How to recognize stainless steel grade 304 by magnetic properties of stainless steel

People used to use magnets to verify whether the quality of stainless steel is good or not. They believe that if it is magnetic, it is good enough and vice versus. Actually, this is a wrong way to identify the quality of stainless steel.

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

  • Austenite stainless steel such as grades 304, 321, 316, 310;
  • Martensite or ferrite stainless steel such as grades 430, 420, 410;

Austenite stainless steel is non-magnetic or weakly magnetic, while martensite or ferrite stainless steel is magnetic. Most stainless steel for decoration is made from austenitic grade 304, which is theoretically non-magnetic or weakly magnetic. However, magnetic properties may also occur due to fluctuations in chemical composition or different processing conditions caused by smelting.  And magnetic properties cannot be considered counterfeit or unqualified. What is the reason for this?

As what we have mentioned above, austenite stainless steel is non-magnetic or weakly magnetic, while martensite or ferrite stainless steel is magnetic. If the crystal structure of an austenitic stainless steel is changed through work-hardening or special thermal treatment, then ferrite can form in some locations making the steel partially magnetic. 

In addition, as the process of cold working of stainless steel grade 304, and the structure will also be transformed to martensite. The greater the degree of cold working deformation, the more martensite transformation, and the greater the magnetic properties of the steel.

However, noted that the magnetic properties of stainless steel grade 304 due to the above reasons are completely different from those of other materials such as stainless steel grade 430 and carbon steel. That is to say the magnetic properties of stainless steel grade 304 always shows weak magnetic properties.

So if stainless steel is weakly magnetic or completely non-magnetic, it should be judged as stainless steel grade 304 or 316, while if it is as magnetic as carbon steel,that is, shows strong magnetism, it may not be judged as stainless steel grade 304.

Although there are various ways to verify what the material is, for customers, it may be still difficult to find out whether it is what you want. Therefore, it is crucial to choose a reliable supplier. Haixu Co., Ltd. is specialized in stainless steel and even decorative sphere for over 20-years experience. We boast our high quality and the service of OEM and customization. 👉 Get to know us: