Cast iron composition
Cast iron is an alloy of iron and carbon (quantitywhich is more than 2.14%), is characterized by eutectic formations. Carbon in cast iron is in the form of graphite and cementite. Depending on the forms of graphite, and the amount of cementite cast iron is divided into: white and gray, malleable and high-strength cast iron. Chem. The composition of cast iron contains permanent impurities (Si, Mn, PS, P), and in rare cases alloying elements like (Cr, Ni, V, Al, etc.) are also present. Cast iron is usually brittle. The large spread of cast iron in mechanical engineering was facilitated by the presence of good foundries, as well as strength and hardness. World production of pig iron before the crisis of 2008 amounted to more than 953 million tons (in particular, China smelted 477 million tons).
Chemical composition of cast iron and its types
White and gray cast iron types are distinguished by colorfracture, which is determined by the structure of carbon in cast iron as iron carbide or free graphite, high-strength cast iron with nodular graphite, cast iron with vermicular graphite are called forging. Carbon in white cast iron is in the form of cementite, and in gray cast iron, it is in the form of graphite.
Composition of cast iron white
In white cast iron, all carbon present comes in a state of cementite. The structure of white cast iron includes - perlite, ledeburite, also cementite. Through a light cast, the cast iron was called white.
The composition of gray iron and its structure
Gray cast iron is a kind of cast iron that does not contain ledeburite, in it all carbon (or part of carbon) is in the form of graphite. The name came from the gray color of the fracture surface.
Belongs to white cast iron, to the maintypes of cast iron. In the composition of gray cast iron, except iron and carbon (2.5 ... 4.5%), silicon is about (0.8 ... 4.5%), as well as manganese (0.1 ... 1, 2%), and phosphorus (0, 02 ... 0.3%) with sulfur (0.02 ... 0.15%). The tensile strength of gray cast iron is 100 ... 350 MPa, compression is 450 ... 1400 MPa, Brinell hardness is 143 ... 289 HB.
The main characteristic of gray cast iron is lowtear resistance, sufficiently low impact strength. Therefore, the smaller the graphite plates are and the stronger the plates are insulated from one to the next, the higher the strength of cast iron with the same metal base. This structure is obtained by modifying, the process of introducing small amounts of substances into the liquid metal alloy, which are called modifiers (ferrosilicon and silicocalcium)
Ductile cast iron, the process of obtaining
Ductile iron is obtained as a result of a longannealing of white cast iron, after this process graphite is formed flocculent. The metallic base of malleable cast iron contains: ferrite and less often perlite.
Structure of high-strength cast iron
In its structure, high-strength cast iron hasGlobular graphite, it is obtained in the process of crystallization of the material. Spherical graphite very weakens the metal base as much as a tabular, not a stress concentrator.
Structural characteristics of half-cast iron
Part of the carbon in the half-cast iron (more than 0.8%) is in the types of cementite. The main structural components of this cast iron are pearlite, ledeburite and flat graphite.
Classification of cast iron
From the chemical composition of cast iron and carbon content, graycast iron is called pre-eutectic has (2.14-4.3% carbon), and eutectic has (4.3%) hypereutectic has (4.3-6.67%). The composition of the alloy strongly affects the structure of the final material.
In industry, different types of cast iron have such markings:
- cast iron-P1, P2;
- cast iron for castings use-PL1, PL2,
- processing phosphorous type of cast iron-PF1, PF2, PF3,
- processing high-quality view of cast iron-ПВК1, ПВК2, ПВК3;
- cast iron having lamellar graphite-SCH (digits going after the letters "> MF", denote the value of the temporary resistance of the rupture (VKG / mm);
Antifriction cast iron types:
- antifriction gray-ASF,
- antifriction high-strength type-AFB,
- antifrictional malleable view-ACHK;
Cast iron, which has a globular graphite for castings - HF (figures following the letters "HF" means the temporary resistance of the rupture VKG / mm;
At the beginning of the 16th century, cast iron was also smeltedRussian Empire. Melting of pig iron grew very rapidly and during the reign of Peter 1, Russia was the leader in the smelting of metal in Europe. Over time, foundries began to separate from blast furnaces, which gave impetus to the development of independent cast-iron foundries. At the beginning of the 19th century, factories began to produce malleable cast iron, and at the end of the 20th century they began to manufacture alloyed cast iron.