Life of resistance alloys in controlled carbon-containing atmospheres

Conclusions

• 1. Iron-chromium-aluminum alloys have the longest life in controlled carbon-containing atmospheres. Their advantage over nickel-chromium alloys increases with an increase in carbon potential and operating temperature.

• 2. It is desirable to use alloys in an area in which the atmosphere possesses oxidizing properties in relation to them. Under otherwise equal conditions the resulting oxidizing properties of the atmosphere increase with a reduction in temperature and carbon potential. In the oxidizing area the oxide film protecting them from further interaction with the aggressive reactants of the atmosphere is maintained on the alloys.

• 3. Overheating and an uncontrolled increase in atmosphere carbon potential may lead to a breakdown in continuity of the protective oxide film and early failure of the element. This is responsible for the additional importance of reliable and accurate control of the temperature and atmosphere composition in electric furnaces with controlled carbon-containing atmospheres.

• 4. The areas of use of alloys in controlled carbon-containing atmospheres must be limited by the maximum allowable temperature and carbon potential, exceeding of which sharply reduces their service life as heating elements.

• 5. In service of the alloys in a controlled carbon-containing atmosphere under conditions close to critical it is desirable to heat them in advance in air to form a protective oxide film on the surface.