Is Stainless Steel Magnetic?

Though this may seem like a simple question, there are in fact three answers: yes, no and sometimes! All stainless steels contain iron, which is magnetic. So why are all stainless steels not magnetic? Let's take a deeper dive into this fascinating subject and try to put paid to any confusion you may have.

The magnetism of stainless steel or indeed any other metal is important as it can have major effects on that metal's performance depending on the application it is used for. It is, for example, an excellent quality to have when sorting magnetic from non-magnetic materials quickly and efficiently. It can, however, cause problems when welding, as a magnetic field can interfere with welding sparks resulting in poor welds. Magnetism also affects the way in which electrical currents travel through a material.  

Stainless steel alloys are divided into several different 'types', which are distinct from the 'grades' that each different type is sub-divided into. The type of stainless steel is dependent on its chemical composition, which in turn dictates its crystal structure.

Austenitic Stainless Steel
Austenitic is the most widely-used type of stainless steel, especially common grades like 316 and 304. They contain high levels of the iron allotrope austenite, which alters their chemical structure and offsets ferrites in the stainless steel, causing austenitic stainless steel to be non-magnetic. 

Work hardening and thermal treatments can cause ferrite to form, making austenitic stainless steels partially magnetic. This is why the edges of stainless steel sheet sometimes exhibit slight magnetism. 

Ferritic Stainless Steel
Ferrite is a compound containing a high level of iron, giving this type a ferritic structure and making it magnetic. Common grades of ferritic stainless steel include 439, 430 and 409, all of which display different strengths of magnetic pull.  

Martensitic Stainless Steel 
Another type with a high level of iron, the vast majority of martensitic stainless steels are magnetic. This type includes common grades like 440, 420 and 410. 

Duplex Stainless Steel
Duplex stainless steels are becoming increasingly popular as they are easy to fabricate and offer enhanced corrosion resistance. They are often more cost-effective because they do not contain nickel, an element which continues to rise in price as global demand increases. Duplex stainless steel contains both austenite and ferrite; the inclusion of austenite makes this type less magnetic than ferritic or martensitic stainless steel. 

Choosing the right type and grade of stainless steel is crucial and, if you're not sure, it's always best to check with our skilled technical team here at BS Stainless. Please browse our website for further information and do not hesitate to get in touch if you have any questions or need expert advice.