In daily life, there are many people who know nothing about stainless steel by judging whether it is magnetic or not. Stainless steel is not magnetic, and stainless steel is not stainless steel.
For example, when we go to the supermarket to buy stainless steel items, the salesperson in the supermarket may tell you the same identification method, and even take out a magnet to give you a try.
In fact, this is because of another misunderstanding about the unclear concept of stainless steel. From a metallurgical point of view, "steel" and "iron" are only due to the difference in carbon content, and have nothing to do with magnetism.
In fact, common stainless steels are classified according to the metallographic characteristics, which can be divided into three categories: austenitic stainless steel, martensitic stainless steel and ferritic stainless steel.
Austenitic stainless steel
Austenitic stainless steel is the most widely used stainless steel. It has a chromium content of about 18% and a nickel content of about 8%. It is a chromium-nickel stainless steel and is customarily called 18-8 type stainless steel. Its carbon content is low. Due to the addition of nickel, after solidification treatment, its microstructure is single-phase austenite at room temperature, which is usually non-magnetic.
However, due to smelting chemical composition fluctuations or different processing conditions, magnetism may also occur, such as 304 stainless steel. Due to segregation of components during smelting or improper heat treatment, a small amount of martensite or ferrite structure will appear. In this way, it will be weakly magnetic. In addition, after cold working, 304 stainless steel can precipitate a small amount of martensite structure in the steel. At this time, the steel will have a certain magnetic property, and the greater the cold working deformation, the greater the magnetic properties of the steel.
Martensitic stainless steel
Martensitic stainless steel belongs to chromium stainless steel, and its carbon content is relatively high. After heat treatment, its mechanical properties can be significantly adjusted. Therefore, such steels are generally used after quenching and tempering. At room temperature, the microstructure is tempered martensite, with strong ferromagnetism, such as 1Cr13, 2Cr13, 3Cr13, 4Cr13, 7Cr13 and so on.
Ferritic stainless steel
Ferritic stainless steel also belongs to chromium stainless steel, and its chromium content is generally greater than 11.5%. At room temperature, the microstructure is a single-phase ferrite structure, even if the steel is heated from room temperature to high temperature (900-1100 ℃), its structure will not change significantly. This type of steel also has strong ferromagnetism, representing 430 grades.
From the above analysis, we can see that the method of judging stainless steel material with ferromagnetism is incorrect.
First of all, as the most commonly used austenitic stainless steel, such as 304, it is also possible to be magnetic.
Secondly, even if it is martensitic or ferritic stainless steel, its corrosion resistance may be slightly worse, but considering its price and use environment, as long as it is used properly, it is completely corrosion-resistant and is completely stainless steel.
![Is magnetic stainless steel really stainless steel?]()