In real life, most people think that stainless steel is non-magnetic and use magnets to identify stainless steel. This method is very unscientific. People often think that magnets absorb stainless steel to verify its quality and authenticity. If it does not absorb magnetism, it is considered to be good and genuine; if it absorbs magnetism, it is considered to be a fake. This is an extremely one-sided, impractical, and wrong identification method. There are many types of stainless steel, which can be divided into several categories according to the organizational structure at room temperature.
1. Austenite type such as 304, 321, 316, 310, etc.;
2. Martensite or ferrite type such as 430, 420, 410, etc.; Austenite type is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic. Most of the stainless steel used for decorative tube sheets is austenitic 304 material, which is generally non-magnetic or weakly magnetic. However, due to fluctuations in chemical composition or different processing conditions caused by smelting, magnetism may also occur, but this cannot be considered 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 ferrite organization will be caused in austenitic 304 stainless steel. In this way, 304 stainless steel will have weak magnetism. In addition, after cold working, the organizational structure of 304 stainless steel will also transform into martensite. The greater the cold working deformation, the more martensite transformation, and the greater the magnetism of the steel. For the same batch of steel strips, there is no obvious magnetic induction when producing Φ76 tubes, and Φ9.5 tubes are produced. The magnetic induction is more obvious due to the large cold bending deformation. The deformation of square and rectangular tubes is larger than that of round tubes, especially the corners, and the deformation is more intense and the magnetism is more obvious. To eliminate the magnetism of 304 steel caused by the above reasons, high-temperature solid solution treatment can be used to restore the stable austenite structure, thereby eliminating the magnetism. It should be particularly pointed out that the magnetism of 304 stainless steel caused by the above reasons is completely different from the magnetism of other stainless steels, such as 430 and carbon steel, that is, 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 it shows strong magnetism like carbon steel, it should be judged as not 304 material. 304 and 316 are both austenitic stainless steels, which are single-phase. They have weak magnetism.
Post time: Jan-16-2025