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
The strength of a grey cast iron varies with the section size of the
casting due to solidification effects: This is referred to as
Also, the strength in compression is three to four times the tensile
strength because of the planes of weakness created by the graphite
flakes. The material tends to be brittle compared to steel, but is
extremely stiff and deflects little before fracture. This imparts
the characteristic damping qualities of grey cast iron.
The graphite flakes also have a lubricating effect giving the
material advantages in sliding wear applications. Grey cast iron has
better casting characteristics than steel allowing finer detail and
complex shapes. It also machines more easily and quickly. A
disadvantage is that it cannot be readily welded.
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