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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.
Chromium, molybdenum and silicon make it more likely that the alloy will exhibit the bcc crystal structure at room temperature.
The most popular stainless steel is Type 304, which contains approximately 18 percent chromium and 8 percent nickel. At room temperature, the thermodynamically stable crystal structure of 304 stainless steel is bcc;
maintains an fcc structure and therefore the alloy is nonmagnetic. If the alloy is mechanically deformed, i.e. bent, at room temperature, it will partially transform to the ferritic phase and will be partly magnetic, or ferromagnetic, as it is more precisely termed.
Popular ferritic stainless steels are iron-chromium binary alloys with 13 to 18 percent chromium. These alloys are ferromagnetic at room temperature. Like all ferromagnetic alloys, when heated to a high enough temperature--their Curie temperature--the ferritic stainless steels lose their ferromagnetism and become paramagnetic--that is, they do not retain their own magnetic field but continue to be attracted to external ones. Statistics: Posted by waterbard — Tue Nov 21, 2006 11:49 pm
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