Tellurium’s effects on properties of gray cast iron

Tellurium coating is often used to solve the leakage problem of cylinder blocks and heads. However, it has been revealed by investigation that the tellurium could influence the graphite morphology and matrix structure of cast irons and caused decrease of mechanical properties of cast irons. When adding relatively less amount of tellurium, Te restricts the growth of graphite and causes the graphite become finer, shorter, curved, causes some lump-shaped graphite appearing and increases the graphite count that results in increasing of ferrite content. When adding relatively big amount of tellurium, Te and MnS would combine to form paragenous compound which is accumulating at the fronts of eutectic cells and causes composition super-cooling of the iron melt. As a result, the iron melt would solidify according to the quasi-stable system and lead to formation of the white structure. Therefore, the quality of the tellurium coating must be strictly controlled in the production process.

The reason is that tellurium is a strong anti-graphitization element, which can effectively promote the formation of white hole structure in gray cast iron. Its exact mechanism is still under discussion at present, but it is generally believed that tellurium has a low melting point and can be melted in molten iron, which affects the crystallization and solidification process of molten iron.

The effect of tellurium on the properties of gray cast iron is mainly realized through the effect on the matrix structure and graphite morphology of cast iron. Because tellurium has a great influence on the performance of gray cast iron which is necessary to strictly control the performance of cold-shock coating in casting production, so that the coating can have the effect of "in place" cold-shock and avoid the thin coating being washed into the casting by molten iron.

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