Why would take the magnetic stainless steel?
People often think that magnets adsorb ss steel materials to verify their quality and authenticity. They are not attractive and non-magnetic. They are considered to be good and genuine; if they are magnetic, they are considered to be counterfeit products. In fact, this is an extremely one-sided and impractical method of identifying errors.
There are many types of stainless steel, which can be divided into several categories according to the organizational structure at room temperature:
1. Austenite type: such as 304, 321, 316, 310, etc.;
2. Martensite or ferrite type: such as 430, 420, 410, etc.;
Austenitic type is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic.
The stainless steel usually used as a decorative tube sheet is mostly austenitic 304 material. Generally speaking, it is non-magnetic or weakly magnetic. However, due to chemical composition fluctuations or different processing conditions caused by smelting, magnetism may also appear, but this cannot be considered as What is the reason for counterfeit or unqualified?
As mentioned above, austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to component segregation or improper heat treatment during smelting, a small amount of martensite or ferrite in austenitic 304 stainless steel will be caused. Body tissue. In this way, 304 stainless steel will have weak magnetic properties.
In addition, after 304 stainless steel is cold-worked, the structure will also be transformed into martensite. The greater the degree of cold-worked deformation, the greater the transformation of martensite and the greater the magnetic properties of the steel. Like a batch of steel belts, Φ76 pipes are produced without obvious magnetic induction, and Φ9.5 pipes are produced. Because the bending deformation is larger, 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 magnetism is more obvious.
In order to completely eliminate the magnetic properties of 304 steel caused by the above-mentioned reasons, the austenite structure can be restored and stabilized by high-temperature solution treatment, thereby eliminating the magnetic properties.
It is particularly important to point out that the magnetism of 304 stainless steel caused by the above reasons is not at the same level as other materials of stainless steel, such as 430 and carbon steel. That is to say, the magnetism of 304 steel always shows weak magnetism.
This tells us that if the stainless steel is weakly magnetic or not magnetic at all, it should be judged as 3-4 or 316; if it is the same as carbon steel, it shows strong magnetism, because it is judged to be not 304.