The corrosion resistance of stainless steel is mainly due to the surface covered with a very thin (about 1 nm) dense passivation film, which is a basic barrier for stainless steel protection. The passivation of stainless steel has dynamic characteristics and should not be regarded as a complete stop of corrosion, but a barrier to diffusion, which greatly reduces the reaction speed of the anode. It is generally preferred to destroy the membrane in the presence of a reducing agent such as chloride, and to retain or repair the membrane in the presence of an oxidant such as air.
The stainless steel workpiece placed in the air will form an oxide film, but the film is not sufficiently protective. It is usually thoroughly cleaned, including alkaline and pickling, followed by passivation with an oxidizing agent to ensure the integrity and stability of the passivation film. One of the purposes of pickling is to create favorable conditions for the passivation treatment to ensure the formation of a good quality passivation film. Because the surface of the stainless steel surface is etched by an average of 10 μm thick by pickling , the chemical activity of the acid solution makes the dissolution rate of the defect portion higher than other parts on the surface, so the pickling can make the entire surface tend to be evenly balanced. Hidden dangers that are likely to cause corrosion are removed. But more importantly, by acid passivation passivation, the iron and iron oxides are preferentially dissolved than the chromium and chromium oxides, and the chromium-depleted layer is removed, causing chromium to be concentrated on the stainless steel surface. This chromium-rich passivation film The potential is up to +1.0V (SCE), close to the potential of the precious metal, improving the stability of corrosion resistance. Different passivation treatments also affect the composition and structure of the film, thereby affecting the rust. For example, by electrochemical modification, the passivation film can have a multilayer structure, form CrO3 or Cr2O3 in the barrier layer, or form a glassy state. The oxide film allows the stainless steel to exhibit maximum corrosion resistance.
Degreasing and degreasing----flushing water----activation---flushing water----passivation----flushing water----neutralization----flowing water rinse Clean----Pure pure water----dry packaging
Process description :
1. Degreasing, if you are sure that the surface of the workpiece is free of any oil, you can omit this step.
2. Activation, soaking time is 2-5 minutes, if you are sure that the surface of the workpiece does not have any rust, solder spots and other impurities (such as just polished workpiece), you can omit this step.
3. Passivation, must pass the process. The soaking time is 30 minutes. The longer the time, the more complete the passivation film.
4. Neutralize, soaking time is 3 minutes. If the surface shape is simple, there is no crepe, no blind holes, this step can be omitted.
5. Passing pure water, it must pass the process , the time is 3 minutes.
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