The micro structure of lamella graphite cast iron
Spheroidal graphite cast iron micro structure
SPHEROID CAST IRON IS A QUITE RESISTANT MATERIAL COMPARED TO GREY CAST IRON:
Spheroidal cast iron has structure made of SPHEROID graphite dispersed in a matrix similar to that of steel. The sole micro-structural difference from gray cast iron is the shape of graphite.
Spheroidal cast iron is a material that represents the major benefits of grey cast iron (such as low melting grade, good fluid and casting, perfect processing facility and a good cutting strength) as well as the advantages of steel in terms of engineering (high resistance, stability, flexibility, hot processing capability and hardening). In other words, spheroidal cast irons are special materials that due to their mechanical features, are identical with cast steel with cast iron characteristics in terms of manufacturing method.
Although both grey cast iron and spheroidal cast iron are the same based on chemical composition (except for sulfur and manganese), stiffening of both cast irons occurs highly different. Such difference also leads to the change in the material’s mechanical features.
The sole micro-structural difference between the spheroid cast iron and grey cast iron is the shape of the graphites. The sharp edges of the grey cast iron graphites lead to increased tension and cause a NOTCH EFFECT to some extent. This is the origin of any possible cracks caused by material load.
Also the matrix interruption that is caused by the graphite results in weak and crisp metals. The draw resistance of the metal matrix is around 60-100Kg/mm² while that of grey cast iron is 18 – 30kg/mm² dir. The conversion of the sharp edged graphite of the grey cast iron to a similar structure as the spheroid one will ensure less deformation of the matrix stability, thus, spheroid graphites which do not lead to the notch effect will increase the material resistance.
The draw resistance of spheroid cast iron is slightly higher than that of grey cast iron, which results in enhanced material resistance.
Spheroid material’s high draw resistance compared to grey cast iron ensures a weight effectiveness up to 100% for Manholes and Rainwater gully gratings