| Alloy | resistivity | Elongation | Density | max. temperature | melting point |
| 電阻率 (Ωmm2/m) | 延伸率(%) | 密度(g/cm3) | 最高使用溫度(℃) | 熔點(℃) | |
| NiCr80 | 1.09 | > 20 | 8.3 | 1200 | 1400 |
| Ocr25Al5 | 1.42 | > 12 | 7.1 | 1250 | 1500 |
| Ocr23Al5 | 1.35 | > 12 | 7.25 | 1250 | 1500 |
| CN49 / CuNi44 | 0.49 | >25 | 8.9 | 400 | 1280 |
| CuNi30 | 0.35 | >25 | 8.9 | 350 | 1170 |
| CuNi15 | 0.15 | >25 | 8.9 | 220 | 1100 |
| CuNi10 | 0.1 | >25 | 8.9 | 200 | 1100 |
| CuNi5 | 0.05 | >25 | 8.9 | 150 | 1080 |
Quality Characteristic
To become a significant electric heating element, a metal or alloys should have the following:
1. Good high electric resistivity to keep small cross-sectional area
2. High strength and ductility at the working temperatures
3. Low temperature coefficient of electric resistance to prevent changes in resistance at the working temperature significantly from that attained to room temperature.
4. Excellent resistance to oxidation in air while moderate procedures
5. Suitable working and potential for being formed into the required shape.
One of the characteristics of electrothermal alloy materials that are different from ordinary conductive materials is that they have certain requirements for the resistivity of materials. Ordinary conductive materials hope that the resistivity is as small as possible, while the electrothermal alloy material must have sufficient resistivity to ensure that the electrothermal element has a high electrothermal conversion rate, compact structure, and stable power transmission. Nichrome wire has a higher resistivity than copper wire.
(1) High resistivity value: The electrothermal alloy material should first have a relatively high resistivity. The electric heating element made of high resistivity material has high electrothermal conversion efficiency; the volume of the electric heating element is small; alloy material is saved; high power and rapid heating can be realized. It is especially important when designing an electric heating furnace with high temperature, high power, and small size. When designing heating elements, in principle, alloy materials with high resistivity should be used for high temperature elements, and alloy materials with lower resistivity should be used for medium and low temperature elements.
(2) Resistivity remains stable during use: the resistivity of the heating element should remain stable during use. The smaller the change in resistivity, the smaller the change in the resistance of the element, and the smaller the change in the heating electric power, thus ensuring a good and stable heating quality. Due to the change of chemical composition and the precipitation of compounds along the grain boundary or within the grain of the electrothermal alloy at high temperature, the resistivity will change. The metallographic structure of nickel-chromium and nickel-chromium-iron alloys is relatively stable at high temperatures, so the resistivity is stable during long-term use. On the contrary, the stability of iron-chromium-aluminum alloys is relatively poor, mainly because the amount of aluminum in the alloy decreases sequentially, resulting in changes in resistivity.
(3) The uniformity of resistivity is better: the uniformity of resistivity means that the resistivity or resistance value per meter of each meter and batch of electrothermal alloy wire or strip should be uniform, and the smaller the fluctuation range, the better. The uniformity of resistivity is related to many factors such as alloy smelting, billet casting, heat treatment, and single weight of wire rod. The resistivity uniformity of nickel-chromium and nickel-chromium-iron alloys is better than that of iron-chromium-aluminum alloys. The aluminum in the latter is prone to segregation during smelting and ingot casting (the phenomenon that the components in the alloy are unevenly distributed during crystallization is called segregation), leading to a decrease in the homogeneity of the alloy. Uniformity of resistivity is especially important for filaments and thin strips. Because they are mostly used to produce heating elements for household electrical appliances with large batches, if the resistivity uniformity is poor, the power of each element will be different.
(4) The change value of resistivity with temperature is small: there is a linear relationship between resistivity and temperature, and this relationship can be expressed by the temperature coefficient of resistance. The smaller the absolute value of the temperature coefficient of resistance of the ideal electrothermal alloy material, the better. The smaller the temperature coefficient of resistance, the smaller the resistance change during the heating process, and the smaller the resistance fluctuation value of the heating element, which can realize stable heating.