Economically alloyed alloys
From the alloys of nickel and chromium with high electrical resistance — Х20Н80 (nichrome) for many years, traditionally produced heating elements for household appliances and industrial installations. But due to the high price of these alloys and the unsatisfactory resistance to corrosion in steams of sulfur and sulfur oxides, carburizing, oxidizing gases, so often used in production, they were pressed in the world market by fechrali.
Disadvantages of nichromes
From the alloys of nickel and chromium with high electrical resistance — nichromes (they can contain up to 80% Ni) for many years, traditionally produced heating elements for household appliances and industrial installations. But due to the high price of these alloys and the unsatisfactory resistance to corrosion in sulfur and sulfur oxides, carburizing, oxidizing gases, so often used in production, they were pressed in the world market by fechrales (Fe-Cr-Al) and economically nickel-doped ferronichromes (Fe-Ni-Cr). The share of the latter in the consumption sector of special alloys of heating abroad reached almost 85% and continues to grow.
Why the domestic market is focused on nichrome
There are several reasons. One of the main things is that the domestic obsolete technologies give the properties of chromium-aluminum alloys that are unstable from batch to batch. Domestic fekhrali are prone to intercrystalline corrosion destruction, high temperature embrittlement, rapid manifestation of creep characteristics and sagging during strong heating. Therefore, consumers often prefer expensive nickel alloys, such as: Kh20N80 and Kh15N60 with better characteristics than domestic fechrals.
Advantages of high-quality felholes
Negative experience with the use of Russian fechrals, makes consumers wary of high-quality foreign analogues. And, meanwhile, modern technologies guarantee the homogeneity of the fecal structure, the continuity of the protective oxide layer and its «adhesion» to the surface due to precision microalloying by elements such as Al, Mn, and Si. Zr, etc. Reducing the carbon content below 0.03% gives a high plasticity, eliminates the tendency to intercrystalline high-temperature corrosion, increases the creep limit and resistance to oxidation, the action of sulfur and its oxides, carburization with significant heating.
The stability of fechrals to oxidation in aggressive industrial environments gives a chemically inert, dense surface protective oxide layer based on Al 2 O 3. Fehrali is resistant to organic acids and caustic alkalis, to chloride pitting and crevice corrosion, chloride corrosion cracking. In a CO-containing atmosphere, nickel alloys at 800−950 ° C lose their surface protective oxide layer due to simultaneous oxidation and carburization and are covered with so-called «green rot». Foreign fechrals are more heat resistant and durable than nichrome and ferronichromes, and also have a more stable temperature coefficient of electrical resistance, which allows to maintain the heating temperature precisely. In some cases it is advisable to use preliminary oxidation of fechrals.
High-quality and relatively cheap foreign fechrales have an extended service life and high manufacturing technology of heating elements. So, fechrali (especially with the addition of yttrium) are used not only for embedded and wound spirals on the matrix bases of household electrical appliances and industrial equipment, but also in suspended and tension type heaters (hair dryers, thermal ventilators, heat guns, etc.).