Nickel Chrome Resistance Alloys
Nickel Chrome (NiCr) alloys are high-resistance materials typically used in applications with maximum operating temperatures up to 1,250°C (2,280°F).
These Austenitic alloys are known for their higher mechanical strength at temperatures compared to Iron Chrome Aluminum (FeCrAl) alloys as well as their higher creep strength. Nickel Chrome alloys also remain more ductile when compared to Iron Chrome Aluminum alloys after extended periods at temperature. A dark Chromium Oxide (Cr2O3) is formed at high temperatures which is susceptible to spalling, or flaking, causing potential contamination depending on the application. This oxide does not have electrical insulation properties like the Aluminum Oxide (Al2O3) of Iron Chrome Aluminum alloys. Nickel Chrome alloys exhibit good corrosion resistance with exception to environments where sulfur is present.
Hyndman Industrial Products offers a variety of Nickel Chrome alloys and keeps the most common in inventory.
N4: Common Name: Chromel D, Nikrothal 40, Tophet D, Resistohm 40, Stablohm 610
Typical applications include night-storage heaters, convection heaters, heavy-duty rheostats and fan heaters. It is also used in heating cables and rope heaters in defrosting and de-icing elements, electric blankets and pads, car seats, baseboard heaters, floor heaters, resistors, etc. This Nickel-Chrome-Iron alloy has been widely used for furnace elements in the critical temperature range between 816° and 982°C in atmospheres where preferential oxidation of chromium takes place - the “Green Rot” range. N4 is also widely used as electric heating element material in domestic appliances and other electric heating equipment at operating temperatures up to 1100°C. It has good ductility after use, good corrosion resistance except in sulfur containing atmospheres and certain controlled atmospheres and excellent weldability.
N6: Common Name: Chromel C, Nikrothal 60, Tophet C, Resistohm 60, Alloy C, MWS-675, Stablohm 675
Typical applications include metal-sheathed tubular elements used in hot plates, grills, toaster ovens, storage heaters, etc. and as suspended coils in air heaters used in clothes dryers, fan heaters, hand dryers, etc. In addition to its use as an electrical heating element material, it is also ideally suited for "cold" resistors, rheostats, motor overload control devices, and other types of current-temperature control equipment because of its ability to withstand high overloads. This alloy has earned a reputation as the most suitable element for domestic appliances where consistent high quality is essential but where operating temperatures do not require the high heat resisting properties of the 80/20 Nickel Chrome alloy. The alloy has good corrosion resistance except in sulfur containing atmospheres and certain controlled atmospheres. The high electrical resistivity, relatively low TCR, and its ease of fabrication have made this alloy widely used in "edge-wound" power resistors.
N7: Common Name: Chromel 70/30, Nikrothal 70, Tophet 30, Resistohm 70, Stablohm 710
Used for corrosion resistant electric heating elements in industrial furnaces with reducing atmospheres. Highly resistant to "green rot" – a preferential intergranular oxidation of the chromium that is commonly experienced with other alloys under certain environmental conditions. Highly resistant to oxidation in air. Not recommend for use in MgO sheathed heating elements, or applications using nitrogen or carburizing atmospheres.
N8: Common Name: Chromel A, Nikrothal 80, Tophet A, Resistohm 80, Alloy A, MWS-650, Stablohm 650
Typical applications include flat irons, ironing machines, water heaters, plastic molding dies, soldering irons, metal sheathed tubular elements, cartridge elements, quartz tube heaters, etc. N8 has a low temperature coefficient of resistance and a low change in resistance during its service life that combine to assure faster heat-up times, more uniform operating temperatures, and a longer useful life. Its lack of reactivity with MgO refractories make it the most suitable alloy for enclosed heating elements, especially those operating in the higher temperature ranges. The oldest and most common electric heating alloy, N8 is long established as the world standard of quality among all metallic heating element materials. Its excellent mechanical stability minimizes variables in element design, assures even stretch in coiled form, and eliminates problems of shrinkage, growth, sag, or distortion in use.