ABSTRACT
The requirement for a casing to deliberately fragment in service must be unique to the military. The high explosive filling is expected to cause the shell to burst in a reasonably predictable manner, giving an optimum number and size of fragments to act as omnidirectional secondary projectiles. Cast irons are Fe-C alloys with about 4%C by weight giving free carbon in the microstructure in the form of brittle graphite, resulting in low tensile strength and ductility. The optical microstructure of flake grey cast iron is seen in Plate 52 – graphite flakes in a ferrite matrix. The optical microstructure of spheroidal graphite cast iron is seen in Plate 53 – graphite nodules in a ferrite matrix. Most steels have much higher strength and ductility than cast iron because their lower %C means the carbon is present as comparatively finely divided iron carbide Iron carbide.
