Stainless steel with magnetic reasons
People often think that magnets adsorb stainless steel to verify its pros and cons and authenticity. If it is not sucked, it will be non-magnetic. It is considered to be good and genuine. If it is magnetic, it is considered to be counterfeit and fake. In fact, this is an extremely one-sided, wrong way of distinguishing.
There are many types of stainless steel, which can be divided into the following categories according to the 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.
Most of the stainless steels used as decorative tube sheets are austenitic type 304 materials, which are generally non-magnetic or weakly magnetic. However, magnetic properties may occur due to fluctuations in chemical composition or processing conditions due to smelting, but this cannot be considered as Counterfeit or unqualified, what is the reason?
It is mentioned above that austenite is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic. Due to segregation or improper heat treatment during smelting, a small amount of martensite or ferrite in austenitic 304 stainless steel is caused. Body organization. Thus, 304 stainless steel will have weak magnetic properties.
In addition, 304 stainless steel is cold-worked, and the microstructure is also transformed into martensite. The greater the cold work deformation, the more martensite transformation and the greater the magnetic properties of the steel. Like a batch of steel strips, the production of Φ76 tube, no obvious magnetic sense; the production of Φ9.5 tube, due to the large deformation of the bending deformation of the magnetic sense is obvious; the production of square rectangular tube due to the deformation is larger than the round tube, especially the angled part The deformation is more intense and the magnetic is more obvious.
In order to completely eliminate the magnetic properties of the 304 steel caused by the above reasons, the austenite structure can be restored by high-temperature solution treatment to eliminate the magnetic properties.
In particular, the magnetic properties of 304 stainless steel caused by the above reasons are not at the same level as the magnetic properties of other materials such as 430 and carbon steel. That is to say, the magnetic properties of 304 steel always show weak magnetic properties.
This tells us that if the stainless steel strip is weakly magnetic or not magnetic at all, it should be judged to be 304 or 316. If it is magnetic similar to carbon steel and shows strong magnetism, it should be judged as not 304 material.
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