People often think that magnets attract alloy steel pipes to verify their quality and authenticity. If they do not attract magnets, they think they are good and genuine; if they attract magnets, they think they are fake. This is an extremely one-sided, unrealistic, and wrong method of identification. There are many types of alloy tubes, 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. Martensite or ferrite type: such as 430, 420, 410, etc.;

Austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Most alloy tubes commonly used as decorative tube sheets are made of austenitic 304 material. Generally speaking, they are non-magnetic or weakly magnetic. However, magnetism may also occur due to fluctuations in chemical composition caused by smelting or different processing conditions, but this cannot be considered Is it 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 or improper heat treatment during smelting, a small amount of martensite or iron will be caused in the austenitic 304 alloy tube. body tissue. In this way, the 304 alloy tube will have weak magnetism. In addition, after the cold working of 304 alloy steel pipe, the organizational structure will also transform into martensite. The greater the degree of cold working deformation, the more martensitic transformation, and the greater the magnetism of the steel. Just like a batch number of steel strips, Φ76 pipes are produced. There is no obvious magnetic induction, and Φ9.5 pipes are produced. Because the bending deformation is larger, the magnetic induction will be more obvious. The deformation of the square rectangular tube is larger than that of the round tube, especially the corner part, the deformation is more intense and the magnetism is more obvious.

To 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. It should be pointed out in particular that the magnetism of 304 alloy tubes caused by the above reasons is not at the same level as the magnetism of alloy tubes of other materials, such as 430 and carbon steel. In other words, the magnetism of 304 steel always shows weak magnetism.

This tells us that if the alloy steel pipe has weak magnetism or no magnetism at all, it should be identified as 304 or 316 material; if it has the same magnetism as carbon steel and shows strong magnetism, it should be identified as not 304 material.