Magnetic Properties of Stainless Steel

People often use magnets to adsorb stainless steel to verify its pros and cons and its authenticity. If it does not attract and has no magnetism, it is considered to be good and genuine. If the attractor has magnetism, it is considered to be counterfeit. In fact, this is an extremely one-sided, unrealistic and wrong identification method.


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

1. Austenitic type: such as 201, 202, 301, 304, 316, 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 usually used for decorative tube sheets is austenitic 304 material, which is generally non-magnetic or weakly magnetic, but may also appear magnetic due to fluctuations in chemical composition or different processing conditions caused by smelting, but this cannot be considered as a Counterfeit or substandard, 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 or ferrite in austenitic 304 stainless steel will be caused. body tissue. In this way, 304 stainless steel will have weak magnetism.


In addition, after cold working of 304 stainless steel, the structure will also be transformed into 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 caused by the above reasons is completely different from the magnetism 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 the stainless steel strip is weakly magnetic or completely non-magnetic, it should be judged as 304 or 316 material. If it is the same as carbon steel and shows strong magnetism, it should be judged as not 304 material.