The role of electric heating chromium:

The role of electric heating chromium:

Chromium is a key element to improve the high temperature oxidation resistance of nickel-chromium and nickel-chromium-iron electric heating alloys. The protective oxide film formed by the alloy at high temperature is mainly composed of Cr2O3. The oxide film mainly made of Cr2O3 is denser and has strong adaptability, which can ensure long-term use of the alloy at high temperatures. The oxidation rate of the alloy decreases as the chromium content increases. The relationship between chromium content, temperature and oxidation rate in Fe-Cr system is shown in Figure 3-2.

In order to maintain the good oxidation resistance of the electric heating alloy at high temperature, it is required that the oxidation weight gain of the alloy at this temperature is not more than 2.0*10-2g.cm-2.h-1. According to this value, nickel-chromium and nickel-chromium-iron electric heating alloys containing 15%~18%, 19%~23% and 28%~31% of Cr, the highest oxidation resistance temperature is correspondingly: 900~950℃, 1000~1100℃ And 1000~1200℃.

After high temperature oxidation, silicon forms SiO2, which is distributed at the interface between the oxide film and the base metal. SiO2 can hinder oxygen infiltration and reduce the oxidation rate of the alloy.

In nickel-chromium and nickel-chromium-iron electric heating alloys, the elements that improve the oxidation resistance are chromium and silicon. The nickel, iron, manganese, carbon, etc. in the alloy have an unfavorable effect on the high-temperature oxidation resistance. The trace elements lanthanum, cerium, Rare earth elements such as yttrium can improve the oxidation resistance of the alloy.

When the internal oxidation of the alloy progresses to a certain limit, the oxide film begins to crack. The appearance of cracks causes a large amount of oxygen to enter the inside of the alloy, and a large amount of iron, aluminum, silicon, chromium, etc. are oxidized, which promotes a rapid increase in the oxidation rate. At the same time, a large number of cracks begin to appear in the oxide film, which eventually leads to damage.

In short, the oxidation process of the electric heating alloy reflects the destruction process of the electric heating element. How to establish a protective oxide film and develop the oxidation stability stage of the alloy is of great significance to extending the service life of the electrothermal alloy.

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