Casting iron

Iron-carbon alloys containing more than 2% carbon. Industrial cast iron generally contains 2% to 4% carbon. Carbon exists in cast iron mostly in the form of graphite, and sometimes in the form of cementite. In addition to carbon, cast iron also contains 1% to 3% silicon, as well as manganese, phosphorus, sulfur and other elements. Alloy cast iron also contains nickel, chromium, molybdenum, aluminum, copper, boron, vanadium and other elements. Carbon and silicon are the main elements that affect the microstructure and properties of cast iron. Cast iron can be divided into:
① Gray cast iron. The carbon content is high (2.7% ~ 4.0%), the 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. Used to manufacture machine tool bed, cylinder, box and other structural parts.
② White cast iron. The content of carbon and silicon is low, the carbon mainly exists in the form of cementite, and the fracture is silver-white. Shrinkage during solidification is large, which is easy to produce shrinkage holes and cracks. High hardness, brittleness, can not withstand the impact load. It is often used as a blank for malleable cast iron and to make wear-resistant parts.
③ malleable cast iron. Obtained from white cast iron after annealing treatment, the graphite is distributed in clumps and flocculation, referred to as tough iron. It has uniform microstructure, abrasion resistance, good plasticity and toughness. It is used to manufacture parts with complex shapes that can withstand strong dynamic loads.
④ Nodular iron. Gray cast iron molten iron is obtained by spheroidizing treatment, and the precipitated graphite is spherical, referred to as ductile iron. Compared with ordinary gray cast iron, it has higher strength, better toughness and plasticity. Used in the manufacture of internal combustion engines, auto parts and agricultural machinery.
⑤ vermicular graphite cast iron. The graphite precipitated from gray cast iron molten iron was worm-like. The mechanical properties are similar to nodular cast iron, and the casting properties are between gray cast iron and nodular cast iron. Used to make parts for cars.
⑥ Alloy cast iron. Ordinary cast iron is obtained by adding appropriate alloying elements (such as silicon, manganese, phosphorus, nickel, chromium, molybdenum, copper, aluminum, boron, vanadium, tin, etc.). Alloying elements make the matrix structure of cast iron change, so that it has the corresponding heat resistance, wear resistance, corrosion resistance, low temperature resistance or no magnetic properties. Used in the manufacture of mining, chemical machinery and instruments, instruments and other parts.


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1. Divide by fracture color
(1) Most or all of the carbon in this cast iron is in the form of free state flake graphite, its fracture is dark gray, has a certain mechanical properties and good cutting performance, widely used in industry
(2) White cast iron White cast iron is an iron-carbon alloy with no or almost no graphite in the organization, its fracture is white and bright, hard and brittle, can not be cut, and is rarely used directly in the industry to make mechanical parts. Because of its high surface hardness and wear resistance, it is also known as chilled cast iron or chilled cast iron
(3) pitted cast iron pitted cast iron is a kind of cast iron between white cast iron and gray cast iron, its fracture is gray and white dotted, poor performance, rarely used
2. By chemical composition
(1) Ordinary cast iron refers to cast iron that does not contain any alloying elements, such as gray cast iron, malleable cast iron, ductile cast iron, etc
(2) Alloy cast iron is a high-grade cast iron prepared by adding some alloying elements to ordinary cast iron to improve some special properties. Such as a variety of corrosion resistance, heat resistance, wear resistance of the special properties of cast iron
3. According to the production method and organizational performance
(1) Ordinary gray cast iron see "gray cast iron"
(2) Inoculation cast iron This is on the basis of gray cast iron, the use of "metamorphic treatment", also known as metamorphic cast iron. Its strength, plasticity and toughness are much better than the general gray cast iron, and the organization is more uniform. It is mainly used in the manufacture of large castings with high mechanical properties and large cross-section size changes
(3) Malleable cast iron Malleable cast iron is made of a certain composition of white cast iron by graphitization annealing, has higher toughness than gray cast iron, also known as ductile cast iron. It cannot be forged and is commonly used to make castings that withstand impact loads
(4) nodular iron referred to as ductile iron. It is obtained by adding a certain amount of spheroidizing agent and inking agent to the liquid iron before casting to promote the crystallization of spheroidal graphite. Compared with steel, in addition to the plasticity, toughness is slightly lower, other properties are close, is both the advantages of steel and cast iron excellent materials, widely used in mechanical engineering
(5) Special performance cast iron This is a kind of cast iron with certain characteristics, according to the different uses, can be divided into wear-resistant cast iron, heat-resistant cast iron, corrosion resistant cast iron and so on. Most of them belong to alloy cast iron, which is widely used in mechanical manufacturing.