Why are stainless steel screws magnetic?(1)

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People often think that magnets absorb stainless steel to verify its merits and authenticity. It does not attract non-magnetic materials. It is considered good and genuine. The attractor is magnetic and it is considered fake. In fact, this is a very one-sided, impractical and wrong method of identification.
There are many types of stainless steel, which can be divided into several categories according to organizational structure at room temperature:
1. Austenitic type: such as 304, 321, 316, 310, etc .;
2. Martensite or ferrite type: such as 430, 420, 410, etc .;
The austenite type is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic.
The most commonly used stainless steel for decorative tube sheets is austenitic 304 material, which is generally non-magnetic or weak-magnetic, but the magnetic composition may fluctuate due to smelting or the processing state may be different, but this may not be considered as Counterfeit or unqualified, what is the reason?
As mentioned above, austenite is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic. Due to segregation of components during smelting or improper heat treatment, it will cause a small amount of martensite or ferrite in austenitic 304 stainless steel. Body organization. In this way, 304 stainless steel will have a weak magnetic.
In addition, after cold working of 304 stainless steel, the structure will also be transformed into martensite. The greater the degree of cold working deformation, the more the martensite transformation, the greater the magnetic properties of the steel. Like a batch of steel strips, Φ76 tubes are produced, without obvious magnetic induction, Φ9.5 tubes are produced. Due to the large bending deformation, the magnetic induction is more obvious. 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 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 to eliminate the magnetic properties.

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