Grey Iron Casting

In grey cast iron the free graphite is in the form of flakes. The matrix may be ferritic for the lower strengths to pearlitic for higher strength.

Structure
The structure of grey irons often display three phases, ferrite, pearlite or martensite. The carbon content of the matrix rarely exceed 1%. Metallographic sections usually reveal graphite as flakes, however it is actually present in rose-like structures. The distribution of these structures can strongly influence the properties of the metal. The best grey irons have a steel matrix with graphite flakes of varying size and uniform distribution.
The matrix structures also influence properties as follows:
•         Ferrite matrix – low strength
•         Pearlite matrix – higher strength
•         Martensite matrix – high strength, higher hardness, when high carbon grey irons are quench hardened.

Applications
Classic applications for grey cast iron are engine cylinder heads and blocks utilising the thin and complex cast sections for water cooling passages and the damping characteristics for quietness.
Gear boxes and gears are made in grey cast iron for quietness and the wear properties.
Machine tool slideways use the wear characteristics.
General engineering castings benefit from the ease of casting, the comparatively simple pattern equipment and the shorter lead times to produce castings.