Why Is The 304 Stainless Steel Plate Magnetic?

People often use magnets to attract stainless steel plates to verify their pros and cons and their authenticity. If they do not attract and have no magnetism, they think they are good and genuine; those who attract magnets are considered counterfeit. In fact, this is an extremely one-sided, unrealistic and wrong identification method.

There are many kinds of stainless steel plates, which can be divided into several categories according to the 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.;

The austenitic type is non-magnetic or weakly magnetic, and the martensite or ferrite is magnetic.

Most of the stainless steel plates usually used as decorative tube sheets are austenitic 304 materials. Generally speaking, they are non-magnetic or weakly magnetic, but they may also appear magnetic due to fluctuations in chemical composition or different processing conditions caused by smelting, but this cannot be considered Is it fake or substandard, 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 in austenitic 304 stainless steel will be caused. Body tissue. In this way, the 304 stainless steel plate will have weak magnetism.

In addition, after cold working of 304 stainless steel, the microstructure will also be transformed to martensite. The greater the cold working deformation, the more martensite transformation, and the greater the magnetic properties of the steel. Like a batch of steel strips, Φ76 tubes are produced without obvious magnetic induction, and Φ9.5 tubes are produced. The magnetic induction is more obvious due to the large deformation of the bending and bending. 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 magnetic force is more obvious.

In order to completely eliminate the magnetic properties of 304 steel caused by the above reasons, the stable austenite structure can be restored by high-temperature solution treatment, thereby eliminating the magnetic properties.

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

This tells us that if the stainless steel plate is weakly magnetic or not magnetic at all, it should be judged as 304 or 316 material; if it is the same as carbon steel, it shows strong magnetism, because it is judged as not 304 material.