Is Stainless Steel Magnetic? Yes and No – Here’s Why

The answer isn’t as straightforward as a simple yes or no. The magnetic properties of stainless steel depend on its composition and structure. Some types of stainless steel are magnetic and others aren’t. Let’s break down why that is, no fluff.

Stainless steel is a metal alloy containing a blend of carbon, chromium, iron, nitrogen, manganese and silicon. While the exact variations of these substances will vary between grades of stainless steel, there are certain thresholds that they must meet in order to qualify the steel as stainless.

For example, the carbon content of the alloy cannot exceed 1.2%, while it must contain at least 10.5% chromium. If it does not, it is steel, but it is not stainless steel. That’s because chromium (mixed with nickel) is the key factor in preventing the metal from rusting, creating its stainless qualities.

Having said that, stainless steel is not completely impervious to rust. This is because the iron content of the alloy can eventually rust if given enough time and exposure. However, the act of adding chromium to the alloy – a process called passivation – greatly slows this corrosion down and extends the life of the alloy.

Steel is primarily composed of iron, which is a ferromagnetic material. That means iron naturally has magnetic properties because its atoms align in a way that generates a magnetic field.

When you add other elements like nickel, chromium and carbon to iron, you can change the atomic structure and, in turn, its magnetic behaviour. In simple terms, the more nickel and chromium added to the steel, the less magnetic it becomes. This is why some steel grades are magnetic while others aren’t.

Understanding how magnetism works in steel is important for selecting the right material for your project, especially in applications where magnetism plays a role – from electronics to construction.

Today, there are almost 60 different grades of standard stainless steel alloy, each of which has been developed to focus on different attributes. And manufacturers are creating new customised blends all the time, so it’s easy to see why there is such variation from one grade to another.

For a stainless steel to be magnetic, it must:

• Contain iron
• Possess a ferritic or martensitic crystal structure

The magnetic characteristics depend on the combination of elements in the steel and how they affect its internal structure. Broadly speaking, stainless steels can be divided into three main categories – austenitic, ferritic and martensitic – each with different magnetic behaviours.

Generally speaking, ferritic stainless steels are magnetic. That’s due to the high levels of ferrite (a compound of iron and other elements), which gives the material its magnetic qualities. While some ferritic stainless steels only give off a weak magnetic field, grades such as 409, 430 and 439 are magnetic stainless steels.

Grades like 430 have a high percentage of chromium and little to no nickel. The result is a body-centred cubic (BCC) structure, which allows the material to retain magnetic properties. Because of this, ferritic stainless steel is magnetic and can be attracted to magnets.

Ferritic stainless steel is often used in automotive parts, industrial applications and where corrosion resistance is necessary but magnetism is not an issue. It’s also less expensive than austenitic stainless steel, which makes it a popular choice if you don’t want to break the bank.

There are lots of different grades of martensitic stainless steels. Three of them (410, 420 and 440) are magnetic. This is because iron is the main component in the alloy, creating a ferromagnetic crystal structure that generates a magnetic field.

The carbon content of martensitic alloys means they can be hardened for extra strength, but this involves a trade-off with reduced chemical resistance compared to other grades.

This type of stainless steel is often used in applications like kitchen cutlery, medical instruments and tools where both strength and magnetism are required. It’s also heat treatable, allowing for additional strengthening.

Austenitic stainless steel is the most common type, found in items like kitchen appliances, medical equipment and food processing machinery. Because austenitic stainless steels generally contain more austenite than ferrite, they are usually non-magnetic. This grade also contains high amounts of nickel and chromium, which stabilise the face-centred cubic (FCC) structure of the metal.

Although grades like 304 and 316 do contain iron, their crystal structure does not lend itself to magnetism. This prevents the electrons from aligning in a way that creates a magnetic field, making austenitic stainless steel non-magnetic under normal conditions.

But there’s a catch – austenitic stainless steel isn’t always non-magnetic. Austenitic alloys can be treated (by bending, drilling or heating) to form ferrite, making them partially magnetic. So, while new austenitic stainless steel (like 304 and 316) won’t attract magnets, it can develop a bit of magnetism if it goes through deformation or cold rolling.

The short answer is that it depends on the type of stainless steel. Magnets will stick to ferritic and martensitic stainless steel because these alloys retain magnetic properties due to their internal structures. On the other hand, austenitic stainless steel, such as grades 304 and 316, is generally non-magnetic because of its atomic arrangement.

This isn’t a hard and fast rule though. While new austenitic stainless steel won’t attract magnets, external factors can cause it to develop weak magnetic properties, as mentioned earlier. So, while a magnet may not stick to a brand-new 304 stainless steel sheet, it might exhibit some magnetism after being bent or stretched.

If you're dealing with a piece of stainless steel and need to confirm whether it’s magnetic, a simple magnet test can do the job. Here’s how to perform it:

• Grab a strong magnet – The stronger the magnet, the easier it will be to detect magnetic properties.
• Place the magnet near the surface – Gently move the magnet along the surface of the steel.
• Observe – If the magnet sticks or strongly attracts to the surface, you’re likely working with ferritic or martensitic stainless steel. If the magnet does not stick or only has a weak attraction, the steel is probably austenitic.

For more accurate measurements, industrial testing methods such as magnetic permeability meters or eddy current testing can provide precise results, especially if you're dealing with thicker or more complex materials.

If you want to know which grade of stainless steel is best for you, the first step is to think about what you need from it. For industrial applications, strength and chemical- or corrosion-resistance might be top of the list. In kitchen environments, its ability to withstand high temperatures, humidity levels and acid exposure could be the one. For other projects, magnetism may well be the deciding factor.

Once you know what you’re looking for from your stainless steel, you can then start a process of elimination for which grade to choose. Some alloys are better at certain jobs than others. For example, austenitic alloys rarely offer magnetism, but they compensate for that by providing greater strength. Even within the grades, there are differences. For instance, 316 is better at withstanding water exposure than 304.

Here’s a quick breakdown of how magnetism matters when choosing stainless steel for different applications:

• Medical equipment and food processing: Non-magnetic materials like austenitic stainless steel are required in these industries to avoid interference with sensitive equipment or to prevent contamination.
• Kitchenware and cutlery: Martensitic stainless steel is often preferred for knives and utensils, as it offers the magnetic properties needed for handling and durability.
• Automotive and industrial applications: Ferritic and martensitic stainless steel are commonly used because their magnetic properties can aid in various manufacturing processes.