Ductile iron is mainly composed of iron, carbon and silicon alloy composition in general. In these alloys, the carbon content exceeds the eutectic temperature can be retained austenite amount in solid solution. Cast iron consists of iron, carbon and silicon alloy composition in general. In these alloys, the carbon content exceeds the eutectic temperature can be retained austenite amount in solid solution.

Carbon content of more than 2% of the iron-carbon alloy. Industrial carbon content of cast iron is generally 2% to 4%. More carbon in cast iron exists in the form of graphite, and sometimes the form of cementite exist. In addition to carbon, the iron also contains 1% to 3% silicon and manganese, phosphorus, sulfur and other elements. Alloy cast iron also contains nickel, chromium, molybdenum, aluminum, copper, boron, vanadium and other elements. Carbon, silicon is the impact of the main elements of microstructure and properties of cast iron. Cast iron can be divided into ① gray cast iron. Higher carbon content (2.7% to 4.0%), carbon exists mainly in the form of flake graphite, the fracture was gray, referred to as gray iron. Low melting point (1145 ~ 1250 ℃), small amount of shrinkage during solidification, compressive strength and hardness close to the carbon steel, good shock absorption. For the manufacture of machine bed, cylinder, box and other structural parts. ② white cast iron. Carbon, silicon content is low, carbon exists mainly in the form of cementite, the fracture was silver. Solidification shrinkage is large, easy to produce shrinkage cracks. High hardness, brittleness, can not withstand the impact load. More as blank and production of wear-resistant parts malleable iron. ③ malleable iron. After annealing white cast iron by the obtained graphite was flocculent distribution, referred to as ductile iron. Its homogeneous properties, wear resistance, good ductility and toughness. For the manufacture of complex shape to withstand a dynamic load of parts. ④ ductile iron. The gray cast iron after treatment to get the ball, spherical graphite precipitation, referred to as ductile iron. It has high strength, good toughness and ductility than ordinary gray cast iron. For the manufacture of internal combustion engines, auto parts and farm machinery. ⑤ compacted graphite iron. The gray cast iron after treatment creep obtain precipitated graphite vermiform. Mechanical properties of ductile iron similar between gray cast iron and ductile iron casting performance between. For the manufacture of automotive parts. ⑥ alloy cast iron. Ordinary cast iron by adding appropriate amount of alloying elements (such as silicon, manganese, phosphorus, nickel, chromium, molybdenum, copper, aluminum, boron, vanadium, tin, etc.) to obtain. Alloying elements iron matrix structure changes, so as to have the appropriate heat, wear and corrosion resistance, low or non-magnetic properties. For the manufacture of mining, chemical machinery and equipment, instruments and other components.