Is Stainless Steel Magnetic?
Stainless steel grades show excellent corrosion resistance due to the large chromium concentration in the chemical composition. Furthermore, the iron-based alloy can give these materials magnetic characteristics. However, since stainless steels represent a broad group of metals, the question of magnetic characteristics cannot be answered easily. To cut a long story short, some steel grades can be magnetized while others can not.
What makes steel grade magnetic?
For a steel grade to be magnetic, certain conditions must be met:
- The crystal structure of the steel needs to be arranged in either a martensitic or ferritic structure.
- The steel grade must contain a magnetic metal in it. Examples of magnetic metals are iron, cobalt or nickel.
Stainless steel contains no cobalt or nickel, but it contains iron per definition. Therefore, the second condition is always met. However, stainless steel can have a martensitic, ferritic or austenitic crystal structure, while only the first two have magnetic properties. Thus, stainless steels which are mostly composed of austenite are non-magnetic.
The magnetic properties of the different stainless steel grades
Steel can be differentiated in four groups. All of them show different magnetic characteristics.
Ferritic steels
As the name suggest, ferritic stainless steels contain a large amount of ferrite in their chemical composition. Since ferrite is comprised out of iron and other elements, ferritic stainless steels usually possess magnetic characteristics. It is the combination of iron and a ferritic crystal structure which gives this steel grade its characteristics. Typical ferritic steel grades with magnetic properties are 409, 430 and 439. However, it should be noted that the magnetic pull differs from grade to grade and some may have a weaker pull than normal carbon steel.
Martensitic steel
The unique crystal structure of martensitic steel grades combined with a chemical composition which includes iron make martensitic steel grades magnetic. Martensitic stainless steel grades such as 410, 420 and 440 can be magnetized.
Duplex steels
Duplex steels combine a phase balance of ferrite and austenite. The addition of ferrite to the mixture gives duplex steels its magnetic properties. However, the ratio of ferrite to austenite determines the magnetic properties of duplex steels. Steel grades with higher proportion of austenite are slightly less magnetic. Duplex steel grades such as 2205 possess magnetic characteristics.
Austenitic steel
Austenitic grades are known for their great corrosion resistance due to the high amount of chromium concentration in the alloy. However, although containing iron per definition, austenitic stainless steel grades show non-magnetic characteristics due to the high amount of austenite. Even steel grades such as 304 and 316 which mostly consist of iron, show non-ferromagnetic characteristics. Heat treatments or work-hardening, though, can change the crystal structure of austenitic steel grade. Hence, ferrite can form in some locations. This circumstance can make the metal partially magnetic.
Why do the magnetic properties of steel matter?
The magnetic characteristics of a steel grade can have a negative impact on the performance of the metal. Magnetic materials can cause issues when performing metal fabrication processes such as welding. Further, electrical currents are influenced by metals which are magnetic. On the other hand, magnetic materials can simplify processes like sorting.
