2024-11-22
Stainless steel-Why don't magnets work on some stainless steels?
Stainless steels are iron-based alloys primarily known for their generally excellent corrosion resistance, which is largely due to the steel's chromium concentration. There are several different types of stainless steels. The two main types are austenitic and ferritic, each of which exhibits a different atomic arrangement. Due to this difference, ferritic stainless steels are generally magnetic while austenitic stainless steels usually are not. A ferritic stainless steel owes its magnetism to two factors: its high concentration of iron and its fundamental structure. The metallic atoms in an austenitic stainless steel are arranged on a face-centered cubic (fcc) lattice. The unit cell of an fcc crystal consists of a cube with an atom at each of the cube's eight corners and an atom at the center of each of the six faces. In a ferritic stainless steel, however, the metallic atoms are located on a body-centered (bcc) lattice. The unit cell of a bcc crystal is a cube with one atom at each of the eight corners and a single atom at the geometric center of the cube. Alloying the stainless steel with elements such as nickel, manganese, carbon and nitrogen increases the likelihood that the alloy will possess the fcc crystal structure at room temperature. Chromium, molybdenum and silicon make it more likely that the alloy will exhibit the bcc crystal structure at room temperature.