|Development of the Unified Numbering System
by Harold M. Cobb
Designation systems for metals and alloys in the United States
have traditionally been those established by various groups, including
metal producers; trade associations such as the Aluminum Association
(AA), the American Iron and Steel Institute (AISI), and the Copper
Development Association (CDA); professional societies such as
ASTM International, the American Welding Society (AWS), and the
Society of Automotive Engineers (SAE); and the U.S. government.
By the 1960s, it was becoming increasingly apparent that the traditional
approach to the designation of metals left some problem areas
that could not be satisfactorily solved. The following list of
some of these problems should make it clear that a case could
be made for developing an entirely new metals designation system.
Trade namesMany alloys were known only by trade names in cases where no central
organization assigned numbers. However, the technical societies
had policies prohibiting the use of trade names in their specifications.
Therefore, it became the practice, for nickel alloys, to list
the principal alloying elements as the designation. For example,
a well-known nickel alloy was given the designation Nickel-chromium-cobalt-molybdenum
alloy, a designation which was not particularly meaningful to
Same number for different alloysIt was not unusual for the various trade associations to assign
the same number to different alloys. For example, Alloy 205 could
be either a copper alloy, a nickel alloy, or a type of stainless
Different numbers for the same alloyThe AISI and SAE designated the same stainless steels by different
numbers, three digits for AISI and five digits for SAE.
Discontinued numbersThe AISI decided to discontinue the practice of designating numbers
for steels, and this was a particular problem with regard to the
assignment of designations to new stainless steels. ASTM was attempting
to fill the gap by issuing a new series of numbers for proprietary
stainless steels (e.g., XM-1, XM-2, XM-3, etc.)
Outmoded systemsCDAs three-digit system for the numbering of copper alloys was
outmoded, and a new system was being considered.
Variety of designationsThe U.S. government often had metal designations that differed
from those of other specification-writing bodies.
A New Numbering System
Because of these problems, in 1967 ASTM and SAE began to explore
the possibility of developing a new numbering system for metals
that would address the difficulties described above and provide
numbers for all alloys.
The U.S. Army was especially interested in this subject, and in
May 1969 the Army Materials and Mechanics Research Center (AMMRC)
issued a contract to SAE to conduct a Feasibility Study of a
Unified Numbering System for Metals and Alloys. This project
was jointly sponsored by ASTM and SAE, and a committee was appointed
to conduct the study. The committee was chaired by Norman L. Mochel,
a past president of ASTM, and consisted of the following members:
Herbert F. Campbell, Army Materials and Mechanics Research Center;
Harold M. Cobb, ASTM;
Alvin G. Cook, Allegheny Ludlum Steel Corp.;
Henry B. Fernald, Technical Consultant;
Muir L. Frey, Engineering Consultant;
S. T. Main, Grumman Aircraft Corp.;
Norman L. Mochel, Engineering Consultant;
R. Thomas Northrup, Society of Automotive Engineers;
Bruce A. Smith, General Motors Engineering Staff; and
Harry H. Stout, Phelps Dodge Copper Products Corp.
Development of the UNS
Some individuals consulted during the course of the 18-month feasibility
study expressed grave doubts about the possibility of establishing
an overall numbering system, but others thought it was worth exploring.
The major trade associations concerned with metals numbering systems
were also consulted, including the Aluminum Association, the American
Iron and Steel Institute, the Copper Development Association,
and the Steel Founders Society of America (SFSA). It was recognized
at the outset that any new system could be successful only if
these organizations were in general agreement with the concept.
In January 1971, the study was completed and a report was submitted
to the U.S. Army stating that it had been determined that a unified
numbering systems for metals was feasible and desirable. The report
included a general proposal of how such a system could be established
to provide a coherent designation system for all current and future
metals and alloys.
In April 1972, ASTM and SAE established an Advisory Board to further
develop and refine the proposed numbering system, The Advisory
Board consisted of the following members:
Chairman: Bruce A. Smith, General Motors Engineering Staff;
Secretaries: Harold M. Cobb, ASTM Staff;
R. Thomas Northrup, SAE Staff;
John Artman, Defense Industrial Supply Center;
Lawrence H. Bennett, National Bureau of Standards;
Alvin G. Cook, Allegheny Ludlum Steel Corp.;
Henry B. Fernald, Jr., Technical consultant;
John Gadbut, International Nickel Co.;
Joseph M. Engel, Republic Steel Corp. (representing AISI);
W. Stuart Lyman, Copper Development Association;
Robert E. Lyons, Federal Supply Service;
Norman L. Mochel, Metallurgical Consultant;
Edward F. Parker, General Electric Co.;
Richard R. Senz, The Aluminum Co. of America (for the Aluminum
Whitney Snyder, American Motors Corp.;
Rudolph Zillman, Steel Founders Society of America;
This board decided that the official name of the new all-encompassing
system would be the Unified Numbering System for Metals (UNS).
The major guiding principles of the system would be as follows:
Each designation for a metal or alloy should pertain to a specific
metal or alloy as determined by its unique chemical composition,
or to its mechanical properties or physical characteristics when
these are the primary defining criteria and the chemical composition
is secondary or not significant.
For ease of recognition, the numbers assigned should incorporate
numbers from existing numbering systems whenever possible.
The numbering system should be designed to accommodate current
metals and alloys, and to anticipate the need to provide numbers
for new alloys for the foreseeable future.
The system should be ideally-suited for computer use and for
the general indexing of metals and alloys.
Description of the System
In March 1974, the UNS Advisory Board completed the SAE/ASTM Recommended Practice for Numbering
Metals and Alloys. This established 18 series of designations,
which consisted of a prefix letter and five digits, as shown in
Table 1. Note that in most cases the letter is suggestive of the family
of metals identified.
The procedures for assigning numbers to each of the 18 series
of numbers was to be coordinated by the Advisory Board, but the
specific details for each series would be developed by experts
in each of those fields. Examples of some of these designations
are shown in Table 2.
By 1974, the Advisory Board had coordinated the establishment
of specific UNS designations for over 1000 metals and alloys,
including steel, stainless steel, tool steel, superalloys, aluminum,
copper, cobalt, magnesium, and nickel. These designations were
listed in the first edition of a UNS Handbook, which was published
in 1975. Each entry in the book included the UNS designation,
a brief description of the alloy, the chemical composition of
the alloy, and a list of the national specifications in which
the alloy appeared. A typical entry from the book is shown in
UNS Achievements Over 25 Years
The UNS designation system has been a highly successful venture
from many standpoints. It has provided satisfactory solutions
to the six problem areas discussed earlier in this article. Metals
and Alloys in the Unified Numbering System, published jointly
by ASTM and SAE, lists over 5000 UNS designations in the recently-published
ninth edition. It is also significant to note that this publication
has been adopted by the Department of Defense (DoD) as a replacement
for MIL-HDBK-H1, Cross Index of Chemically Equivalent Specifications
and Identification Code (Ferrous and Nonferrous Alloys).
The Copper Development Association, in a sweeping change, replaced
all of the traditional three-digit CDA numbers with UNS designations,
and the American Welding Society now references UNS designations
in all AWS specifications for welding filler metal and electrodes.
A large percentage of ASTM specifications include UNS references
and, for new stainless steel alloys and most nickel alloys, UNS
is the only designation listed.
Virtually all of the metals reference books published in the last
20 years have adopted UNS as their principal indexing systems
and many metal producers now reference the UNS designations in
their literature. //
For More Information
James D. Redmond, TMR Stainless, Pittsburgh, Pa. 15327-6423 (phone: 412/369-0377).
Copyright 2002, ASTM