What is the Unified Numbering System (UNS) for Metals and Alloys?

To overcome the problems of traditional material numbering systems developed during the 1960s for distinguishing each material separately and standardize, a study was conducted. After an 18-month feasibility study and discussions with AISI, the Aluminum Association, the Copper Development Association, and the Steel Founders’ Society of America, the team recommended establishing the Unified Numbering System (UNS). The UNS numbering system is used by many engineering industries and is accepted globally.

What is a Unified Numbering System

The Unified Numbering System or UNS is a metal and alloy designation system managed jointly by ASTM International and SAE International. Each specific metal or alloy is assigned a UNS number that defines mainly its specific chemical composition, and sometimes specific mechanical or physical properties. So, the unified numbering system basically is a composition-based material numbering system where each metal/alloy is identified with a letter followed by five numbers.

Note that, a UNS number alone does not serve as the full specification of that material as it does not establish any requirements for material properties, heat treatment, form, or quality. A document SAE HS-1086 gives a cross-reference for various designation systems and the chemical composition of materials. Currently, there are more than 5200+ UNS designations for different metals and alloys.

Difference between UNS number and Material Specification

A UNS number only provides a specific chemical composition. The full material specification is not provided in the UNS number. Other material requirements such as mechanical properties, heat treatment, form, purpose, and testing methods are specified in the respective material specification. Various trade and professional organizations prepare these material specifications. Within a material specification, a number of different UNS numbers may be included.

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UNS Number Format

Each UNS number is structured with a letter followed by five digits that designate the composition of the material. They have 18 series to identify metals and alloys. Out of these 18 series, 9 are for ferrous metals and alloys and the other 9 are for non-ferrous metals and alloys.

Letters used in the unified numbering system are A for Aluminum and Aluminum alloys, C for copper and copper alloys, D for specified mechanical property steels, E for Rare earth and rare earthlike metals and alloys, F for cast Irons, G for AISI and SAE carbon and alloy steels, H for AISI and SAE H-steels, J for Cast steels, K for Miscellaneous other steels and ferrous alloys, L for Low-melting metals and alloys, M for Miscellaneous nonferrous metals and alloys, N for Nickel and nickel alloys, P for Precious metals and alloys, R for Reactive and refractory metals and alloys, S for Stainless Steels, T for Tool Steels, W for Welding filler metals, and Z for Zinc and zinc alloys.

The first 3 digits usually match older 3-digit numbering systems, while the last 2-digits indicate modern variations. To give an 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. Sometimes the suffix digits represent a material property specification. For example, “08” in UNS S31008 represents the maximum allowed carbon content of that material is 0.08%.

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Examples of Unified Numbering System for Common materials

Some of the common materials and translations to other standards are:

  • UNS S31600 is SAE 316
  • 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 S31603 is 316L, a low-carbon version of 316. The digit “03” was assigned since the maximum allowed carbon content is 0.03%
  • UNS C90300 is CDA 903

Refer to the table below which provides the description of numbers in the UNS numbering system.

A00001-A99999Aluminum and aluminum alloys
A01001-A63562Aluminum Foundry Alloys, Ingot, or Casting
A82014-A87475Wrought Aluminum Alloys Clad with Wrought Aluminum Alloys, Non- or Heat Treatable
A91030- A91450Wrought Aluminum Alloys, Non-Heat Treatable
A93002-A95954Wrought Aluminum Alloys, Non-Heat Treatable
A98001-A98280Wrought Aluminum Alloys, Non-Heat Treatable
A92001-A92618Wrought Aluminum Alloys, Heat Treatable
A96002-A97472Wrought Aluminum Alloys, Heat Treatable
C00001-C99999Copper and copper alloys
Wrought Alloys 
C10100-C15760Pure and Low Alloyed Copper (>99%Cu)
C16200-C16500Cadmium Copper
C17000-C17700Copper-Beryllium Alloy (Beryllium Bronzes)
C18000-C19900Copper and High Copper Alloys (>96%Cu)
C20500-C29800Brasses (Cu-Zn)
C31000-C35600Leaded Brasses (Cu-Zn-Pb )
C40400-C49080Tin Brasses (Cu-Zn-Sn-Pb)
C50100-C52900Phosphor bronzes (Cu-Sn-P)
C53200-C54800Leaded Phosphor Bronzes
C55180-C56000Cu-Ag-P and Cu-P Brazing Filler Metal
C60600-C64400Aluminum Bronzes
C64700-C66100Silicon Bronzes
C66200-C66420Copper Alloys
C66700-C67820Manganese Bronzes
C68000-C69950Silicon Brasses and Other Copper-Zinc Alloys
C70100-C72950Copper-Nickel Alloys
C73150-C79900Nickel Silvers and Leaded Nickel Silvers
Cast alloys 
C80100-C81200Cast Coppers (>99%Cu)
C81300-C82800Cast Chromium Copper and Beryllium Copper Alloys (>96%Cu)
C83300-C85800Cast Red, Yellow and Leaded Brasses
C86100-C86800Cast Manganese Bronzes and Leaded Manganese Bronzes
C87300-C87900Cast Silicon Brasses and Bronzes
C89320-C89940Cast Cu-Sn-Bi-(Se, Zn, Ni) Alloys
C90200-C94500Tin Bronzes and Leaded Tin Bronzes
C94700-C94900Cast Nickel-Tin Bronzes
C95200-C95810Cast Aluminum Bronzes
C96200-C96800Cast Copper-Nickel Alloys
C97300-C97800Cast Nickel-Silver Alloys
C98200-C98840Cast Leaded Copper Alloys
C99300-C99750Cast Copper Alloys
D00001-D99999Steels with specified mechanical properties
D40450-D40900Carbon Steels
D50400-D52101Alloy Steels Casting
E00001-E99999Rare earth and rare earth-like metals and alloys
E21000-E45999Mixed rare earth
F00001-F99999Cast irons
F 10001-F15501Cast Iron, Gray
F 10090-F10920Cast Iron Welding Filler Metal
F 20000-F22400Cast Iron, Malleable
F 22830-F26230Cast Iron, Pearlitic Malleable
F 30000-F36200Cast Iron, Ductile (Nodular)
F 41000-F41007Cast Iron, Gray, Austenitic
F 43000- F43030Cast Iron, Ductile (Nodular), Austenitic
F45000 F 45009Cast Iron, White
F47001-F47006Cast Iron, Corrosion
G00001-G99999AISI and SAE carbon and alloy steels (except tool steels)
G10050-G10950Carbon Steel
G15130-G15900Carbon Steel
G11080-G11510Desulfurized Carbon Steel
G12110-G12150Rephosphorized and Resulfurized Carbon Steel
G13300-G13450Mn Alloy Steel
G40120-G48200Mo Alloy Steel, Cr-Mo Alloy Steel, Ni-Cr-Mo Alloy Steel, Ni-Mo Alloy Steel
G81150-G88220Ni-Cr-Mo Alloy Steel
G50150-G52986Cr Alloy Steel, Cr-B Alloy Steel
G61180-G61500Cr-V Alloy Steel
G92540-G98500Cr-Si Alloy Steel, Si-Mn Alloy Steel, Cr-S-Mn Alloy Steel, Ni-Cr-Mo Alloy Steel, Ni-Cr-Mo-B Alloy Steel
H00001-H99999AISI and SAE H-steels
H10380-H15621H-Carbon Steel, C-Mn H-Alloy Steel, C-B H Carbon Steel, Mn H-Carbon Steel, B- Mn H -Carbon Steel
H40270-H48200C-Mo H-Alloy Steel, Cr-Mo H-Alloy Steel Ni-Mo H-Alloy Steel
H50401-H51601C-Cr-B H-Alloy Steel, C-Cr H-Alloy Steel
H61180-H61500Cr-V H-Alloy Steel
H81451-H94301Ni-Cr-Mo H-Alloy Steel
J00001-J99999Cast steels (except tool steels)
J01700-J05003Carbon Steel Casting
J11442-J84090Alloy Steel Casting
J91100-J92001Austenitic Manganese Steel Casting, Alloy Steel Casting
J92110-J93000Alloy Steel Casting Precipitation Hardening, Alloy Steel Casting, Cast Cr-Ni-Mo Stainless Steel, Cast Cr-Ni Stainless Steel, Cast Cr-Mn-Ni-Si-N Stainless Steel
J93001-J95705Stainless Steel Casting, Cast Cr-Ni-Mo Stainless Steel, Alloy Steel Casting, Maraging Cast Ferritic-Austenitic Stainless Steel, Duplex Alloy Steel Casting, Alloy Steel Casting
K00001-K99999Miscellaneous steels and ferrous alloys
K00040-K08500Carbon Steel, Carbon Steel with Special Magnetic Properties, Steel Welding Rod, Enameling Steel
K10614-K52440Alloy Steel, Alloy Steel Electrode and Welding Wire, High-Strength Low-Alloy Steel
K90901-K95000Alloy Steel, Superstrength; Ferritic Cr-Mo-V Steel; Manganese Steel, Nonmagnetic; Ni-Co Steel Welding Wire; Iron, Electrical Heating Element Alloy; Iron Thermostat Alloy; Martensitic Age-Hardenable Alloy; Maraging Alloy; Fe-Co Soft Magnetic Alloy; Nickel Steel; Invar; Iron, Nickel Sealing Alloy; etc.
L00001-L99999Low-melting metals and alloys
M00001-M99999Miscellaneous nonferrous metals and alloys
N00001 to N99999Nickel and nickel alloys
P00001-P99999Precious metals and alloys
R00001-R99999Reactive and refractory metals and alloys
R04001.R04999Niobium (Columbium)
S00001-S99999Heat and corrosion-resistant steels (stainless), valve steels, iron-base “superalloys
S13800-S17780Precipitation Hardenable Cr-Ni-Al-Mo-(Cu, Ti) Stainless Steels
S20100-S39000Austenitic Cr-Mn-Ni (Si, Mo, Cu, Al) Stainless Steel; Thermal Spray Wire; Austenitic Cr-Mn-Ni Stainless Steel and Welding Filler Metal; Austenitic Cr-Ni Heat-Resisting Steel and Welding Filler Metal; Precipitation Hardenable Cr-Ni-(Si, Ti, Mo, Al) Stainless Steel, etc.
S40300-S46800Martensitic Cr Stainless Steel; Ferritic Cr Stainless Steel with Ti or Ni or Mo; Martensitic Cr-Ni-Mo Stainless Steel; Hardenable Cr Stainless Steel
S50100-S50500Cr Heat Resisting Steels and Filler Metal
S63005-S64007Valve Steel
S65006-S65007Valve Steel
S65150-S67956Iron Base Superalloy
T00001-T99999Tool steels, wrought, and cast
T11301-T12015High-Speed Tool Steels
T20810-T20843Hot-Work Tool Steels
T30102-T 30407Cold Work Tool Steels
T31501-S31507Oil-Hardening Steels
T41901-T41907Shock-Resisting Tool Steels
T51602-T51621Mold Steels
T60601-T60602C-W Tool Steels
T61202-T61206Low-Alloy Tool Steels
T72301-T72305Water Hardening Tool Steels
T74000-T75008Cr-Steels Solid Welding Wire for Machinable Surfaces and Tool and Die Surfaces
T87510-T87520Thermal Spray Wire
T90102-T91907Cast Tool Steels
W00001-W99999Welding filler metals, classified by weld deposit composition
W60000-W69999Copper base alloys
W70000-W79999Surfacing alloys
W80000-W89999Nickel base alloys
Z00001-Z99999Zinc and zinc alloys
Table 1: UNS Numbering System for Metals and Alloys

Importance of UNS (Unified Numbering System)

Various trade associations, societies, and individual users and producers of metals and alloys use the UNS system to avoid confusion. The system provides a uniform approach and proficient indexing which helps in record keeping, data storage, retrieval, and cross-referencing. Using UNS numbers metal and alloy identification becomes much easier.

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

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