2024-11-22
Stainless steel-How Nonmagnetic are 304 and 316 Stainless Steels?
Both 316 and 304 stainless steels are austenitic; when they cool, the iron remains in the form of austenite (gamma iron), a phase of iron which is nonmagnetic. The different phases of solid iron correspond to different crystal structures. In other alloys of steel, this high-temperature phase of iron transforms to a magnetic phase when the metal cools. The presence of nickel in the stainless steel alloys stabilizes austenite against this phase transition as the alloy cools to room temperature. As a result, a relative permeability of K ∼ 1.002 to 1.005 are typically reported for 304 and 316 stainless steels in their annealed state. This corresponds to a somewhat larger magnetic susceptibility than we might expect for other nonmagnetic materials, but is still well below what might be considered magnetic.