Why 304 stainless steel pipe is magnetic when used

In life, we often use the magnetism of tubes to judge whether stainless steel is good or bad, but in fact, this method is very unscientific. For example, our common zinc tube alloys and copper tube alloys can imitate the appearance and color of stainless steel, and they are also not magnetic, which is easy to be mistaken for stainless steel. Even the 304 steel that we currently use most often, after cold working, There will also be different degrees of pipe magnetism, so we can’t judge whether the stainless steel is good or bad by whether there is a magnetic pipe. Then why 304 stainless steel pipe is magnetic.

In general, industrial stainless steel welded pipe can be divided into two types according to its structure at room temperature. One is austenitic stainless steel pipe, such as 304321 pipe, 316 pipe, 310 pipe, etc., and the other is pipe martensite or ferritic stainless steel pipe, such as 430420 pipe, 410 pipe, etc., while austenitic stainless steel pipe is non-magnetic or weak magnetic, martensite or pipe ferrite is magnetic, So 304 stainless steel pipe is tubeless magnetic or with if magnetic.

We often say that 304 stainless steel is non-magnetic tubular stainless steel, which means that its magnetic index is lower than a certain value. That is to say, stainless steel generally has a certain degree of tube magnetism. The austenitic stainless steel that was lifted before is non-magnetic or weak magnetic, while ferritic and martensitic stainless steel have magnetic tubular properties, which is due to the composition segregation or improper heat treatment tubes during smelting, This causes a small amount of martensite or ferrite structure in the austenitic 304 stainless steel, so that weak magnetism will appear in the 304 stainless steel tube. In addition, after cold processing, the structure of 304 stainless steel tube will also be transformed into martensite. With the greater deformation of cold tube processing, the more martensite conversion tubes, the stronger the magnetism will be.

Therefore, the magnetic properties of materials are determined by the regularity of the molecular arrangement of tubes and the isotropy of electronic spin, which can be considered as the physical properties of materials, while the corrosion resistance of materials is determined by the chemical composition of materials, which is the chemical properties of materials and tubes, and has nothing to do with whether the materials are magnetic or not.


Post time: Aug-17-2023