Unified numbering system
The unified numbering system is an alloy designation system widely accepted in North America. 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. The UNS is managed jointly by the ASTM International and SAE International. The resulting document SAE 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, heat treatment, form, purpose 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 could be used to make stainless steel bars or stainless steel plates for pressure vessels or pipes. 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 alloys, C indicates copper, brass, or bronze 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
| UNS series | Metal type |
| A00001 to A99999 | Aluminum and aluminum alloys |
| C00001 to C99999 | Copper and copper alloys |
| D00001 to D99999 | Specified mechanical property steels |
| E00001 to E99999 | Rare earth and rare earthlike metals and alloys |
| F00001 to F99999 | Cast irons |
| G00001 to G99999 | AISI and SAE carbon and alloy steels |
| H00001 to H99999 | AISI and SAE H-steels |
| J00001 to J99999 | Cast steels |
| K00001 to K99999 | Miscellaneous steels and ferrous alloys |
| L00001 to L99999 | Low-melting metals and alloys |
| M00001 to M99999 | Miscellaneous nonferrous metals and alloys |