Alloys with high electrical resistance: features and applications

Alloys with high electrical resistance are used for the manufacture of heating elements for industrial equipment and household appliances, temperature sensors, resistors and strain gauges, critical elements of vacuum devices and connectors in electrical products. They are made on the basis of nickel (Ni), chromium (Cr), molybdenum (Mo), aluminum (Al) and iron (Fe). During production, they look like cold-rolled strip, strip, rod or wire. ‍

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Classification of alloys with high electrical resistance

Alloys with high electrical resistance are divided into groups according to their purpose and composition:

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• alloys for heating elements based on iron, chromium and aluminum — retain high heat resistance in vacuum, hydrogen, sulfur and carbon-containing media; under continuous exposure to high temperatures, they are prone to deformation;
• materials for nickel-chromium-based heaters — have high resistance to oxidation and deformation at elevated temperatures in vacuum, hydrogen, nitrogen and ammonia; in sulfur and sulfur compounds, the heat resistance of metals decreases;
• alloys for the manufacture of precision resistors are characterized by the dependence of the conductor's resistance on changes in its temperature; they may contain tungsten, manganese, chromium, nickel, aluminum, copper, beryllium, molybdenum, and vanadium.

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Regardless of the base composition, heater alloys do not oxidize and retain high heat resistance in atmospheres with excessive oxygen content.

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Steel grades and production features

The following steel grades are used for the manufacture of electric stove heaters and heating elements for household appliances:

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• X15Yu5, X23Yu5, X23Yu5T and X27Yu5T are precision alloys based on chromium-aluminum. In accordance with GOST 10994-74 “Precision alloys. Brands” should be used in their production with fresh charge materials. In the presented steels, except for X23U5T, no more than 0.1% zirconium is allowed.
• HN60UZ, HN70U, X15N60-N, X15N60UZA, X20N80-N and HN20YUS are nickel-chromium compounds. According to GOST 10994-74, X15N60-N and X20N80-N steels must be manufactured in induction or plasma furnaces (if the latter have a ceramic crucible).

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H2ON80 steels may contain residual calcium, magnesium, barium and REE (rare earth elements). In X20H80-VI, the presence of zirconium and REZ is considered a sign of marriage.

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Properties of alloys with high electrical resistance

One of the requirements for alloys with high electrical resistance is high plasticity. This makes it possible to produce wire with a cross section of 0.02 mm and a tape with a thickness of 0.01 mm or more from them.

In addition, all precision steels of this class, except those intended for the manufacture of resistors, have minimal electrical resistance fluctuations along the entire length of the heating element and a high maximum operating temperature (depending on the steel grade, it can reach +1,100°C, +1,200°C, +1,350°C and +1,400°C). Alloy materials for resistors retain their electrical properties when heated to +200°C... +600°C.

The heating of heat-resistant alloys provokes the formation of a protective film on the surface of the elements, which in turn prevents the oxidation of metals when in contact with oxygen. But if you exclude air access to the metal surface, you can significantly increase the life of the product. That is why in heating elements (tubular heating elements), precision alloy wire is placed in a metal body that is resistant to oxidation, and the space between them is filled with dielectric powder.