Nodular cast iron steel pipes are essentially ductile iron pipes, which have the essence of iron and the properties of steel, hence their name. Graphite in ductile iron pipes exists in a spherical form, with a general size of 6-7 grades. In terms of quality, the spheroidization level of cast iron pipes is required to be controlled at 1-3 levels, with a spheroidization rate of ≥ 80%. Therefore, the mechanical properties of the material itself have been improved, possessing the essence of iron and the properties of steel. After annealing, the microstructure of ductile iron pipes is ferrite with a small amount of pearlite, which has good mechanical properties, hence it is also called cast iron steel pipes.