Magnetic means stainless steel? Not accurate enough! - Shandong Jiugang Tisco Steel Co., Ltd.

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Magnetic means stainless steel? Not accurate enough!

In reality, most people believe 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 and copper alloy can generally imitate the appearance of stainless steel colour, but also no magnetic, easy to be mistaken for stainless steel; and even our current most commonly used 304 stainless steel, after cold processing, there will be different degrees of magnetic. So you can’t just rely on a magnet to determine the authenticity of stainless steel.

 

So where exactly does the magnetism of stainless steel come from?

According to material physics, the magnetism of metals comes from the structure of the electron spin, which is a quantum mechanical property that can either go “up” or “down”.

In ferromagnetic metals, electrons automatically spin in the same direction, while in antiferromagnetic materials, some electrons follow a regular pattern while neighbouring electrons spin in opposite or anti-parallel directions, but for electrons in a triangular lattice, the spin structure no longer exists as both electrons in each triangle must spin in the same direction.

Generally speaking, austenitic stainless steels (represented by 304 stainless steel sheets) are non-magnetic, but may also be weakly magnetic, while ferritic (mainly 430 stainless steel, 409L stainless steel, 439 stainless steel and 445NF etc.) and martensitic (represented by 410 stainless steel) are generally magnetic.

Stainless steel inside some steel (such as 304 stainless steel, etc.) classified as “non-magnetic stainless steel” refers to its magnetic index is lower than a certain value, that is, the general stainless steel are more or less with a certain degree of magnetic.

In addition, the above-mentioned austenite is non-magnetic or weakly magnetic, while ferrite and martensite is magnetic, due to the smelting of the composition of bias or improper heat treatment, will cause austenitic 304 stainless steel in a small amount of martensite or ferrite organization, so 304 stainless steel will appear weakly magnetic.

In addition, 304 stainless steel after cold processing, the tissue structure will also be transformed to martensite, the greater the cold processing deformation, the more martensite transformation, the stronger the magnetic properties will also be.

Want to completely eliminate the magnetic properties of 304 stainless steel, you can restore the stable austenite organization through high temperature solution treatment, so as to eliminate the magnetic properties.

Therefore, the magnetic properties of the material are determined by the regularity of the molecular arrangement and the isotropy of the electron spin, which we consider to be the physical properties of the material, while the corrosion resistance of the material is determined by the chemical composition of the material, which is the chemical properties of the material and has nothing to do with whether the material is magnetic or not.

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