Alloys of nickel and chromium with high electrical resistance - X20H80 (nichromes) for many years traditionally produced heating elements for household appliances and industrial installations. But because of the high price of these alloys and unsatisfactory resistance to corrosion in sulfur vapor and sulfur oxides, carburizing, oxidizing gases, so often used in manufacturing, they were superseded by ferrules in the world market.

Disadvantages of Nichromes

Alloys of nickel and chromium with high electrical resistance - nichromes (they can contain up to 80% Ni) have for many years been traditionally used to produce heating elements for household appliances and industrial plants. But due to the high price of these alloys and their unsatisfactory resistance to corrosion in sulfur vapor and sulfur oxides, carburizing, oxidizing gases so often used in production, they have been overtaken on the world market by Fe-Cr-Al and nickel-doped ferronichromes (Fe-Ni-Cr). The share of the latter in the consumption of special heating alloys abroad reached almost 85% and keeps growing.

Why does the domestic market focus on nichromes?

There are several reasons. One of the main reasons is that the domestic obsolete technology gives unstable properties of chrome-aluminum alloys from batch to batch. Domestic ferrules are prone to intercrystalline corrosion failure, high-temperature embrittlement, rapid manifestation of creep and sagging when heavily heated. That is why consumers often prefer expensive nickel alloys, such as X20H80 and X15H60, which have better characteristics than domestic fehrals.

Advantages of high quality ferrals

Negative experience in the use of Russian fechrals makes consumers cautious about high quality foreign analogues. However, modern technologies guarantee the homogeneous structure of ferrules, the continuity of the protective oxide layer and its "sticking" to the surface due to the precise micro alloying with such elements as Al, Mn, Si, Zr and others. Zr, etc. Reduction of carbon content below 0.03% gives high ductility, eliminates susceptibility to intergranular high-temperature corrosion, increases the creep limit and resistance to oxidation, the action of sulfur and its oxides, carburizing at significant heating.

Fechrals resistance to oxidation in aggressive industrial environments is given by chemically inert, dense surface protective oxide layer based on _Al203. Fehrals are more resistant to organic acids and caustic alkalis, chloride pitting and crevice corrosion, chloride corrosion cracking. In CO-containing atmospheres nickel alloys at 800-950°С due to simultaneous oxidation and carburizing lose the surface protective oxide layer and are covered with the so-called "green rot". Foreign ferrules are more heat-resistant and durable than nichrome and ferro-nichrome, and they also have a more stable temperature coefficient of electrical resistance, which allows to precisely maintain the heating temperature. In some cases it is reasonable to use pre-oxidation of fechrals.

High-quality and relatively cheap foreign fechrals have an increased service life and high technological efficiency of production of heating elements. Thus, fechrals (especially with yttrium additives) are used not only for built-in and wound spirals on matrix bases of household appliances and industrial equipment, but also in heaters of suspended and tension type (hair dryers, thermal fans, heat guns, etc .).