Ductile iron: is the general term for alloys composed of iron, carbon and silicon. Cast iron is mainly composed of iron, carbon and silicon. In terms of classification, according to production method and organization performance, it is divided into (1) "Gray Cast Iron" . (2) Also known as metamorphic cast iron. Its strength, plasticity and toughness are better than general gray cast iron and the structure is more uniform. It is used to manufacture large-scale castings with high requirements on mechanical properties and large changes in cross-sectional dimensions . (3) Tough cast iron, made of white cast iron with a certain composition after graphitization and annealing. (4) Ductile iron is referred to as ductile iron.