How to use silicon carbide

Metallurgical grade silicon carbide has a purity between 88% and 90%. When calculating carburization and siliconization, the amount of impurities must first be deducted. According to the molecular formula of silicon carbide, it is easy to conclude:

Carburizing:?C=C/(C+Si)=12/(12+28)=30% ??????????????????????

Increase silicon: Si=Si/(C+Si)=28/(12+28)=70% ?????????????????

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The amount of silicon carbide added is usually only 0.8%~1.0% of molten iron. The method of adding silicon carbide is:

When smelting molten iron in an electric furnace, when 1/3 of the charge is melted in the crucible, add it to the middle of the crucible, try not to touch the furnace wall, and then continue to add the charge for smelting.

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To smelt molten iron in a cupola furnace, silicon carbide with a particle size of 1~5 mm can be mixed with an appropriate amount of cement or other binders, and water can be added to form a lump. After being dried in the hot sun, it can be put into the furnace for use according to the batch ratio.

The application of thin-walled gray cast iron, ductile iron and vermicular graphite castings, thick-walled ductile iron castings and Auberge ductile iron castings puts forward higher requirements for the metallurgical quality of cast iron. The inoculation pretreatment of silicon carbide has a good effect on improving the metallurgical quality of cast iron.

After the pretreatment agent is added to the molten iron, two effects can be observed: one is that the carbon equivalent is increased; the other is that the metallurgical conditions of the molten iron are changed, which strengthens the reduceability. In 1978, B.C. Godsell of the United Kingdom published the results of his research on the pretreatment of ductile iron. Since then, experimental research on the pretreatment process has continued uninterrupted, and now this process has become relatively mature. Research results show that for gray cast iron, metallurgical silicon carbide with a SiC content of 85% to 90% is most effective; for ductile iron, crystalline silicon carbide with a SiC content of 97% to 98% is most effective.

For gray cast iron, silicon carbide inoculation pretreatment can reduce the degree of subcooling and reduce the whitening tendency; Increase the graphite core, promote the formation of A-type graphite, reduce or prevent the production of B-type, E-type and D-type graphite, increase the number of eutectic clusters, and obtain fine flake graphite; For ductile iron, silicon carbide inoculation pretreatment promotes an increase in the number of graphite nodules in the cast iron, increases the spheroidization rate, and improves the roundness of the graphite nodules. The use of silicon carbide can strengthen the deoxidation and reduction of iron oxide, make the cast iron structure dense and increase the smoothness of the cutting surface. The use of silicon carbide can extend the life of the furnace wall without increasing the aluminum and sulfur content of the molten iron.

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