Growth

At high temperatures, the cementite contained in pearlite breaks down to graphite and austenite. This implies a considerable increase in volume. Moreover, internal oxidation is possible which even increases the volume since graphite and austenite or ferrite have a larger volume than cementite, and iron oxide has a larger volume than iron. This is particularly applicable to flake graphite cast iron.

The volume consistency of nodular graphite cast iron mainly depends on the amount and stability of pearlite. Ferrite types are practically resistant to growth. The carbon available in the pearlite or as free cementite and which is decomposed to form graphite and ferrite may result in a linear growth of 0.4 to 0.5 %. This corresponds to a volume increase of 1.2 to 1.5 %.

Pearlite compostation already starts at temperatures of around 450 °C and increases with increasing temperatures. At the same time, the mechanical properties change so that components for which constant mechanical properties at application temperatures of > 450 °C over a longer period of time are required may only be made of ferritenodular graphite cast iron.

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