Stainless steel is a metal with excellent corrosion resistance, but it can still be corroded in some special environments. Therefore, in practical applications, stainless steel often needs to be pickled and passivated to increase its corrosion resistance.
The pickling passivation process is to use strong acid to carry out a chemical reaction on the surface of stainless steel to remove undesirable oxides and impurities on the surface, and then use oxidant to oxidize the surface of stainless steel to form a layer of chromic acid passivation film, so as to improve the corrosion resistance and aesthetics of stainless steel.
The pickling passivation process mainly involves the following steps:
1.Removes iron and organic impurities. Iron and organic impurities are the most common impurities on stainless steel surfaces, and they can affect the oxidation reaction during passivation, so they need to be removed first. The pickling conditions should be strictly controlled, and too strong pickling conditions will lead to a rough surface of the steel.
2.Pickling passivation. The main step of pickling passivation is to soak in a solution of strong acids such as concentrated nitric acid, hydrofluoric acid, sulfuric acid, etc., to remove surface oxides. It is then passivated in a chromic acid passivating agent to form a uniform passivation film on the surface of the stainless steel.
3.Cleaning. The cleaning process is very important, because the residual acids, salts and other substances in the pickling passivation process will cause pollution of the surface of stainless steel and affect its corrosion resistance. Therefore, after the pickling passivation is completed, the stainless steel must be strictly cleaned with water and dilute alkali solution.
4.Dry. After cleaning, the stainless steel needs to be dried to minimize the amount of moisture adsorbed on the surface and thus prevent it from being subjected to secondary contamination.
The pickling passivation process can greatly improve the corrosion resistance and aesthetics of stainless steel, making it suitable for use in harsher environments. However, in the process of pickling passivation, because it involves the use of some strong acids and oxidants, it is necessary to strictly control the pickling conditions to ensure the safety of operators. In addition, pickling passivation also requires reasonable control of the cleaning and drying process to ensure that the stainless steel surface is clean, uniform and complete.