Ordinary steel is carbon steel, that is, iron-carbon alloy. According to the level of carbon content, it is divided into low carbon steel (to be called wrought iron), medium carbon steel and cast iron. Generally less than 0.2% carbon content is called low carbon steel, commonly known as wrought iron or pure iron; The content of 0.2-1.7% is called steel; The content above 1.7% is called pig iron.

Steel containing more than 12.5% chromium in steel, with a high resistance to external media (acid, alkali salt) corrosion of steel, called stainless steel. According to the structure of the steel, stainless steel can be divided into martensitic, ferritic, austenitic, ferritic-austenitic, precipitation-hardened stainless steel, according to the national standard GB3280-92, a total of 55 provisions.

In daily life, we are exposed to more Austenitic stainless steel (some people call it nickel stainless steel) and Martensitic stainless steel (some people call it "stainless iron", but it is not scientific and easy to misunderstand. Typical grades of Austenitic stainless steel are 0Cr18Ni9, that is, "304" and 1Cr18Ni9Ti. Martensitic stainless steel, such as stainless steel for manufacturing knives and scissors, is mainly 2Cr13, 3Cr13, 6Cr13, 7Cr17 and so on.

Due to the difference in the composition of the two types of stainless steel, the metal microstructure inside is also different. Austenitic stainless steel due to the addition of higher chromium and nickel in the steel (containing chromium in about 18%, Ni in more than 4%), the internal organization of the steel presents a called austenite organizational state, this organization is not magnetic conductivity, can not be attracted by magnets. Commonly used as decorative materials, such as stainless steel pipes, towel racks, tableware, stoves, etc.

Martensitic stainless steel should be used for the production of knife and scissors. Because the knife scissors have the function of cutting items, there must be sharpness, and there must be a certain hardness. This kind of stainless steel must be heat treated to make its internal structure change and increase the hardness before it can be cut. However, the internal structure of this kind of stainless steel is tempered martensite, which has magnetic conductivity and can be attracted by magnets. Therefore, it is not simple to use whether it is magnetic to explain whether it is stainless steel material.