We can determine whether the pipe is 304 stainless steel pipe through magnetic

[guidebook] : In our daily life, we often judge the quality of stainless steel by whether the pipes are magnetic or not, but in fact, this method of pipes is very unscientific...

In our daily life, we often judge the quality of stainless steel by whether the pipes are magnetic or not, but in fact, this method of pipes is very unscientific. For example, our common zinc pipe alloys and copper pipe alloys can usually mimic the appearance and color of stainless steel, and they are not magnetic. Whatever the rusty steel is, it can easily be mistaken for something else. Even the most commonly used pipeline 304 steel at present, there will be different degrees of pipeline magnetism after cold working, so the quality of stainless steel can not be judged by whether there is a magnetic pipe or not, so why is 304 stainless steel pipe magnetic.

Generally speaking, pipeline stainless steel can be divided into two categories according to the organizational structure at room temperature: one is pipeline austenitic stainless steel, such as 304321 pipe, 316 pipe, 310 pipe and so on. ; The other is pipeline martensitic or ferritic stainless steel, such as 430420 pipe, 410 pipe and so on. ; Austenitic stainless steel pipe is non-magnetic or weakly magnetic, while martensite or pipe ferritic is magnetic, so 304 stainless steel pipe is non-magnetic, if magnetic.

We often say that 304 stainless steel is non-magnetic tubular stainless steel, which means that its magnetic index is below a certain value. That is to say, in general, stainless steel has more or less certain pipe magnetism. The previously mentioned austenitic stainless steel is non-magnetic or weakly magnetic, while ferritic and martensitic stainless steel is magnetic tubular, which is due to compositional segregation or improper heat treatment in the melting process, resulting in a small amount of martensitic or ferrite structure in austenitic 304 stainless steel. In this way, 304 stainless steel pipe will appear weakly magnetic. In addition, after cold processing, the microstructure of 304 stainless steel pipe will also be transformed into martensite. The greater the cold pipe processing deformation, the more martensitic phase transition pipe, the stronger the magnetism.

Therefore, the magnetism of the material depends on the regularity of the molecular arrangement of the tube and the isotropy of the electron spin, which can be regarded as the physical properties of the material tube, and the corrosion resistance of the material depends on the chemical composition of the material tube, which is the chemical properties of the material tube, and has nothing to do with whether the material tube is magnetic.