Is Stainless Steel Magnetic? It Depends on the Grade

Some stainless steel is magnetic and some is not. It comes down to the grade’s microstructure. Austenitic grades such as 304 and 316 are essentially non-magnetic when annealed, though cold working can give them a weak pull. Ferritic, martensitic, and duplex grades, including the 400 series, are magnetic.

That difference matters on the shop floor. A magnet can’t tell you which grade you have, and a 300 series part that sticks to one usually isn’t the wrong material. Here’s how stainless magnetism works and how to spec around it.

IS STAINLESS STEEL MAGNETIC?

Stainless steel is a family of alloys, and every one of them contains at least 10.5% chromium. That chromium forms a thin oxide layer that resists rust and re-forms when the surface gets scratched. It’s also why stainless steel holds up so well against rust, though it isn’t rust-proof.

Magnetism depends on how the atoms are arranged. Ferritic and martensitic stainless steels have crystal structures that respond to a magnet. Austenitic stainless steels have a different structure, held in place by nickel, that doesn’t. Duplex grades are roughly half ferrite and half austenite, so they also pull on a magnet, just less strongly than ferritic grades.

WHICH STAINLESS STEEL GRADES ARE MAGNETIC?

• Austenitic (300 series, such as 301, 302, 304, and 316): Essentially non-magnetic when annealed. Can become weakly to strongly magnetic after cold working, depending on the grade.
• Ferritic (such as 430): Magnetic.
• Martensitic (such as 410 and 420): Magnetic. These grades can be hardened, which is why they show up in knives and tools.
• Duplex (such as 2205): Magnetic.

What Makes Something Magnetic? 

But back to magnetism. In the case of steel, whether or not it is magnetic comes down to the microstructure of the steel. Basic stainless steels have what’s known as a “ferritic” structure, which enables them to be magnetic. Remember the chromium content? It’s the addition of chromium that leads to the ferritic structure. This, plus the addition of carbon, hardens the steel and qualifies it as a martensitic steel. Stainless steel knives are typically martensitic.

Martensitic steel differs from the most common stainless steels, which are referred to as austenitic. In austenitic steel, there is a higher percentage off chromium, and nickel is also present. In terms of magnetism, it is the addition of nickel that renders the steel non-magnetic. 

Can non magnetic stainless steel become Magnetic?

Yes. Cold working, such as rolling to a harder temper, bending, or stamping, turns some of the austenite in a 300 series grade into martensite, which is magnetic. Welding can also leave ferrite in the weld zone. The British Stainless Steel Association uses a stainless sink as the example. The flat drainboard barely responds to a magnet, while the pressed bowl pulls harder, especially in the corners where the metal was formed most.

How much pull you get depends on the grade. According to Atlas Steels’ technical note on magnetic response, 316 usually becomes only slightly magnetic, while 301 has less nickel and turns strongly magnetic after even a small amount of cold work. Annealing reverses the effect, though the part also gives up the strength the cold work added.

When magnetism is a dealbreaker, as in MRI equipment, customers and suppliers often agree on a maximum magnetic permeability before the order ships.

DOES Mead Stock Non-Magnetic Stainless Steel?

Yes. We stock 300 series austenitic stainless steel, including 301 and 302/304. Keep in mind that hard tempers are cold worked by definition, so a full hard 301 spring strip will respond to a magnet.

If magnetic response matters for your part, tell us up front. Our inside sales team will help you land on the grade and temper that fit, in the quantity you actually need.

Get a Quick Quote for your steel order.

FREQUENTLY ASKED QUESTIONS

IS 304 STAINLESS STEEL MAGNETIC?

In the annealed condition it is essentially non-magnetic. Cold working, such as rolling to a harder temper, can make it slightly magnetic, and that does not mean the grade is wrong. Welds and bent areas can also pick up a weak pull.

IS 316 STAINLESS STEEL MAGNETIC?

Like 304, annealed 316 is essentially non-magnetic. Cold working can add a slight magnetic response, though 316 generally stays less magnetic than 304 because of its higher nickel content. A weak pull does not mean the part is mislabeled.

WHY DOES MY STAINLESS STEEL PART STICK TO A MAGNET?

Three things usually explain it. Cold working can make a 300 series grade weakly magnetic. A 400 series grade is magnetic by design, and iron contamination on the surface can do the pulling too.

CAN YOU USE A MAGNET TO TELL 304 FROM 316?

No. Both are austenitic grades and respond to a magnet in much the same way. The mill test report shows the chemistry of your lot, and a handheld analyzer can confirm it on a finished part.