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Stainless steel plate, stainless steel coil why also rust?

Stainless steel plate, stainless steel coil why also rust?

Time:2022-04-02 Source:Wuxi Jianuo Special Steel Co., Ltd.

When the appearance of stainless steel pipe brown rust spots (points), people are surprised: think “stainless steel is not rust, rust is not stainless steel, may be a problem with the quality of steel”. In fact, this is a one-sided misconception of the lack of understanding of stainless steel. Stainless steel will rust under certain conditions

Stainless steel has the ability to resist atmospheric oxidation — that is, stainless steel, but also in the medium containing acid, alkali, salt is the ability to corrode — that is, corrosion resistance. But the size of its corrosion resistance is with its own chemical composition of steel, plus mutual state, application conditions and environmental media type and change. Such as 304 steel pipe, in a dry and clean atmosphere, there is absolutely excellent corrosion resistance, but it will be moved to the seaside region, in the sea spray 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 be resistant to corrosion, not rust.

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The outer surface film is destroyed in many ways, the most common in daily life are the following.

Stainless steel is by its appearance of a layer of very thin and consolidation of fine and stable chromium-rich oxide film (protective film), to avoid the continued penetration of oxygen atoms, continued oxidation, and the ability to obtain corrosion resistance. Once there is some reason, this film is destroyed from time to time, the oxygen atoms in the air or liquid will infiltrate from time to time or the iron atoms in the metal will precipitate out from time to time, forming loose iron oxide, and the metal appearance will be rusted from time to time. The appearance of the film is destroyed in many ways, the following are common in daily life.

1, the stainless steel surface containing other metal elements of dust or adhesion of metal particles, in the humid air, adhesion and stainless steel condensation, the two will be connected into a microcell, triggering an electrochemical reaction, the maintenance film was destroyed, known as electrochemical corrosion.

2, stainless steel exterior adhesion of organic juices (such as squash, noodle soup, spit, etc.), in the presence of water and oxygen conditions, constituting an organic acid, a long time then the organic acid corrosion of the metal exterior.

3, stainless steel exterior adhesion containing acid, alkali, salt substances (such as decorative walls of alkaline water, lime water spray), provoking partial corrosion.

4, in the polluted air (such as containing a large number of sulfides, carbon dioxide, nitrogen oxide atmosphere), encountering condensate, sulfuric acid, nitric acid, acetic acid liquid point, causing chemical corrosion.

To ensure that the metal appearance of eternal brightness, not rusted, we advocate.

All of the above conditions can form the stainless steel exterior protective film destruction triggered by rust and corrosion. Therefore, in order to ensure that the metal appearance of eternal brightness, not be rusted, we advocate.

 

1. must often stop cleaning and scrubbing the decorative stainless steel exterior to remove the adhesions and eliminate the external elements that trigger the trim.

2, the seaside region to use 316 stainless steel, 316 material can resist seawater corrosion.

3, some stainless steel pipe chemical composition on the market can not meet the corresponding national norms, not up to 304 material requirements. Therefore, it will also cause rust, which requires users to carefully select the products of reputable manufacturers.

 

Why is stainless steel also magnetic?

 

People often think that the magnet adsorbs the stainless steel material, test its merits and authenticity, not suck no magnetic, thought to be good, the name is true; suckers have magnetic, it is thought to be counterfeit. In fact, this is an extremely one-sided, not really the wrong way to distinguish.

 

The variety of stainless steel, at room temperature, according to the tissue structure can be divided into several categories.

1, austenitic type: such as 201, 202, 301, 304, 316, etc..

2, martensitic or ferritic type: such as 430, 420, 410, etc..

 

Austenitic type is non-magnetic or weakly magnetic, martensitic or ferritic is magnetic.

Most of the stainless steel usually used as decorative pipe plate is austenitic type 304 material, generally speaking, is non-magnetic or weakly magnetic, but due to the formation of smelting chemical composition fluctuations or processing state may also present magnetic, but this can not be thought of as impostor or unqualified, what is the reason for this?

Above mentioned austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic, due to smelting composition bias or improper thermal treatment, will form a small amount of austenitic 304 stainless steel in martensite or ferrite organization. In this way, 304 stainless steel with a small amount of magnetic properties.

In addition, 304 stainless steel after cold processing, the tissue structure will also be transformed to martensite, the greater the degree of cold processing deformation, the more martensite transformation, the greater the magnetic properties of steel. As if a batch of number of steel strip, consumption Φ76 tube, no obvious magnetic sense, consumption Φ9.5 tube. Because of the larger deformation of cold bending, the magnetic sense is obvious, and because of the larger deformation of square and rectangular pipes, especially the corner of the folding part, the deformation is more intense and the magnetic sense is more obvious.

To completely eliminate the above causes the formation of 304 steel magnetism, can be after high-temperature solution treatment to restore stable austenite organization, thus eliminating the magnetic.

In particular, the above causes the formation of 304 stainless steel magnetism, and other materials of stainless steel, such as 430, carbon steel magnetism is not the same level, that is, the magnetic properties of 304 steel has been weak magnetism.

This informs us that if the stainless steel with weak magnetism or complete non-magnetic, should be judged as 304 or 316 material; if the same as the carbon steel magnetism, showing strong magnetic, because the judgment is not 304 material.