FAQ: Is 304 Stainless Steel Magnetic?

A few times a year at Component Supply, we get a call or email from a customer who is confused or frustrated that the 304 tubing or wire they’ve purchased, either from us or somewhere else, is acting magnetic.

“304 is not supposed to be magnetic!”

We understand the frustration that can come when a complicated concept, like magnetism, is oversimplified. The truth is, usually, 304 does not act magnetic, but there are many factors that can affect magnetism in 300-series alloys.

Our most commonly requested alloys, 304 and 316 stainless steel, are austenitic, so theoretically non-magnetic, but 300-series stainless steel is practically non-magnetic *ONLY* after it is freshly formed. 304 and 316 always possess paramagnetic characteristics, meaning small particles can be attracted to powerful magnetic separators and, depending on their weight, can be held to magnets during production. Fun fact: 304 is always slightly more magnetic than 316.  

In addition to stainless steel’s inherent traits that affect magnetism, there are also environmental elements to consider. Exposure to chemicals, intense mechanical processes, extreme high (or low!) temperatures, etc. can change the crystal structure of stainless steel and convert it to the ferromagnetic martensite or “ferrite” (Ferrite=magnetic) forms of iron. For instance, cold-working (stamping, forming, polishing) will probably cause 304 to become magnetic because initially the cold work causes the stainless steel to pick up foreign particles, like free iron, and the areas that have picked up those particles change the crystal structure. Then, *bonus feature* areas that are magnetic then become more prone to rust in a corrosive environment. (You can also check out our “why is my stainless steel rusting?” post for more information).

When we hear “but stainless steel is not magnetic,” we usually ask our customers, “well, what did you do to it?” We want to make sure we can rule out those environmental variables. We are happy to review material certificates along with other factors any time you have an issue, but often there is some process – the “environmental variable” – that has changed the structure of the alloy to cause magnetism.

So is stainless steel magnetic? Well, it just depends on what you’re doing to it.