Is It Possible To Judge The Quality Of Magnetic Stainless Steel Is unqualified?

Most people think that magnetic stainless steel is bad, and use magnets to judge the quality of stainless steel pipe and fittings. It is definitely unscientific.

There are many types of stainless steel, which can be divided into several categories according to the organizational structure at room temperature:

• Austenite type such as 304, 321, 316, 310, etc.;
• Martensite or ferrite type such as 430, 420, 410, etc.;
  

The austenitic type is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic.

Why some stainless steels magnetic

The stainless steel commonly used for decorative tubes/plates is mostly austenitic 304, which is generally non-magnetic or weakly magnetic. However, due to chemical composition fluctuations or different processing conditions caused by smelting, magnetism may also appear, but this cannot be considered It is unqualified. What is the reason?

As mentioned above, austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to component segregation or improper heat treatment during smelting, a small amount of martensite or ferrite in austenitic 304 stainless steel will be caused. In this way, 304 stainless steel will have weak magnetic properties.

After 304 stainless steel is cold treated, the structure will also transform to martensite. The greater the degree of cold working deformation, the more martensite transformation and the greater the magnetic properties of the steel. (e.g. For pipes made of the same material, for Φ76 pipes, no obvious magnetic induction, for Φ9.5 pipes, the magnetic induction is more obvious due to greater deformation). To completely eliminate the magnetism of 304 steel caused by the above reasons, it can be passed high temperature solution treatment restores the stable austenite structure, thereby eliminating magnetism.

Can I judge stainless steel type by magnetism

It is particularly emphasized here that the magnetism of 304 stainless steel caused by the above reasons is not at the same level as other materials of stainless steel, such as 430 and carbon steel.

That is to say, the magnetism of 304 steel always shows weak magnetism. If the stainless steel has weak magnetism or no magnetism at all, it should be judged as 304 or 316 material; if the magnetism is the same as carbon steel, it shows strong magnetism, because it is judged as not 304 material.