How can the magnetism of stainless steel welded pipes be identified?

How to identify the magnetism of stainless steel welded pipes?
Stainless steel welded pipes are also widely used in production. Many people only know that stainless steel welded pipes have anti-oxidation and anti-corrosion properties, but few know that stainless steel welded pipes can be magnetic. So, how to identify the magnetism of stainless steel welded pipes? It is mentioned that austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to component segregation during smelting or improper heat treatment, a small amount of martensite or ferrite structure may occur in austenitic stainless steel. Thus, stainless steel may have a weak magnetic property. Additionally, after cold working, the microstructure of stainless steel will transform into martensite. The greater the degree of cold working deformation, the more martensite transformation occurs, and the greater the magnetic property of the steel.

Just like the steel strips of the same batch, when producing Φ76 tubes, there is no obvious magnetic sensation. When producing Φ9.5 tubes, due to the larger cold-bending deformation, the magnetic sensation becomes more obvious. When producing square and rectangular tubes, the deformation is greater than that of round tubes, especially at the folded corners, where the deformation is more intense and the magnetic property is more obvious. To completely eliminate the magnetic property caused by the above reasons, high-temperature solid solution treatment can be carried out to restore the stable austenite structure, thereby eliminating the magnetic property. In summary, the magnetic property of stainless steel welded tubes caused by the above reasons is not at the same level as that of other stainless steel materials such as 430 and carbon steel. That is to say, the magnetic property of the steel always shows weak magnetism.

This tells us that if the stainless steel strip is weakly magnetic or completely non-magnetic, it should be identified as 304 or 316 material. If it shows strong magnetism like carbon steel, it should be identified as not being 304 material. The above points are explanations of the common magnetic properties of stainless steel welded pipes.