Ductile iron: is a general term for alloys composed of iron, carbon and silicon. Cast iron is mainly composed of iron, carbon and silicon. Classification, according to production methods and organizational performance points (1) "gray cast iron" . (2) Also known as metamorphic cast iron. Its strength, plasticity and toughness are better than ordinary gray cast iron and the structure is more uniform. It is used to manufacture large castings with high mechanical performance requirements and large changes in cross-sectional dimensions . (3) Toughened cast iron, made of white cast iron with certain composition through graphitization annealing. (4) Ductile iron is referred to as ductile iron.