The role of stainless steel pickling
The purpose of pickling stainless steel is to remove the oxide film on the surface of stainless steel. After pickling, a dense oxide film is formed on the surface of stainless steel. This process is called pickling passivation. This film is the key to preventing stainless steel from rusting and corroding in general media. Therefore, stainless steel does not necessarily need to be pickled. It is only necessary if there is oxide scale on the surface.
Stainless steel pickling is often associated with passivation. Generally, stainless steel that requires pickling must be passivated, because no passivation film is formed on the surface after pickling or the thickness of the passivation film formed is very thin and does not have any effect. Add a subsequent passivation process to form and improve the passivation film on the stainless steel surface. For example, annealing under protective atmosphere such as pure hydrogen, ammonia decomposition, etc. does not require pickling.
One of the purposes of pickling is to create conditions for passivation treatment and ensure the formation of a passivation film. Because an average of 10um thick layer of the stainless steel surface is corroded through pickling, the chemical activity of the acid makes the dissolution rate of defective parts higher than other parts on the surface, so pickling can make the entire surface even and balanced, some of the original Hidden dangers that could easily cause corrosion are eliminated.
But more importantly, through pickling and passivation, iron and iron oxides are dissolved preferentially than chromium and chromium oxides, and the chromium-poor layer is removed, causing chromium to be enriched on the surface of stainless steel. This chromium-rich passivation film The potential can reach +1.0V (SCE), which is close to the potential of precious metals, improving the stability of anti-corrosion. Different passivation treatments will also affect the composition and structure of the film, thereby affecting the rust resistance. For example, through electrochemical modification treatment, the passivation film can have a multi-layer structure, forming CrO3 or Cr2O3 in the barrier layer, or forming a glassy state. The oxide film enables stainless steel to exert greater corrosion resistance.
GNEE Steel Group is China's professional one-stop supply chain enterprise for steel products. Its stainless steel pipe production technology has reached the world's average technical level. It has been recognized by dozens of project companies and has become a star enterprise in Asia.
