Nonmagnetic Materials

paramagnetic, diamagnetic, and weakly ferromagnetic materials with magnetic permeability μ≦ 1.5. Nonmagnetic materials include most metals and alloys, polymers, wood, and glass.

Metallic nonmagnetic materials—mainly nonmagnetic steels and cast irons, but also alloys of copper and aluminum—are most commonly used because of their good mechanical properties, wear resistance, and durability. Steels and cast irons are made nonmagnetic by producing austenitic structure in them; this is achieved by suitable alloying. Chrome-nickel nonmagnetic steels produced in the form of sheets, wire, and strips have the best processing properties. The typical composition and properties of a nonmagnetic steel with high corrosion resistance are as follows: up to 0.12 percent carbon, up to 0.8 percent silicon, 1–2 percent manganese, 17–19 percent chromium, and 11–13 percent nickel; μ = 1.05–1.20; tensile strength, 500–600 meganew-tons per sq m, or 50–60 kilograms-force per sq mm; ultimate elongation, 40–50 percent. Less expensive nonmagnetic cast irons, whose specific electric resistance (1.4—2.0 microhms . m [μ Ω • m]) is usually greater than that of nonmagnetic steels (about 1 μ Ω • m), are used for parts of complex shape that do not require high strength; this results in low eddy-current losses in parts operating on alternating current. Nickel-manganese cast irons containing 2.6–3.2 percent carbon, 5.0–7.5 percent manganese, 9–12 percent nickel, 2.5–3.5 percent silicon, and up to 1.1 percent phosphorus, with μ = 1.03–1.06, which are well suited for cutting, are most common.

Nonmagnetic materials based on nonferrous metals usually have lower magnetic permeability than nonmagnetic steels and cast irons, and they readily undergo cutting and pressure working. However, their mechanical properties are not always satisfactory, and their electric resistance is low.

Nonmagnetic materials are used for the production of parts that must not exert a magnetic effect on the operating system of measurement devices, instruments, and machines. They are used to make compass cases, parts for electrical measurement instruments and clocks, nonmagnetic springs, periscope tubes, bushings and collars through which pass cables carrying alternating current, and clamp bolts and housings for transformers and electric machines.