2024-11-22
Stainless steel-Why are some stainless steels magnetic?
Magnetism is fairly complex and is quantum mechanical in nature – this explanation is a simplified introduction. Within an atom, there are several layers of electrons at different energy levels. These energy states are called shells, and each shell can hold a discrete number of electrons. Each electron has an orbital spin of a certain orientation. If all electrons are paired with electrons of opposite spins, the “pull” of each electron is cancelled by its complement. Magnetic materials consist of atoms with only partially filled electron shells and a crystal structure that allows the alignments of electrons to be pulled into a particular preferred orientation. This combination of factors results in the densely packed FCC austenitic stainless steels being nonmagnetic.So, why would you choose one type of stainless steel over another? Cost and mechanical properties both play a role. For example, your flatware is most likely nonmagnetic or weakly magnetic, made from austenitic stainless steel. This type has good corrosion resistance (nobody would want to eat from rusty spoons), but due to the FCC structure that is stabilized by a high nickel content, cannot be hardened by heat treatment and can’t retain a sharp edge. Kitchen knives, by contrast, are usually made from magnetic martensitic stainless steel – it also has good corrosion resistance, but low to no nickel and higher carbon content, among other alloy additions, gives it hardenability through heat treatment and good sharp edge retention.