The reason stainless steel is magnetic is because most stainless steel contains martensite,austenite, or iron.Martensite or iron will show magnetism, so some stainless steel will be magnetic.And Austenite does not show magnetism, which is why some stainless steel shows magnetism, and some have no magnetism.
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The variety of stainless steel is divided into austenitic type, martensite or iron body type.
Austenitic type: 304,321,316,310; martensite or ferrite type: 430,420,410;
Austenitic type 304 material is generally used as a decorative stainless steel pipe, showing no magnetic or weak magnetic.However, improper segregation or heat treatment during smelting will cause a small amount of martensite or iron in austenitic 304 stainless steel, making 304 stainless steel weak magnetic.If the 304 stainless steel through cold processing, the tissue structure will also convert to martensite, the greater the deformation of cold processing, the more martensite conversion, the greater the magnetism of the steel.
People often think that magnet adsorption stainless steel, verify its merits and authenticity, not suction without magnetic, think is good, genuine; suction magnetic, is considered fake.In fact, this is an extremely one-sided, unrealistic and wrong method of discrimination.
There are many kinds of stainless steel, which can be divided into several categories according to the tissue structure at room temperature:
1. Austenitic type: such as 304,321,316,310, etc.
2. Martensite or ferrite type: such as 430,420,410, etc.
The stainless steel usually used as decorative pipe plate is austenitic 304 material, generally speaking is no magnetic or weak magnetic, but because of smelting caused by chemical composition fluctuations or processing state may also appear magnetism, but this can not be considered fake or unqualified, what reason is this?
Above mentioned austenite is not magnetic or weak magnetic, and martensite or ferrite is magnetic, because of smelting composition segregation or improper heat treatment, will result in a small amount of austenite or ferrite tissue in austenite 304 stainless steel.This creates weak magnetic properties in the 304 stainless steel.
In addition, 304 stainless steel after cold processing, the tissue structure will also be transformed into martensite, the greater the cold processing deformation, the more martensite conversion, the greater the magnetic steel.Like a batch of steel, the production of kitchen utensils with less distortion such as (flat shovel, knife, etc.), will have no obvious magnetic sense; but the production of large distortion deformation of kitchen utensils such as (bucket, spoon, spatula, etc.), because of the deformation of large magnetic sense is obvious.Production of rectangular products are larger than the circle, especially in the folding corner part , the deformation is more intense and magnetic obvious.
In order to completely eliminate the magnetism of 304 steel caused by the above reasons, the stable austenitic tissue can be restored by high temperature solid solution treatment, thus eliminating the magnetism.
In particular, it is proposed that the magnetism of 304 stainless steel caused by the above reasons is not in the same level as other 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 stainless steel is weak or not magnetic at all, 304 or 430, if as magnetic as carbon steel, not 304.