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Why Are Stainless Steel Plates Magnetic?

Jan. 14, 2020

People often use magnets to attract stainless steel plates to verify their strengths, weaknesses, and authenticity. They do not attract non-magnetic materials, which are considered good and genuine. For those who are magnetic, they are considered counterfeit. In fact, this is an extremely one-sided and impractical method of identifying errors.

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

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

2. Martensite or ferrite type: such as 430, 420, 410, etc.

Austenite type is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Most of the stainless steel plates commonly used as decorative tube plates are austenitic 304 materials, which are generally non-magnetic or weakly magnetic, but they may also be magnetic due to fluctuations in chemical composition or different processing conditions caused by smelting, but this cannot be considered Is it counterfeit or unqualified? What is the reason for this?

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 in the austenitic 304 Stainless Steel Plate or Ferrite structure. In this way, 304 stainless steel plate will have a weak magnetism.

304 Stainless Steel Plate

304 Stainless Steel Plate

In addition, the structure of 304 stainless steel plate will be transformed to martensite after cold working. The greater the degree of deformation during cold working, 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. Due to the large bending deformation, the magnetic induction is obvious. Due to the larger amount of deformation in the production of rectangular tubes than round tubes, especially the corners, the deformation is more intense and the magnetic is more obvious.

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

In particular, the magnetic properties of the 304 stainless steel plate due to the above reasons are completely different from the magnetic properties of stainless steel plates of other materials, such as 430 and carbon steel, which means that the magnetic properties of 304 steel always show weak magnetism. 

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

The above is the reason why the stainless steel sheet introduced by 316l Stainless Steel Sheet Manufacturer will be magnetic. Hope to help you.

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