There are many kinds of stainless steel pipe fittings, which can be divided into several categories according to the organizational structure at room temperature:
1. Austenitic type: such as 201, 202, 301, 304, 316, etc.; 2. Martensitic or ferritic type: such as 430, 420, 410, etc.;
Austenite is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic.
Most of the stainless steel pipe fittings used as decorative tube sheets are made of austenitic 304 material. Generally speaking, they are non-magnetic or weakly magnetic. However, magnetic properties may also appear due to chemical composition fluctuations or different processing conditions caused by smelting, but this cannot be regarded as Is it counterfeit or unqualified, what is the reason?
It is mentioned above that austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to composition segregation or improper heat treatment during smelting, a small amount of martensite or iron in austenitic 304 stainless steel pipe fittings will be caused. Body tissue. In this way, there will be weak magnetism in 304 stainless steel pipe fittings.
In addition, after cold working, the structure of 304 stainless steel pipe fittings will also transform into martensite. The greater the degree of cold working deformation, the more martensite transformation, and the greater the magnetic properties of the steel. Like a batch of steel strips, Φ76 tubes are produced, without obvious magnetic induction, and Φ9.5 tubes are produced. The magnetic induction is more obvious due to the larger cold bending deformation. The deformation of square and rectangular pipes is larger than that of round pipes, especially at the corners, and the deformation is more intense and the magnetism is more obvious.
In order to completely eliminate the magnetism of 304 steel caused by the above reasons, the stable austenite structure can be recovered by high temperature solution treatment, so as to eliminate the magnetism. In particular, the magnetism of 304 stainless steel pipe fittings caused by the above reasons is not at the same level as that of stainless steel pipe fittings made of other materials, 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 pipe fitting has weak magnetism or no magnetism at all, it should be identified as 304 or 316 material; if it is the same as carbon steel, it shows strong magnetism, because it is not 304 material.