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Physical properties of iron

Iron is a Group VIII element in the periodic table. Its physical properties are similar to those of nickel. The melting point of pure iron is 1535℃. Among non-refractory metals, although iron has the highest melting point and many good properties, it is difficult to clean and degas iron, so its application in lamp manufacturing is very limited except for lamp holders and lamps.

The evaporation rate and expansion coefficient of iron in vacuum are the same as those of nickel. However, the working temperature of iron cannot be too high because there are always various impurities in iron, which are easy to evaporate at high temperatures.

The resistivity and temperature coefficient of resistance of iron are higher than those of other non-refractory metals. The thermal conductivity of iron is relatively high. After heating iron to 600~700℃, its strength decreases more than nickel. The ductility of iron is lower than that of nickel, and the creep limit is not as high as that of nickel. Under long-term high temperature, the shape stability of iron parts is poor.

One of the outstanding properties of iron is that it has strong magnetism. Pure iron magnetizes and demagnetizes very quickly. At 768℃, the magnet will lose its magnetism. Therefore, this should be carefully considered when iron is degassed by high frequency heating and when it needs to maintain ferromagnetism at high temperatures.

Another characteristic of ordinary iron is its permeability to hydrogen, which can diffuse in an atomic state. At atmospheric pressure and a temperature of 850°C, every 100g of iron can absorb 0.26g of hydrogen. Therefore, parts made of steel generally cannot be annealed in hydrogen.

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