High-strength cast iron - not the only representative special alloy
Fuses it in blast furnaces from iron ore. The result is an alloy of iron with carbon and some other components, such as chromium or nickel. The alloy is highly fragile. Carbon in cast iron is present in the form of graphite or cementite.
The formation of graphite occurs during its separation from the liquid alloy or as a result of the decomposition of cementite. Its presence in the alloy increases the wear resistance of the metal. It perfectly suits tooling, during which a clean surface is formed.
Cast iron is mainly used only as a constituent of various alloys. High foundry qualities of this metal contributed to its wide application in industry. Fused in blast furnaces, it is divided according to its purpose into: remanufactured, foundry and special( ferroalloy) types. The first two of them are further used in the production of steel.
Foundry, whose production accounts for about 20% of all produced cast iron, are supplied to the machine building plants for the production of cast billets. Among the special alloys are heat-resistant, antifriction, non-magnetic, wear-resistant and heat-resistant cast iron. Let's consider each of them in more detail in the next section.
Heat-resistant cast iron - a bright representative of special alloys
Heat-resistant cast iron is a type of gray high-strength alloy, alloyed with silicon or chromium. This type of metal is resistant to high temperatures( up to 700-800 ° C).Also, high austenitic alloyed cast iron, which includes globular graphite, also have high heat resistance.
They are used in the manufacture of parts of various devices for the chemical industry, as well as turbochargers, which are operated at temperatures up to 700 ° C.
Heat-resistant varieties refer to austenitic with nodular graphite ЧН19ХЗШ.To improve their technological qualities, these alloys are annealed in heating furnaces with subsequent tempering. As a result of this process, carbides are formed in the metal structure in the form of round inclusions. They are used for the manufacture of parts of diesel engines, various compressor equipment, etc.
Other special cast iron
Cast iron antifriction belongs to gray high-strength cast iron of special grades. These materials are characterized by a low coefficient of friction, which directly depends on the quantitative ratio of ferrite and perlite in it, as well as on the volume and shape of graphite. Due to their metal base, pearlitic alloys are distinguished by their high wear resistance.
Wear-resistant cast iron is melted using alloying additives such as nickel, chromium, molybdenum. The finished material is subsequently subjected to heat treatment, which leads to an increase in the strength and wear resistance of the parts. Also, to improve the performance of a doped alloy, surface hardening by high-frequency currents is used.
Modified cast iron is produced by adding special modifiers to the molten metal. Some of them, for example, magnesium or yttrium at a certain concentration cause the release of graphite, which promotes the formation of a high-strength material with nodular graphite.
All kinds of special alloys are widely used in various fields of engineering, especially when the metal, apart from its high strength, must have certain specific qualities.
