Why Is 304 Stainless Steel Also Magnetic?

Some people often think that a magnet is used to test the quality of stainless steel. The magnet does not attract and is not magnetic, and it is genuine; if it is magnetic, it is considered a fake. In fact, this is an extremely one-sided, unrealistic and wrong identification method.

Generally speaking, stainless steel is either magnetic or non-magnetic, austenitic is non-magnetic or weakly magnetic, such as 201, 202, 304, 316, etc.; martensite or ferrite is magnetic, such as 430, 420, 410, etc.

However, due to the segregation of components or improper heat treatment during smelting, a small amount of martensite or ferrite will be present in austenitic 304 stainless steel. 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 to martensite. The greater the cold working deformation, the more martensite transformation, and the greater the magnetic properties. Just like a batch of stainless steel wire, it is made into a straight branch without obvious magnetic induction, but when it is bent into a rectangle or a circle, some magnetism is generated due to the large cold bending deformation, especially the corners have more obvious magnetism.

In order to complete the elimination of the magnetic properties of the above 304 stainless steel, the stable austenite structure can be restored by high temperature treatment, thereby eliminating the magnetic properties.

In particular, it should be reminded that the magnetic properties of 304 stainless steel caused by the above reasons are completely different from the magnetic properties of other materials such as 430 and carbon steel, which means that the magnetic properties of 304 stainless steel are always weakly magnetic.