Is Stainless Steel Magnetic?
Today we are getting to the bottom of another myth in the world of materials. There is a widespread assumption that stainless steel is not magnetic. But that is not quite correct. We explain when and why stainless steel is magnetic.
Is Stainless Steel Magnetic? The Most Important Points in Brief
- Stainless steel is not generally non-magnetic: Whether stainless steel is magnetic depends on alloy, composition and processing.
- Ferritic and martensitic stainless steels are magnetic, while austenitic chromium-nickel steels usually are not.
- Cold forming or deformation can make originally non-magnetic stainless steel magnetic, e.g. through bending, straightening or cutting.
- A simple magnet test is not always sufficient: Precise statements are only possible through material analysis or the material number.
- Magnetic stainless steel is not inferior, but necessary for many applications, for example induction hobs.
When Is Something Considered Magnetic?
Here we need to take a closer look at the term ferromagnetism. Materials with corresponding properties are attracted by a magnet and can themselves be magnetised, whereby the magnetisation may partially remain even after the external magnetic field has been removed.
Whether a metal is magnetic depends largely on its microstructure. In stainless steel, ferritic and martensitic structures are generally magnetic, while austenitic stainless steels usually have no magnetic effect. A simple magnet test can provide an initial assessment, but it does not replace precise material analysis.
And When Is It Considered Non-Magnetic?
And when is a material considered non-magnetic? In this context, paramagnetism is decisive. Materials with these properties show no measurable magnetisation without an external magnetic field. Only in the presence of an external magnetic field can a very weak magnetisation be detected by measurement.
However, since a conventional fridge magnet shows no attraction here, these materials are referred to as non-magnetic in everyday use. Materials with such properties include aluminium, chromium, platinum and austenitic stainless steel.
Magnetisable or Not?
Of the roughly 120 common stainless steel grades, only some are magnetic. Within stainless steels, a distinction is made between ferritic and martensitic steels (chromium steel), austenitic steels (chromium-nickel steel) and duplex steels. Whether a stainless steel is magnetic, non-magnetic or magnetisable depends largely on its composition and iron content.
Ferritic and martensitic stainless steels have a chromium content of around 12 to 18 percent and often show magnetic behaviour. Austenitic stainless steels are the most common stainless steels. In addition to chromium, they also contain nickel, which generally makes them non-magnetic and at the same time increases their corrosion resistance.
Duplex steel is created by combining both types of steel and combines their characteristics, which means that both magnetic and non-magnetic forms can occur.
Frequently Used Stainless Steels in Practice
70 % of all stainless steels used worldwide are chromium-nickel steels, i.e. austenites, and therefore not magnetisable. However, if you look more closely, most chromium-nickel steels are not fully austenitic. In material reality, V2A and V4A grades show certain proportions of ferrite, known as delta ferrite. Proportions of up to 10 % delta ferrite are quite common here. In everyday terms, however, this is usually not enough to make the material noticeably magnetisable.
So How Do You Magnetise the “Non-Magnetic” Stainless Steels?
So how do you magnetise the supposedly “non-magnetic” stainless steels? Targeted force can change the microstructure, causing even chromium-nickel steel to become magnetic. Even slight deformation, for example during bending or straightening, is enough to trigger this effect.
During such cold working, the originally austenitic structure partially transforms, forming ferromagnetic deformation martensite. This process is called cold forming. The material is then deformed in the affected areas and reacts noticeably there to standard magnets, such as a fridge magnet.
Such locally magnetic zones often occur on tubes, screws or cut edges of stainless steel plates.
Conclusion: Is Stainless Steel Magnetic?
In summary, the myth of stainless and non-magnetic stainless steel is false. Rather, it depends on factors such as composition, alloy and processing whether a stainless steel is magnetic or not. If you are now wondering what magnetic stainless steel is needed for at all, think of your kitchen. If you have an induction hob, your cooking pots have strongly magnetised bases. They can heat up extremely quickly - all thanks to magnetic stainless steel.
Frequently Asked Questions
How can stainless steel be identified?
Stainless steel can be identified, among other things, by its chemical composition. In practice, methods such as an X-ray spectrometer are used to precisely determine the alloying elements it contains. In addition, assignment to specific stainless steel grades enables clear classification in terms of composition and typical areas of application.
Which stainless steel is magnetic and which is not?
Whether stainless steel is magnetic depends on the respective alloy. Clear assignment is possible via the material number, as it provides information about the microstructure type and magnetic behaviour. Austenitic steels are generally considered non-magnetic, while ferritic and martensitic variants can react magnetically. The decisive factor is the magnetic permeability of the material.
Is stainless steel of lower quality if it is "magnetic"?
No, magnetic behaviour says nothing about quality. Depending on the application, magnetic or non-magnetic stainless steels are deliberately used. The decisive factors are mechanical requirements, corrosion behaviour and the operating environment – not magnetisability alone.
Is stainless steel generally non-magnetic?
Stainless steel is not generally non-magnetic. Whether stainless steel is magnetic depends on alloy, composition and processing.
Which stainless steels are magnetic?
Ferritic and martensitic stainless steels are magnetic, while austenitic chromium-nickel steels are usually not magnetic.
Can non-magnetic stainless steel become magnetic through deformation?
Yes. Cold forming or deformation can make originally non-magnetic stainless steel magnetic, for example through bending, straightening or cutting.
Is a simple magnet test sufficient to determine stainless steel?
A simple magnet test can provide an initial assessment, but it does not replace precise material analysis or assignment via the material number.
