Composition: Hypoeutectic

Processing: Casting.

Etching: 10-30s immersion in 2% nital.

The microstructure consists of graphite flakes that were formed during solidification through a eutectic reaction. The pearlitic matrix is the result of the eutectoid transformation at lower temperatures (see diagram). MnS inclusions and the eutectic aggregate known as steadite are also revealed in the micrographs.

The precipitation of graphite is only possible when cast irons have a relatively high concentration of Si (2,5/2,7%) and are subjected to slow or moderate cooling through the eutectic transformation. 

Gray cast irons find applications for components that require good damping capacity and high compression strength. Tensile strength is much smaller due to the presence of flakes, whose sharp edges act as stress raisers promoting crack nucleation. It is possible to reduce the size of graphite flakes and, thus, improve the mechanical properties. This is carried out by the addition of innoculants before casting (FeSi, Al o Ca).

Fe-C diagram

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