If you ask someone “is stainless steel magnetic?” you will likely get a variety of responses. Some people believe that stainless steel is a completely non-magnetic material. Others believe that stainless steel must be magnetic because it contains iron. However, like with most things, the answer lies somewhere in between. The fact is, some types of stainless steels are magnetic while others are not.
What Makes a Stainless Steel Magnetic?
In order for stainless steel to be magnetic, a couple of requirements need to be met:
- The stainless steel must have iron in it
- The stainless steel must have its crystal structure be arranged in a ferritic or martensitic structure.
First and foremost, since stainless steels are a type of steel, which means they must contain iron in their chemical composition. That takes care of the first requirement. The second requirement is that the stainless steel must have its crystal structure be arranged in a ferrite or martensite structure. If a stainless steel is mostly comprised of an austenite structure, then it will not be magnetic.
Which Types of Stainless Steel Are Magnetic?
Magnetic and non-magnetic stainless steels can typically be grouped together based on the type of stainless steel. The following types of stainless steel are typically magnetic:
- Ferritic Stainless Steels such as grades 409, 430 and 439
- Martensitic Stainless Steel such as grades 410, 420, 440
- Duplex Stainless Steel such as grade 2205
Ferritic Stainless Steels:
Ferritic stainless steels are typically magnetic as they have large quantities of ferrite in their chemical composition. Ferrite is a compound of iron and other elements. The combination of a ferritic crystal structure with iron makes ferritic stainless steels magnetic. However, some ferritic stainless steels may have a weaker magnetic pull than normal carbon steel.
Martensitic Stainless Steels:
Many martensitic stainless steels are magnetic. The unique crystal structure of martensitic steels can be ferromagnetic if iron is present. Since stainless steel is a type of steel, there is an abundant amount of iron in its make-up. This makes many martensitic stainless steels magnetic.
Duplex stainless steels:
Duplex stainless steels are typically magnetic because they contain a mixture of austenite and ferrite. The substantial amount of ferrite (which is magnetic) contributes to Duplex steels being magnetic. However, since duplex stainless steels have more austenite than ferritic steels, they may be slightly less magnetic.
Austenitic Stainless Steel:
Austenitic stainless steels have a high amount of austenite which makes them mostly non-magnetic. Even though grades such as 304 and 316 stainless steel have high amounts of iron in their chemical composition, austenite means they are non-ferromagnetic. However, if the crystal structure of an austenitic stainless steel is changed through work-hardening or special thermal treatment, then ferrite can form in some locations making the steel partially magnetic.
Why Does It Matter?
Magnetic material can have a huge effect on the intended performance of a material depending on its application. If a material needs to be quickly sorted from other materials, then having one material be magnetic can make this a very easy sorting process to carry out. When welding or performing other metal fabrication processes, magnetic material may cause issues to arise. Electrical currents can also behave differently in magnetic materials.
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