There are many kinds of stainless steel, which are divided into austenitic type, martensitic type or iron element type according to structure. Austenite type: 304,321,316,310; Martensite or ferrite type: 430, 420, 410; Austenite type 304 material is generally used as decorative stainless steel pipe, showing no magnetism or weak magnetism. However, the composition segregation or improper heat treatment during smelting will produce a small amount of martensite or iron in austenitic 304 stainless steel, which will make 304 stainless steel have weak magnetism. If 304 stainless steel is cold-worked, its structure will also be transformed into martensite. The greater the cold deformation, the more martensite transformation and the stronger the magnetic properties of steel.