Why is the stainless steel mesh belt also rusty?

When the surface of the stainless steel tube appears brown rust spot (point), people are surprised: think that "stainless steel is not rust, rust is not stainless steel, may be the steel has a problem". In fact, this is the lack of understanding of stainless steel a one-sided wrong view. Stainless steel mesh belt will rust under certain conditions.

Stainless steel has the ability to resist atmospheric oxidation - namely, rust, but also has the ability to corrosion in the medium containing acid, alkali, salt - namely, corrosion resistance. However, its corrosion resistance varies with its chemical composition, mutual state, service conditions and environmental media types. Such as 304 steel pipe, in the dry and clean atmosphere, there is absolutely excellent corrosion resistance, but it will be moved to the coastal area, in the sea fog containing a lot of salt, will soon rust; And 316 steel pipe is good performance. Therefore, not any kind of stainless steel, in any environment can withstand corrosion, not rust. Stainless steel is formed by its surface of a layer of very thin and solid fine stable chromium oxide film (protective film), to prevent oxygen atoms continue to penetrate, continue to oxidize, and obtain the ability to resist corrosion. Once for some reason, this film is continuously damaged, oxygen in the air or liquid will continue to infiltrate or iron atoms in the metal is constantly removed, the formation of loose iron oxide, the gold surface is also subjected to continuous corrosion. This surface film is damaged in many forms, common in daily life are as follows:

1 stainless steel mesh belt surface deposit containing other metal elements of dust or different metal particles attached, in the humid air, the condensate between the attachment and stainless steel, the two connected into a micro battery, triggered an electrochemical reaction, the protective film is damaged, known as electrochemical corrosion.

2 stainless steel surface adhesion organic juice (such as vegetables, soup, sputum, etc.), in the case of water and oxygen, organic acid, organic acid corrosion of metal surface for a long time.

3 stainless steel surface adhesion contains acid, alkali, salt substances (such as decoration of the wall of alkali water, stone ash water splash), cause local corrosion.

4. In the polluted air (such as the atmosphere containing a large number of sulfide, carbon oxide, nitrogen oxide), when condensed water is encountered, sulfuric acid, nitric acid, acetic acid liquid point is formed, causing chemical corrosion.