The unified numbering system (UNS) is an

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...

designation system widely accepted in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

. Each UNS number relates to a specific metal or alloy and defines its specific chemical composition, or in some cases a specific mechanical or physical property. A UNS number alone does not constitute a full material specification because it establishes no requirements for material properties, heat treatment, form, or quality.

History

During the early 20th century many different metal alloys were developed in isolation within certain industries to meet the needs of that industry. This allowed a wide variety of competing standards, compositions and designations to flourish. By the 1960s there were a number of differing numbering or designation schemes for various alloys. This meant that the same number might be used for different alloys, different numbers might be used for the same alloy or different trade names might indicate similar or wildly different alloys. Additionally, the increasing number of new alloys meant that the problem would only get worse. In January 1971, an 18 month study recommended that a unified system would be possible and helpful. An advisory board was established in April 1972 to establish the Unified Numbering System (UNS). The UNS is managed jointly by the ASTM International and SAE International. The resulting document

SAE SAE or Sae may refer to: Science and technology : * Selective area epitaxy, local growth of epitaxial layer through a patterned dielectric mask deposited on a semiconductor substrate * Serious adverse event, in a clinical trial * Simultaneous Aut ...

HS-1086 provides a cross-reference between various designation systems and the chemical composition.

UNS number vs material specification

A UNS number only defines a specific chemical composition, it does not provided full material specification. Requirements such as material properties (

yield strength In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and wi ...

, ultimate strength,

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

, etc.), heat treatment, form ( rolled,

cast Cast may refer to: Music * Cast (band), an English alternative rock band * Cast (Mexican band), a progressive Mexican rock band * The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis * ''Cast'', a 2012 album by Trespassers William ...

, forged,

flange A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...

s, tubes, bars, etc.), purpose (high temperature, boilers and pressure vessels, etc) and testing methods are all specified in the material or standard specification which is created by various trade and professional organizations. Many material or standard specifications include a number of different UNS numbers that may be used within that specification. For example: UNS S30400 (SAE 304, Cr/Ni 18/10, Euronorm 1.4301 stainless steel) could be used to make stainless steel bars ( ASTM A276) or stainless steel plates for pressure vessels ( ASTM A240) or pipes ( ASTM A312). Conversely, A312 pipes could be made out of about 70 different UNS alloy steels.

Format

It consists of a prefix letter and five digits designating a material composition. For example, a prefix of S indicates

stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...

alloys, C indicates

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...

brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wi ...

, or

bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids suc ...

alloys, T indicates tool steels, and so on. The first 3 digits often match older 3-digit numbering systems, while the last 2 digits indicate more modern variations. For example, Stainless Steel Type 310 in the original 3-digit system became S31000 in the UNS System. The more modern low-carbon variation, Type 310S, became S31008 in the UNS System. Often, the suffix digit is chosen to represent a material property specification. For example, "08" was assigned to UNS S31008 because the maximum allowed carbon content is 0.08%.

Common materials

Some common materials and translations to other standards: * UNS K11547 is T2 tool steel * UNS S17400 is ASTM grade 630, Cr-Ni 17-4PH precipitation hardened stainless steel * UNS S30400 is SAE 304, Cr/Ni 18/10, Euronorm 1.4301 stainless steel * UNS S31600 is SAE 316 * UNS S31603 is 316L, a low carbon version of 316. The digits "03" were assigned since the maximum allowed carbon content is 0.03% * UNS C90300 is CDA 903

References

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External links