Most people assume that every type of stainless steel is magnetic. It’s all made from iron, right? However, different types of stainless steel have different levels of magnetism, generally due to the steel’s chromium level.
Ferritic vs Austenitic
Stainless steel is divided into two general types, which each have a different atomic structure. In general, ferritic stainless steel is magnetic, while austenitic types like 904L stainless steel are not. While both types of steel are iron alloys, there are critical differences in how their atoms are arranged that affect not just their levels of magnetic attraction but also other characteristics like their weldability.
In an austenitic stainless steel, the atoms are arranged in what is known as a face-centered cubic (fcc) lattice. Picture the unit cells as a cube: there are atoms at the centers of each of the cube’s faces and also at each of the eight corners of the cube. This sort of atomic arrangement is most likely to show up when the allow contains carbon, nitrogen, manganese or nickel.
Ferritic stainless steels, by contrast, are arranged in what is known as a body-centered (bcc) lattice. Atoms are arranged at each of the eight corners of the cube. Another single atom is located in the center of the cube. Silicon, chromium and molybdenum make a bcc crystal structure most likely.
The least magnetic steels
Stainless steel type 304, which contains 8% nickel and 18% chromium, along with small amounts of carbon, nitrogen and manganese make this steel nonmagnetic. What is interesting is that, when this steel is mechanically deformed through activities like bending or extruding, it will become partially magnetic.
Stainless steel type 904L is another popular nonmagnetic option. This type of steel contains high amounts of nickel and molybedenum, along with small amounts of carbon, manganese and phosphorus. In addition to being nonmagnetic, this type of steel is highly resistant to crevice corrosion and stress corrosion cracking. It’s highly weldable and formable.
Magnetized or Unmagnetized?
Ferritic steels typically start off unmagnetized. However, if they are exposed to a magnetic field, they will become magnetized. Even after being removed, they will remain magnetic to some degree. Nonmagnetic steels do not have this property, and can be exposed to magnetic fields without any risk that they will become magnetic after exposure.
Matching your steel choice to the job is imperative for assuring the performance that you want. We offer a range of stainless steel grades and types to ensure that you always have the exact alloy you need. Not sure what is best for your application? Get in touch. Our experts bring years of experience to the field and can help you pick the right steel for your application and your budget.