There are many kind of Stainless steel , from the temperature according to the organizational structure can be divided into several categories:
1, austenitic body type: such as 304, 321, 316, 310,
2, martensite or ferrite body type: such as 430, 420, 410, etc.
Austenite is non-magnetic or weakly magnetic, martensite or ferrite is magnetic. Usually used as decorative pipe Board stainless steel is mostly austenitic body 304 material, generally magnetic or weak magnetic, but due to smelting caused by chemical composition fluctuations or different processing State may also appear magnetic, but this can not be considered fake or unqualified, what is the reason?
It is mentioned above that austenite is non-magnetic or weak magnetic, and martensite or ferrite is magnetic, due to smelting component segregation or improper heat treatment, will cause austenitic 304 stainless Steel in a small number of martensite or ferrite tissue. In this way, 304 stainless steel will have a weak magnetism.
In addition, 304 stainless steel after cold processing, the tissue structure will also be converted to martensite, the greater the deformation of cold processing, the more martensite conversion, the greater the magnetism of steel. Like a batch of steel strip, the production of φ76 tube, no obvious magnetic sense, the production of φ9.5 tube. Because of the large magnetic sense of the corner deformation is obvious, the production square rectangular tube because the deformation is larger than the circular tube, especially the folding part, deformation more intense magnetism is more obvious. In order to completely eliminate the magnetic properties of 304 steel caused by the above reasons, the stable austenitic tissue can be restored by high temperature solidification treatment, thus eliminating magnetism.
In particular, due to the above reasons caused by the 304 stainless steel magnetism, and other materials of stainless steel, such as 430, carbon steel magnetism is not the same level at all, that is, 304 steel magnetism always shows weak magnetism. This tells us that if stainless steel is weakly magnetic or completely non-magnetic, it should be judged as 304 or 316 material, and if it is the same as the magnetism of carbon steel, it shows strong magnetism because it is not a 304 material.