Most people think that stainless steel is not magnetic, and with the help of magnets to identify stainless steel, this method is very unscientific.
First of all, zinc alloy, copper alloy can generally imitate the appearance of stainless steel color, there is no magnetism, easy to mistake for stainless steel; and even if we are currently the most commonly used 304 steel, after cold processing, there will be varying degrees of magnetism.
In fact, all austenitic stainless steel, only in a vacuum state can be completely non-magnetic. The permeability of a material in a magnetic field is measured relative to the permeability µ of the material in a vacuum. If µ is close to 1.0, the material has a low permeability. Therefore, you cannot judge the authenticity of stainless steel by a magnet alone.
Causes of magnetism in austenitic steels:
Stainless steel inside some steel (such as 304, etc.) classified as “non-magnetic stainless steel” refers to its magnetic index is lower than a certain value, that is to say, the general stainless steel are more or less with a certain degree of magnetism.
As a result of smelting composition segregation or improper heat treatment, will cause austenitic 304 stainless steel in a small amount of martensite or ferrite organization, so that 304 stainless steel will appear in the weak magnetic.
Characteristics of the magnetization ability of various materials, also suitable for stainless steel, austenitic stainless steel itself for the presentation of face-centered cubic crystal structure, the surface of the organization is paramagnetic, so the austenitic organization itself does not show magnetic.
After cold deformation is induced part of the austenite into martensite and ferrite organization of the external conditions, the general deformation of martensite with the increase in cold deformation and deformation temperature and increase, that is to say, the greater the cold deformation, the more martensite transformation, the stronger the magnetism will be.
Process measures to reduce permeability:
Because some customers have strict requirements on the magnetic permeability of austenitic stainless steel products, and according to the national standard procurement is due to the differences in chemical composition will lead to different magnetic permeability of each batch of material, while in the product production, processing, transit, welding process will also cause changes in the magnetic permeability, to meet the requirements of the product use.
Through the commonly used austenitic stainless steel material structure and organization analysis, from the microscopic principle, organization, chemical composition of the magnetic permeability of the impact of various aspects of the analysis, in which the chemical composition of the magnetic permeability of the greatest impact, so through the adjustment of the chemical composition, so that the material to obtain a stable austenitic organization and the use of stable and effective process measures is to ensure that the magnetic permeability of the product is the key to qualified.
