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Why is stainless steel rusty?

2017-08-02

Why is stainless steel rusted? When brown rust spots (dot) appear on the surface of stainless steel pipes, people are surprised: "Stainless steel is not rusted, rust is not stainless steel, and steel may be a problem." In fact, this is a one-sided misconception about the lack of understanding of stainless steel. Stainless steel will also rust under certain conditions.

Stainless steel has the ability to resist atmospheric oxidation - that is, rust, and also has the ability to corrode in acids, alkalis, and salts - that is, corrosion resistance. However, the degree of corrosion resistance varies with the chemical composition of the steel itself, the state of interaction, the conditions of use, and the type of environmental medium. For example, 304 steel pipe has absolutely excellent rust resistance in a dry and clean atmosphere, but it is moved to the coastal area, and it will soon rust in sea fog containing a lot of salt; while 316 steel pipe will perform. good. Therefore, it is not any kind of stainless steel that is resistant to corrosion and rust in any environment.

Stainless steel is a very thin and strong and stable chromium-rich oxide film (protective film) formed on the surface to prevent the oxygen atoms from continuing to infiltrate and continue to oxidize, thereby obtaining the ability to resist rust. Once for some reason, the film is continually destroyed, oxygen atoms in the air or liquid are continuously infiltrated or iron atoms in the metal are continuously separated to form loose iron oxide, and the surface of the metal is continuously rusted. This type of surface film is destroyed in many forms, and the following are common in daily life:

1. The surface of the stainless steel contains dust or other metal particles attached to other metal elements. In humid air, the condensed water between the attached material and the stainless steel connects the two into a micro battery, triggering an electrochemical reaction. The protective film is destroyed, which is called electrochemical corrosion.

2. The surface of the stainless steel adheres to the organic juice (such as melon, noodle soup, glutinous rice, etc.), and in the case of water and oxygen, it constitutes an organic acid, and the organic acid corrodes the metal surface for a long time.

3. The surface of the stainless steel adheres to acid, alkali and salt substances (such as alkali water and stone water splashing on the wall), causing local corrosion.

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

All of the above can cause the corrosion of the stainless steel surface protective film to cause rust. Therefore, in order to ensure that the metal surface is permanently bright and not rusted, we recommend:

1. The surface of the decorative stainless steel must be cleaned and scrubbed frequently to remove the deposits and eliminate external factors that cause modification.

2. 316 stainless steel is used in the coastal area, and 316 is resistant to seawater corrosion. 3. Some stainless steel tube chemical components in the market can not meet the corresponding national standards, and can not meet the 304 material requirements. Therefore, it will also cause rust, which requires the user to carefully select the products of reputable manufacturers.


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Kunshan Minglida Stainless Steel Co., Ltd.

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Tel: 0512-55230411 turn 103

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