Why ASTM 201 stainless steel will rust?

When the surface of stainless steel tube ASTM201 brown rust (point), people great surprise: that 201 stainless steel is not rust, rusty it is not 201 stainless steel, the steel may be a problem. In fact, this is a lack of understanding of the stainless steel one-sided view of the error. Stainless steel will rust under certain conditions a.

ASTM 201 stainless steel resistant to atmospheric oxidation capacity --- namely stainless steel, while also having acid, alkali and salt corrosion medium capacity --- namely corrosion resistance. But the size of the corrosion resistance of steel itself, with their chemical composition, add each state, the use conditions and the type of change in environmental media. Such as 304 stainless steel, in a clean dry atmosphere, there is absolutely excellent anti-corrosion ability, but move it to the waterfront area, contains a lot of salt in the sea of ​​fog, will soon rust; while 316 stainless steel the performance is good. Therefore, not any kind of stainless steel, in any environment corrosion resistant, not rust.

ASTM 201 stainless steel is formed on its surface by the thin layer of fine stable and robust chromium-rich oxide film (protective film), to prevent the continued penetration of oxygen atoms, to oxidation, corrosion resistance capacity is obtained. Once there is some reason, this film was continuously destroyed, air, or oxygen atoms in the liquid will continue to penetrate the iron atom or a metal segregations continuously, the formation of loose iron oxide, the metal surface will be continuously corrosion. The table Mask damaged many forms, more common in everyday life the following categories:

1, ASTM 201 stainless steel surface accumulating the dust containing other metals or heterogeneous metal particles attachments, in the humid air, fixtures and stainless steel condensate between the two together into a micro-cell, triggering a power chemical reaction, the protective film is damaged, known that the electrochemical corrosion.

2, ASTM 201 stainless steel surface adhesion of organic juice (such as vegetables, soup, sputum, etc.), in a case of water oxygen to form organic acids, acids long is the corrosion of the metal surface.

3, ASTM 201 stainless steel surface adhesion containing acid, alkali, salts (such as wall decoration alkaline, lime splash), causing localized corrosion.

4, ASTM 201 stainless steel in a polluted air (such as rich in sulfides, carbon dioxide, nitrogen oxide atmosphere), the case of condensation water to form sulfuric acid, nitric acid, acetic acid solution point, cause chemical corrosion.