretreatment process

The oxide layer on the surface of the hot-rolled stainless steel sheet is usually thick. If it is simply removed by chemical pickling, it will not only increase the pickling time, reduce the pickling efficiency, but also excessively increase the pickling cost. Therefore, other methods are needed as an aid to pre-treating the steel sheet. There are three main pretreatment methods for pickling:

1, shot peening

Shot peening is currently the most widely used method of mechanical phosphorus removal. The principle is to use the blasting equipment to spray fine granular steel shots (sand) to impact the steel to remove the oxide layer on the steel surface. After the shot peening, part of the oxide layer is removed, and the structure of the remaining oxide layer on the surface of the sheet becomes loose and loose, which facilitates the subsequent pickling process.

2, alkaline leaching treatment

The alkali leaching treatment is divided into oxidized alkali leaching and reduced alkali leaching.

Oxidation type alkali leaching is also called "salt bath method", and its mechanism of action is to change the insoluble iron chrome spinel phase (FeCr2O4) in the stainless steel oxide layer to alkali-soluble CrO3 by alkali treatment, and due to the oxide layer. Changes in structure and volume cause the oxide layer to fall off. The reduced alkali leaching is to reduce the hardly soluble metal oxides such as iron, nickel and chromium in the oxide layer to metal or low-valent oxide by the strong reducing agent NaH, and to break the oxidized layer, shorten the pickling time and improve effectiveness.

During the oxidizing type alkaline leaching treatment, a certain degree of Cr6+ contamination is generated. Reduced alkali leaching treatment can eliminate the problem of Cr6+ pollution, but the key raw material NaH is not produced in China. At present, domestically used potassium permanganate oxidized alkaline leaching treatment, while the domestic use of reduced alkali leaching treatment.

3. Neutral salt electrolysis

The neutral salt electrolysis process uses Na2SiO4 aqueous solution as the electrolyte, and the stainless steel plate passes through the electric field between the cathode and the anode, continuously transforms the cathode and the anode, and removes the surface oxide layer by the action of current. The mechanism of the neutral salt electrolysis process is based on the oxidation of insoluble oxides of chromium, manganese and iron in the oxide layer into high-soluble soluble ions, so that the oxide layer is dissolved; first, the metal in the stainless steel matrix is oxidized. It is an ion, so that the oxide layer attached to the surface is peeled off.

The neutral salt electrolysis process is one of the most widely used pretreatment processes.

In the case of the integrated body, the pre-washing treatment process is mainly for the removal, dissolution and stripping of the surface oxide layer of the hot-rolled stainless steel sheet, which can reduce the load during pickling.

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