①Gray cast iron. The carbon content is relatively high (2.7% ~ 4.0%), carbon mainly exists in the form of flake graphite, the fracture is gray, referred to as gray iron. Low melting point (1145 ～ 1250 ℃), small shrinkage during solidification, compressive strength and hardness close to carbon steel, good shock absorption. Due to the presence of flake graphite, the wear resistance is good. Casting performance and cutting are better. It is used to manufacture machine tool bed, cylinder, box and other structural parts. The brand name is followed by “HT” with two sets of numbers. For example: HT20-40 (the first number indicates the lowest tensile strength, the second set of numbers indicates the lowest bending strength).

②White cast iron. The content of carbon and silicon is low, carbon mainly exists in the form of cementite, and the fracture is silvery white. It shrinks greatly during solidification, and it is easy to produce shrinkage holes and cracks. High hardness and brittleness, can not bear impact load. It is mostly used as the blank of malleable cast iron and the production of wear-resistant parts.

③ Malleable cast iron. Obtained from annealing treatment of white cast iron, graphite is in floc distribution, referred to as tough iron. Its organizational performance is uniform, wear-resistant, and has good plasticity and toughness. Used to manufacture parts with complex shapes that can withstand strong dynamic loads.