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.
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%.
Martensitic Cr Stainless Steel; Ferritic Cr Stainless Steel with Ti or Ni or Mo; Martensitic Cr-Ni-Mo Stainless Steel; Hardenable Cr Stainless Steel
S50100-S50500
Cr Heat Resisting Steels and Filler Metal
S63005-S64007
Valve Steel
S65006-S65007
Valve Steel
S65150-S67956
Iron Base Superalloy
T00001-T99999
Tool steels, wrought, and cast
T11301-T12015
High-Speed Tool Steels
T20810-T20843
Hot-Work Tool Steels
T30102-T 30407
Cold Work Tool Steels
T31501-S31507
Oil-Hardening Steels
T41901-T41907
Shock-Resisting Tool Steels
T51602-T51621
Mold Steels
T60601-T60602
C-W Tool Steels
T61202-T61206
Low-Alloy Tool Steels
T72301-T72305
Water Hardening Tool Steels
T74000-T75008
Cr-Steels Solid Welding Wire for Machinable Surfaces and Tool and Die Surfaces
T87510-T87520
Thermal Spray Wire
T90102-T91907
Cast Tool Steels
W00001-W99999
Welding filler metals, classified by weld deposit composition
W60000-W69999
Copper base alloys
W70000-W79999
Surfacing alloys
W80000-W89999
Nickel base alloys
Z00001-Z99999
Zinc 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.
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.
3 thoughts on “What is the Unified Numbering System (UNS) for Metals and Alloys?”
In industries where safety is paramount, like oil and gas, monitoring environmental conditions is essential. One such tool that plays a critical role in these industries is the wind sock. This...
Whatispiping Team, in association with Everyeng, is conducting an online pre-recorded Comprehensive Piping Stress Analysis Certificate course to help mechanical and piping engineers. Along with the...
Thanx for your list of UNS numbers.
What is PE195
Can we assign UNS numbers to JIS materials?