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Magnetism of Stainless Steel

2020-07-20

Austenite is non-magnetic or weak magnetic, while martensite / ferrite is magnetic. Most stainless steel used as decorative plate is Austenitic 304 material. Generally speaking, it is non-magnetic or weakly magnetic. However, due to the fluctuation of chemical composition caused by smelting or different additive state, magnetism may also occur, but this can not be considered as counterfeit or unqualified. What is the reason? As mentioned above, austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to composition segregation or improper heat treatment during smelting or forging, a small amount of martensite or ferrite will be found in Austenitic 304 stainless steel. In this way, 304 stainless steel will have a weak magnetic.

In addition, the microstructure of 304 stainless steel will also transform to martensite after cold working. The greater the cold working deformation, the more martensitic transformation, the greater the magnetic properties of 304 stainless steel. Like the same batch of steel strip, the steel pipe with a diameter of 6cm has no obvious magnetic induction. For the steel pipe with the diameter of 2cm, the magnetic induction is more obvious due to the large cold bending deformation. The deformation of square rectangular pipe is more intense than that of round pipe, especially the corner part, and the magnetic property is more obvious. The same principle, the original non-magnetic 304 stainless steel plate is used in the cold drawing process of making water tank Magnetic production, reflected in the water tank more obvious position is the corner, that is, the largest deformation.

In order to completely eliminate the magnetism of 304 stainless steel plate caused by the above reasons, the stable austenite structure can be restored by high temperature solution treatment (that is, transforming martensite or ferrite into austenite), so as to eliminate magnetism (professional term: degaussing treatment). In particular, it is a normal phenomenon that 304 stainless steel has magnetism due to the above reasons.


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