Why is stainless steel also magnetic?

People often think that magnets attract stainless steel to verify its advantages and authenticity, and that magnets that do not attract stainless steel are considered good and truly valuable; in fact, this is an extremely one-sided and unrealistic way of misidentification.

Stainless steel has a variety of organizational structures at room temperature. According to the organizational structure, it can be divided into the following categories:

Austenitic stainless steel: such as 304, 321, 316, 310, etc. ;Martensite or ferrite type: such as 430, 420, 410, etc.;

Austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Most stainless steel commonly used as decorative tube sheets are austenitic 304 type materials, which are generally non-magnetic or weakly magnetic. However, magnetism may also appear due to fluctuations in chemical composition caused by smelting or different processing states, but this cannot be considered counterfeit. Or unqualified, what is the reason?

The above-mentioned austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to component decomposition or heat treatment smelting, a small amount of martensite or ferrite structure will be produced 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 organizational structure will also transform to martensite. The greater the cold working deformation, the more martensitic transformation, and the greater the magnetism of the magnetic steel. Like a batch of steel strips, the 76 tubes produced have no obvious magnetic induction, and the 9.5 tubes produced.

Due to the large magnetic deformation, the deformation of the rectangular tube produced is greater than that of the circular tube, especially at the corners, and the stronger the magnetic deformation is, the more obvious it is. In order to completely eliminate the magnetism of 304 steel due to the above reasons, the stable Australasian structure can be restored through high-temperature solution treatment, thereby eliminating the magnetism.

In particular, the magnetism of 304 stainless steel due to the above reasons is different from the magnetism level of other stainless steel materials such as 430 and carbon steel, that is, the magnetism of 304 steel always shows weak magnetism.