Ductile iron refers to cast iron in which the graphite is spherical after the molten iron is treated with a spheroidizing agent. That is why the ductile cast iron is also called spheroidal graphite cast iron or nodular cast iron. Inside the ductile cast iron by electron microsope, the shape of spheroidal graphite is approximately spherical, and its interior is radial shape, and it has obvious polarization effect. The spheroidization rate refers to the percentage of the total number of spherical graphite in a certain range to the total number of graphite. The spheroidization rate is an index to measure the spheroidization grade of nodular cast iron, and it is an important standard in ductile cast iron castings.