2-Metals Codes - The UNS
The UNS Standard is a relatively new standard. It is gaining in acceptance and will soon be the single metals Standard in the USA. But some history is in order before commencing:

The American Iron and Steel Institute (AISI) has a standard that is widely accepted in the United States and other countries. However it does not cover all metals and, in many instances, it does not convey enough information to speak to all of the attributes of some metals. Therefore two United States standards organizations, ASTM (American Society for Testing and Metals) and SAE (Society of Automotive Engineers), have developed a standard for classification of metals that is independent of AISI standards, the UNS. It is composed of seventeen letters that represent seventeen metals types. Each letter is followed by five digits that signify the specific makeup of each of these metals types. The first three or four digits are derived from different standards.

List of UNS metals designations (only those underlined are important to machinists)

  • AXXXXX Aluminum
  • CXXXXX Copper and copper alloys
  • EXXXXX Rare earth and rare earth like (cerium, actium, etc.)
  • FXXXXX Cast iron
  • GXXXXX Carbon steel
  • LXXXXX Low melting point alloys (lead, cadmium, mercury, etc.)
  • MXXXXX Misc. non-ferrous metals alloys (antimony, arsenic, uranium, etc.)
  • NXXXXX Nickel and nickel alloys
  • PXXXXX Precious metals (gold, silver, etc.)
  • RXXXXX Reactive and refractory metals and alloys (boron, vanadium, etc.)
  • SXXXXX Stainless steel
  • TXXXXX Tool Steel
  • WXXXXXWelding filler materials
  • ZXXXXX Zinc and zinc alloys

Following are two examples of UNS designators and how they relate to AISE/SAE designations (notice how the older standard numbers have been incorporated into the UNS)

  1. UNS designation "G10300" represents an AISI/SAE 1030 carbon steel
  2. UNS designation "S31600" represents an AISI/SAE 316 stainless steel

Since the AISE/SAE standards have only three or four digits the last unused digit(s) in the UNS system can be used for added information such as tempering or manufacturing methods. At this writing all of these digits are not fully utilized but will surely be used in the near future.

Note that the UNS standard is not yet widely used in the machine shop. However, since it is gaining acceptance with engineers and purchasing agents it will soon become the standard on the shop floor. In the interim UNS can be easily translated from AISI and SAE designators and visa versa.