People often think that magnets adsorb stainless steel materials to verify their advantages and disadvantages and authenticity, and that they are considered good and genuine without magnetism; If the inhaler has magnetism, it is considered a fake. In fact, this is an extremely one-sided and unrealistic method of identifying errors.

There are various types of stainless steel, which can be divided into several categories according to their organizational structure at room temperature:

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

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

Austenite is nonmagnetic or weakly magnetic, while martensite or ferrite is magnetic.

The stainless steel commonly used for decorative tube sheets is mostly austenitic 304 material, which is generally nonmagnetic or weakly magnetic. However, due to fluctuations in chemical composition or different processing conditions caused by smelting, magnetism may also occur. However, this cannot be considered a counterfeit or unqualified product. What is the reason for this?

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

In addition, after cold processing, the microstructure of 304 stainless steel will also be transformed into martensite. The greater the cold processing deformation, the more martensite transformation, and the greater the magnetic properties of the steel. Like a batch of steel strips, production Φ 76 tubes, no obvious magnetic induction, production Φ 9.5 Tube. Due to the large deformation caused by cold bending, the magnetic induction is more obvious. Due to the larger deformation amount of the production square rectangular tube than the circular tube, especially the angular part, the deformation is more intense and the magnetic induction is more obvious.

To completely eliminate the magnetism of 304 steel caused by the above reasons, the stable austenite structure can be restored through high-temperature solution treatment, thereby eliminating the magnetism.

In particular, due to the above reasons, the magnetism of 304 stainless steel is completely different from that of other materials such as 430 and carbon steel, which means that the magnetism of 304 steel always shows weak magnetism.

This tells us that if stainless steel has weak magnetism or no magnetism at all, it should be judged as 304 or 316 material; If the magnetic properties are the same as those of carbon steel, it shows strong magnetism, and is judged not to be made of 304 material.

Heat treatment cannot explain nonmagnetism

The presence or absence of magnetism in stainless steel cannot be explained from the perspective of heat treatment, as the results are the same regardless of whether heat treatment is performed. The physical quantity of magnetism can only be explained from a physical perspective. According to magnetism, substances in the world can be divided into three types: ferromagnetic substances, paramagnetic substances, and diamagnetic substances.

It is wrong to say that stainless steel is non magnetic. It can only be said that stainless steel is paramagnetic rather than ferromagnetic. "As ferrite, its magnetic transition point is 770 ℃, and the cementite temperature is 230 ℃. In the ferrocarbon phase diagram, the temperature points are called A2 line (point) and A0 line (point), respectively. This temperature point is called the Curie point, which is the physical property of iron and iron and carbon compound cementite. Heat treatment cannot change this physical property. The Curie point is the temperature point at which iron is converted from ferromagnetism to paramagnetism. Since iron above 770 ℃ is converted to gamma iron, which is also known as austenite,", Therefore, austenite is so-called "non magnetic" (actually magnetic, but only paramagnetic), and therefore, all steels with pure austenitic structure are "non magnetic". Therefore, only austenitic stainless steel among stainless steels is "non magnetic", such as wear-resistant steel ZGMn13. Although it is not stainless steel, it is also "non magnetic" due to its austenitic structure at room temperature.