Metal Codes
There are two systems for identifying different metals. One is the combined standards of American Iron & Steel Institute (AISI) and Society of Automotive Engineers (SAE). The second system is the newer United Numbering System.
AISI/SAE Metal Designation System
With one exception the first digit signifies the major alloy used in the steel. Carbon steels are not alloyed.
Key to the AISI/SAE steel numbering system
The first two numbers in this designation signify the primary alloy(s) of the steel. The next two numbers in the designation signify the amount of carbon present in the steel.
- Carbon Steels:
- The first digit is “1” as in 10xx, 11xx, and 12xx
- The second digit describes processing: “1”, e.g. 11xx, is resulfurized and “2”, e.g. 12xx, is resulfurized and rephosphorized.
- Manganese Steel:
- The first digit is “1” as in 13xx and is, indeed, a carbon steel. However, since manganese is a normal by-product of carbon steel making the AISI/SAE has decided not to classify it as an alloy steel.
- The second digit is always “3”
- Nickel Steel:
- The first digit is “2” as in 23xx and 25xx
- The second digit designates the percentage of nickel in the steel.
- Nickel-Chromium Steel:
- The first digit is “3” as in 31xx, 32xx, and 33xx,
- The second digit designates the percentage of nickel and chromium in the steel.
- Molybdenum Steels:
- The first digit is “4” as in 40xx and 44xx.
- The second digit designates the percentage of molybdenum in the steel.
- Chromium Steel:
- The first digit is “5” as in 51xx and 52xx
- The second digit designates the percentage of chromium in the steel.
- Chromium-Vanadium Steel:
- The first digit is “6” as in 61xx
- The second digit designates the percentage of chromium and vanadium in the steel.
- Tungsten-Chromium Steel:
- The first digit is “7” as in 72xx
- The second digit designates the percentage of tungsten and chromium
- Silicon-Manganese Steel:
- The first digit is “9” as in 92xx
- The second digit designates the percentage of silicon and manganese in the steel.
- Triple Alloy Steels:
- These steels contain three alloys
- The first digit can be “4”, “8”, or “9” depending on the predominate alloy
- The second digit designates the percentage of the reaming two alloys.
As shown, the AISI / SAE steel designation system gives information about the chemical composition of the steel (alloy type and carbon content). However, in many cases, this is not enough information for the purchasing company to procure the steel. The ASTM specification of fabrication methodology will often be added to the material specifications demonstrated but fabrication methods will not be discussed here. This is one reason why the Unified Numbering System (UNS), which provides more specific information of a metal’s content, emerged for more precise manufacturing requirements.
Following are two examples of UNS designators and how they relate to AISE/SAE designations:
- A resulfurized carbon steel containing 0.21% carbon would be UNS G11210 or AISI/ASE 1121
- A steel alloyed with 20% chromium and vanadium and containing 0.75% carbon would be UNS G62750 or AISI/SAE 6275
Unified Numbering System (UNS)
The Unified Numbering System (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 metal types. Each letter is followed by five digits that signify the specific makeup of each of these metal types. The first three or four digits are derived from different standards.
United Number System (UNS) Categories
UNS series Metal Types
A00001 to A99999 Aluminum and aluminum alloys
C00001 to C99999 Copper and copper alloys (brasses and bronzes)
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
(except tool steels)
H00001 to H99999 AISI and SAE H-steels
J00001 to J99999 Cast steels (except tool 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
M1xxxx – Magnesium Alloys
N00001 to N99999 Nickel and nickel alloys
P00001 to P99999 Precious metals and alloys
R00001 to R99999 Refractory metals and alloys
R03xxx- Molybdenum Alloys
R04xxx- Niobium (Columbium) Alloys
R05xxx- Tantalum Alloys
R3xxxx- Cobalt Alloys
R5xxxx- Titanium Alloys
R6xxxx- Zirconium Alloys
S00001 to S99999 Heat and corrosion resistant (stainless) steels
T00001 to T99999 Tool steels, wrought and cast
W00001 to W99999 Welding filler metals
Z00001 to Z99999 Zinc and zinc alloys
Above is the complete list of UNS metals designations.
Below are the basic metals important to machinists and welders.
Important UNS metal designations to machinists and welders
AXXXXX Aluminum
CXXXXX Copper and copper alloys
FXXXXX Cast iron
GXXXXX Carbon steel
NXXXXX Nickel and nickel alloys
SXXXXX Stainless steel
TXXXXX Tool Steel
WXXXXX Welding 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)
- UNS designation “G10300” represents an AISI/SAE 1030 carbon steel
- 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 vice versa.
Derived from Unified numbering system – Wikipedia. Available and accessed online 30 January 2024, and The Virtual Machine Shop (http://www.jjjtrain.com/vms/eng_metal_stds/eng_metal_stds_02.html and http://www.jjjtrain.com/vms/eng_metal_stds/eng_metal_stds_03.html) accessed and available via the WayBack Machine 15 January 2024.