Why stainless steel will rust?

Let me talk about why the rust stainless steel, stainless steel and then say Why will rust?

 

Stainless steel does not rust easily have a great relationship with the ingredient of stainless steel. Stainless steel components in addition to iron, there are chromium, nickel, aluminum, silicon and the like. General stainless chromium content is generally not less than 12%, even up to 18% higher. After adding chromium steel and other elements, you can change the properties of steel, such as a more uniform molecular structure example steel, in steel surface easier to generate a dense layer of protective oxide film, thus greatly improving the ability of corrosion-resistant stainless steel. Therefore, stainless steel is resistant to fire, water, acid, alkali and various solutions to its corrosion, no rust. Scientists have discovered that the more uniform internal structure of steel, various components on the more close contact, corrosion invasion more difficult, plus a layer of oxide on the surface and attached to the protective film, like to put on armor, like iron and steel, natural not easy to rust.

 

? Why are rusting stainless steel tube when the surface of brown rust (points), people great surprise: that "Stainless steel is not rust, rust is not stainless steel, the steel may be a problem." In fact, this lack of understanding is a stainless steel one-sided view of the error. Stainless steel under certain conditions will be rusty.

Stainless steel has the ability to resist atmospheric oxidation of stainless steel --- namely, while also having acid, alkali, salt corrosion medium capacity --- that is corrosion resistance. But its size is corrosion resistance of steel itself with its chemical composition, plus mutual status, conditions of use and environmental media type change. Such as 304 steel, in a clean dry atmosphere, there is absolutely excellent anti-corrosion ability, but to move it to the waterfront, contains a lot of salt in sea mist, and will soon be rusty; and 316 steel is manifested good. Thus, rather than any kind of stainless steel, in any environment corrosion resistant, not rust.

 

 

Stainless steel is extremely thin and fine solid stable chromium-rich oxide film (protective film) formed by its surface, to prevent the continued infiltration of oxygen atoms, to oxidation, to obtain resistance to rust. Once there is some reason, this film was constantly undermined, air or liquid oxygen atoms will continue to infiltrate or metal from iron atoms constantly analyze it, to form a loose iron oxide, metal surface rust will continue to suffer. This lot proforma mask damaged in daily life common are the following categories:

1. Stainless steel surface accumulating the attachments contain other metal elements or heterogeneous metal dust particles, in the humid air, condensate and stainless steel fixtures between the two together into a micro-battery, causing the electrochemical reaction , the protective film is damaged, called a electrochemical corrosion.

2. Stainless steel surface adhesion of organic juice (such as vegetables, soup, sputum, etc.), in the case of water oxygen to form organic acids, organic acids for a long time the corrosion of metal surfaces.

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

4. In the air pollution (such as with a lot of sulfide, carbon dioxide, nitrogen oxide atmosphere), the case of condensed water to form sulfuric acid, nitric acid, acetic acid solution point, causing chemical corrosion.