Some questions about magnetism in SUS 304
Austenitic the stainless steel is non-magnetic or weakly magnetic, while austenite-ferrite duplex stainless steel is magnetic. 304 stainless steel sheet is an austenitic stainless steel, but why does it contain a small amount of martensite or ferrite structure?
The main purpose of demagnetization is to reduce or completely eliminate the magnetization of a stainless steel material by changing the magnetic properties of the material. This can be accomplished in a number of ways. One common method is the use of an AC magnetic field. By subjecting a stainless steel material to an AC magnetic field and gradually reducing the strength of the field, the material's magnetic properties can be gradually eliminated. This process needs to be carried out under specific temperature and time conditions to ensure the effectiveness of the demagnetization.
During smelting or forging, composition segregation or improper heat treatment can cause 304 stainless steel sheet to contain a small amount of martensite or ferrite structure. As a result, the 304 stainless steel sheet will have a weak magnetism. Moreover, after cold working, the microstructure of the 304 stainless steel sheet will also transform towards martensitic stainless steel. The greater the degree of deformation in cold working, the more martensite transformation occurs, and the greater the magnetism of the 304 stainless steel sheet.
For example, an originally non-magnetic 304 stainless steel sheet may acquire magnetism during the cold stretching process for making sink basins, and the most obvious position for magnetism in the sink basin is at the corner, which is the area with the greatest deformation. To completely eliminate the magnetism of the 304 stainless steel sheet caused by the above reasons, high-temperature solution treatment can be used to restore the austenite structure, which means transforming the martensite or ferrite into austenite and thus eliminating the magnetism.
It should be explicitly stated that the generation of magnetism in 304 stainless steel pipes due to the above reasons is a normal phenomenon. Duo Xing Stainless Steel Pipe Factory suggests that customers who purchase 304 stainless steel should not use this point to measure the quality of 304 stainless steel pipes.
