These microstructural
features are affected by the solidification–cooling rate associated with the section size of the castings as well as
that of the alloying elements. Bainite and martensite are not found in as-cast structures because they are
formed by heat treatment. The matrix structure can be altered in subsequent heat treatment processing. However,
the amount and form of the graphite in ductile cast iron are determined during solidification and cannot
be altered by subsequent heat treatment. All of the mechanical properties of this class of materials are a result
of the graphite being substantially or wholly in the spheroidal nodular shape