ALLOY STEELS
In general, the term applies to all steels exceeding the limits of manganese, silicon, and copper of carbon steels or which contain other alloying ingredients. Alloy steels often take the name of the alloying element or elements having the greatest influence on their performance characteristics or the name of a key characteristic, processing mechanism, or application. Thus, the prevalence of such terms as nickel steels; stainless, or corrosion-resistant, steels; marag-ing steels; precipitation-hardening steels; tool steels; valve steels, etc. Usually, however, the term excludes high-alloy steels and refers instead to the standard alloy steels of the American Iron and Steel Institute (AISI) and SAE International, which contain low to moderate amounts of alloying elements, usually less than 5% total. The AISI or SAE designations of these steels are usually noted by four numerals—13XX to 91XX. The first two numerals pertain to the specific alloying element or elements, and the last two numerals indicate carbon content in hundredths of 1%. Sometimes three numerals are used to denote carbon content, and a letter, such as B for boron and L for lead, follows the first two numerals to indicate an alloying element not indicative of the first two numerals. A letter prefix is used occasionally to designate special furnace practice used to make the steel, and the suffix H is used to designate steels made to specific hardenability requirements. A three-numeral system, 9XX, is commonly used to designate high-strength, low-alloy (HSLA) steels, some of which are also called microalloyed steels because of the small amount of alloying elements, with the last two numerals indicating minimum tensile yield strength in 1,000 lb/in2 (6.895 MPa). Although most alloy steels are heat-treated by users and extremely high levels of strength and toughness can be achieved, HSLA steels are typically supplied to specific strength levels and are not heat-treated by users.

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