Alloy Steel

alloy steel [¦a‚lȯi ¦stēl]

(metallurgy)

A steel whose distinctive properties are due to the presence of one or more elements other than carbon.

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alloy steel

Steel containing one or more alloying elements other than carbon, such as chromium, molybdenum, or nickel, which have been added (in an amount exceeding a specified minimum) to impart particular physical, mechanical, or chemical properties.

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Alloy Steel 

steel that contains—in addition to iron, carbon, and unavoidable impurities—alloying elements, which are added to it to improve its machining or performance properties. Alloying elements are added to steel in various amounts and combinations (two, three, or more elements). Steel with up to 2.5 percent total alloying elements is called low-alloy steel; with 2.5–10.0 percent, medium-alloy steel; with more than 10 percent, high-alloy steel.

Alloy steels are classified according to structure or use. The following structural classes of alloy steel are distinguished:

(1) Steels of the pearlite class, which have the structure of pearlite or its variants (such as sorbite or troostite) or of pearlite with ferrite or hypereutectoid carbides.

(2) Steels of the martensite class, which are characterized by a reduced critical hardening rate and have a martensitic structure after normalizing.

(3) Steels of the austenite class, which have a sharply reduced austenite decomposition temperature, with austenite retained in the structure even at room temperature.

(4) Steels of the ferrite class, which contain elements that narrow the region of existence of austenite; such steels can retain the ferrite structure (sometimes together with carbides) at any temperature up to the melting point and after chilling at any rate.

(5) Steels of the carbide class contain an increased amount of carbon and carbide-forming elements; the structure of such steels is characterized by the presence of carbides (in the cast state, the ledeburite eutectic).

According to use, alloy steels are usually divided into structural steels, tool steels, and special-purpose steels (such as transformer, stainless, and high-temperature steels).

In the USSR, alloy steels are usually designated according to their chemical composition (for example, 18Kh2N4VA). The first number gives the average carbon content. For structural steel, the carbon content is given in hundredths of a percent; for tool steel, in tenths of a percent. The presence of alloying elements is given by the letter N for nickel, Kh for chromium, G for manganese, S for silicon, V for tungsten, F for vanadium, M for molybdenum, D for copper, K for cobalt, B for niobium, T for titanium, Iu for aluminum, R for boron, and A for nitrogen. The numbers after the letters indicate the approximate content of the corresponding element in percent. No number is given if the content of the element is about one percent or less. The letter A at the end of the designation indicates that the steel has a low sulfur and phosphorus content (that is, it is of high quality). The intended use of some steels is indicated by a letter. For example, R18 is high-speed steel with 18 percent tungsten, E3A is transformer steel with 3 percent silicon, and ShKh-15 is ball-bearing steel with 1.5 percent chromium. Some steels are designated by the letters EI or EP with a corresponding number (for example, EI69 or EP220); in most cases these are new steels undergoing testing and adoption in industry.

REFERENCES

Viaznikov, N. F. Legirovannaia stal’. Moscow, 1963.
Mes’kin, V. S. Osnovy legirovaniia stali, 2nd ed. Moscow, 1964.
Houdremont, E. Spetsial’nye stali, 2nd ed., vols. 1–2. Moscow, 1966. (Translated from German.)
Povolotskii, E. Ia., and A. K. Petrov. Proizvodstvo legirovannykh stalei. Moscow, 1967.

A. IA. STOMAKHIN