1, the meaning of stainless steel passivation
The reason why stainless steel is increasingly used is mainly because the series of materials are characterized by corrosion resistance, that is, stainless nature, and stainless steel parts have a long life.
However, the most misunderstood stainless steel is its name - stainless steel. In fact, in the production and processing of stainless steel products, we must also take measures to prevent rust. That is to say, after the finished stainless steel is finished, it must be subjected to surface anti-rust treatment, and after assembly, it can be considered that the processing is completed, and various corrosion accidents can be prevented in the future use.
Where stainless steel parts, such as electroless plating or other coating requirements, are generally passivated before pretreatment (including pickling, black skin, polishing, etc.), in order to be used as finished products or as components. It has been shown that stainless steel can only be permanently passivated for the long-term passive state of the surface, so that the corrosion resistance can be improved.
Both the operational control of the passivation process and the quality inspection of the passivation film are subject to strict specifications.
2, the role of stainless steel passivation
(1) Improve the thermodynamic stability of stainless steel in environmental media. The passivated stainless steel is in a positive position in the metal potential sequence, that is, close to the noble metal, and the chemical property is stable, while the unpassivated stainless steel is in an activated state, at a position where the potential is relatively negative, and is similar to ordinary steel.
(2) Prevent local corrosion of stainless steel. Generally, various corrosion phenomena easily caused by stainless steel, including pitting corrosion, intergranular corrosion, wear corrosion and corrosion fatigue, are related to the surface state. Passivation can eliminate the origin of each corrosion and make the potential of the critical point corrosion positive.
(3) Passivation gives the stainless steel surface sufficient cleanliness. Passivation can remove metal contaminants from the surface layer of stainless steel, as well as impurities embedded in stainless steel, such as copper, zinc, fusible, lead, and low-melting metals, free iron, so that the surface contains chromium and nickel enriched and stabilized. The contamination of these metals is prone to corrosion damage in stainless steel.
(4) Elimination of hot working oxides on stainless steel surfaces. The use of a nitric acid solution containing hydrofluoric acid in the passivation process has the effect of etching the oxide and passivating the surface.
(5) Passivation treatment As a post-treatment, stainless steel is required to have various pretreatments. Passivation treatment is carried out after sandblasting, shot peening, electrochemical polishing and chemical polishing to improve the surface state of the stainless steel.
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