June 5, 2015 Lelang sanitary ware

Lelelang sanitary ware

Many customers are surprised that stainless steel products are rusty! Many manufacturers don't know how to explain! Next, Lelang Xiaobian will give you science!

Why is stainless steel rusty?

When brown rust spots (spots) appeared on the surface of stainless steel pipes, people were surprised: they thought that "stainless steel is not rusty, rusty is not stainless steel, and there may be a problem with the steel quality". In fact, this is a one-sided wrong view 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, rust resistance. At the same time, it also has the ability to corrode in the medium containing acid, alkali and salt, that is, corrosion resistance. However, the corrosion resistance of the steel varies with its chemical composition, interaction state, service condition and environmental medium type. For example, 304 steel pipe has absolutely excellent corrosion resistance in a dry and clean atmosphere, but if it is moved to the coastal area, it will soon rust in the sea fog containing a lot of salt; While 316 steel pipe performs well. Therefore, not any kind of stainless steel can resist corrosion and rust in any environment.

Stainless steel is a thin, firm, fine and stable chromium rich oxide film (protective film) formed on its surface to prevent the continuous infiltration and oxidation of oxygen atoms and obtain the ability to resist corrosion. Once the film is continuously damaged for some reason, the oxygen atoms in the air or liquid will continuously penetrate or the iron atoms in the metal will continuously separate out, forming loose iron oxide, and the metal surface will be continuously corroded. This surface facial mask is damaged in many ways, and the following are common in daily life:

1. there are dust containing other metal elements or attachments of dissimilar metal particles on the surface of stainless steel. In the humid air, the condensate between the attachments and stainless steel will connect them into a micro battery, causing electrochemical reaction and damaging the protective film, which is called electrochemical corrosion.

2. the stainless steel surface is adhered with organic juice (such as melons and vegetables, noodle soup, phlegm, etc.), which constitutes organic acid in the presence of water and oxygen. For a long time, the organic acid will corrode the metal surface.

3. the stainless steel surface contains acid, alkali and salt substances (such as alkali water and lime water splashing on the decoration wall), causing local corrosion.

4. in polluted air (such as atmosphere containing a large amount of sulfide, carbon oxide and nitrogen oxide), sulfuric acid, nitric acid and acetic acid liquid points are formed in the presence of condensate, causing chemical corrosion.

The above conditions can cause the damage of the protective film on the surface of stainless steel and lead to corrosion. Therefore, in order to ensure that the metal surface is permanently bright and not corroded, we suggest:

1. the decorative stainless steel surface must be cleaned and scrubbed frequently to remove attachments and external factors causing corrosion.

2. 316 stainless steel shall be used in coastal areas, which can resist seawater corrosion.

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

People often use magnets to adsorb stainless steel materials to verify their advantages and disadvantages and authenticity. If they are not magnetic, they think they are good and genuine; If the attractor is magnetic, it is considered to be a fake. In fact, this is an extremely one-sided, impractical and wrong identification method.

There are many kinds of stainless steel, which can be divided into several types according to the organizational structure at room temperature:

1. austenite type: such as 304, 321, 316, 310, etc;

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

Austenite type is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic.

Most stainless steel used as decorative tube sheet is Austenitic 304 material. Generally speaking, it is non-magnetic or weak magnetic. However, magnetism may also occur due to chemical composition fluctuation caused by smelting or different processing conditions. However, this cannot be considered as counterfeit or unqualified. What is the reason?

As mentioned above, austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to component segregation during smelting or improper heat treatment, a small amount of martensite or ferrite in Austenitic 304 stainless steel will be caused. In this way, 304 stainless steel will have weak magnetism.

In addition, after cold working, the microstructure of 304 stainless steel will also transform to martensite. The greater the cold working deformation, the more martensite transformation, and the greater the magnetic properties of the steel. Production of steel strips of the same batch number Φ 76 tube, no obvious magnetic induction, production Φ 9.5 pipe. The magnetic induction is more obvious due to the large bending deformation. The deformation of square rectangular tubes is larger than that of round tubes, especially in the angle part. The deformation is more intense and the magnetism is more obvious.

In order to completely eliminate the magnetism of 304 steel caused by the above reasons, the stable austenite structure can be recovered through high-temperature solid solution treatment, so as to eliminate the magnetism.

In particular, the magnetism of 304 stainless steel caused by the above reasons is not at the same level as that of other stainless steels, such as 430 and carbon steel, that is to say, the magnetism of 304 steel always shows weak magnetism.

This tells us that if stainless steel is weakly magnetic or completely non-magnetic, it should be judged as 304 or 316 material; If it is the same as the magnetic properties of carbon steel, it shows strong magnetic properties, because it is judged that it is not made of 304 material.

We suggest that stainless steel products should be purchased from reputable manufacturers. Don't be greedy and beware of being cheated.

(if there is any infringement, please inform us to delete it in time. Thank you!)