Stainless steel has the characteristics of stainless steel, acid resistance, high temperature resistance, wear resistance and austenite is generally nonmagnetic. Stainless steel is a common high-grade alloy steel, such as stainless steel knives, stainless steel kitchen utensils and stainless steel building materials in our daily life. Most of the stainless steels we see every day are nickel-chromium stainless steels with basically the same grade as 20 1 and 304, and chromium stainless steels with the grade of 1-4 Cr 13 (common people call them "stainless iron"). In China, there are more than 100 kinds of stainless steel (steel grade), and the properties and values of stainless steel are quite different because of the different elements and contents in the steel grade. Therefore, the identification of stainless steel must be carefully studied, the mark of steel grade must be made clear, and it can be correctly identified by comprehensive tests and other methods. At present, we mainly have the following methods to identify stainless steel: the whole stainless steel, the source of which is generally ordered by steel mills or imported from abroad, and the overstocked and overstocked processed goods in society. Different sources of stainless steel have different identification methods. Generally, it is only necessary to check the marks on the steel or packaging according to the quality certificate of the imported or steel mill to identify the stainless steel ordered by the imported or steel mill.