The furnace atmosphere has an effect on the performance and service life of heating alloys such as Nichrome alloys and FeCrAl alloys. NiWire Industries has a research on the following different gases.
1. Dry air and pure oxygen. Nichrome alloys and FeCrAl alloys have best oxidation resistance when they are used in dry air condition; also in pure oxygen atmosphere. The former is much better.
2. Gases contain sulphur. Usually some gases contain sulphur impurity, and some material and oil cause sulphur pollution when furnace is made. In this atmosphere, nichrome alloys have a worse performance than FeCrAl alloys. The surface of nichrome alloy heating elements will form a melting zone when used at high temperature and in gases contain sulphur. And sulphur will permeate into nichrome alloys through the melting zone. Finally austenite grain boundary will be occupied by sulphide.
3. Nitrogen. The service life of FeCrAl alloys will be much shorter when they are used in nitrogen than air. This is because Element chromium and aluminum have a strong affinity with nitrogen. Layer of oxidem will be destroyed to form oxide, besides aluminum will be separated from alloy and form nitride.
4. CO and CO2. When used in a carbon atmosphere, the layer of oxidem can protect the element from carbonization if the operation temperature is not high. The performation of both kinds of alloys will fall when the temperature goes higher. Because layer of oxidem is been destroyed and form carbide. If we continue to use, the element can be cracked or even burn out.
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