NONMAGNETIC STEEL-manganese-nickel-chromium steelsSteel and iron alloys used where magnetic effects cannot be tolerated. Manganese steel containing 14% manganese is nonmagnetic and casts readily but is not machinable. Nickel steels and iron-nickel alloys containing high nickel are also nonmagnetic. Many mills regularly produce nonmagnetic steels containing from 20 to 30% nickel. Manganese-nickel steels and manganese-nickel-chromium steels are nonmagnetic and may be formulated to combine desirable features of the nickel and manganese steels. One nonmagnetic steel with a composition of 10.5 to 12.5% manganese, 7 to 8 nickel, and 0.25 to 0.40 carbon has low magnetic permeability and low eddy-current loss, can be machined readily, and work-hardens only slightly. The tensile strength is 80,000 to 110,000 lb/in2 (552 to 758 MPa), elongation 25 to 50%, and specific gravity 8.02. It is austenitic and cannot be hardened. The 18–8 austenitic chromium-nickel steels are also nonmagnetic. A nonmagnetic alloy used for watch gears and escapement wheels is not a steel but is a copper-nickel-manganese alloy containing 60% copper, 20 nickel, and 20 manganese. It is very hard, but can be machined with diamond tools.
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