Is Stainless Steel Magnetic?

In truth, this query is far trickier to resolve. That’s because there are various different types of stainless steel. Depending on the concentration of different metals in their composition, some of them are magnetic and some are not. As such, it’s important to verify whether magnetism is a priority for you, then make your decision on which type and grade to purchase for your project.

If that all sounds a little confusing, don’t worry. In the article below, we’ll give you a comprehensive overview of the issue in simple and easy-to-understand terms.

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.

Today, there are almost 60 different grades of standard stainless steel alloy, each of which has been developed to accentuate different attributes. What’s more, 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.

Having said that, stainless steels can be broadly divided into three main categories. These are austenitic stainless steel, ferritic stainless steel and martensitic stainless steel. So, how do these types of steel relate to the question, “is stainless steel magnetic?” Well, in order for a stainless steel to be magnetic, it must:

• Contain iron
• Possess a ferritic or martensitic crystal structure

Generally speaking, ferritic stainless steels are magnetic. This is 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.

There are a number of different grades of martensitic stainless steels, three of which (410, 420 and 440) are magnetic. This is because iron is the main component in the alloy, creating a ferromagnetic crystal structure which creates the 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.

Because austenitic stainless steels generally contain more austenite than ferrite, they are usually non-magnetic. Although grades like 304 and 316 do contain iron, their crystal structure does not lend itself to magnetism. Having said that, austenitic alloys can be treated (by bending, drilling or heating) to form ferrite, making them partially magnetic.

To understand which grade of stainless steel will best serve your purposes, it’s first important to think about what you require from it. For industrial applications, strength and chemical- or corrosion-resistance might be the priority. In kitchen environments, its ability to withstand high temperatures, humidity levels and acid exposure could be paramount. For other projects, magnetism may be the deciding factor.

Once you know what you’re looking for from your stainless steel, you can then begin the process of elimination for which grade to choose. That’s because some types of the alloy 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 example, some (like 316) are better at withstanding water exposure than others (304).

The best course of action may be to make a list of the properties you prioritise in stainless steel, then cross-reference that against the different attributes of each grade. Of course, that potentially means a substantial amount of legwork, which is why it can help to seek advice from trained professionals, who can use their expertise to choose the right alloy for you.