Harold M. Cobb*Metallurgical ConsultantKennett Square, Pennsylvania

Designation systems for metals and alloysin the United States have traditionally beenthose established by various groups, in-cluding metal producers; trade associa-

tions such as the Aluminum Association (AA), theAmerican Iron & Steel Institute (AISI), and theCopper Development Association (CDA); profes-sional societies such as the American Society forTesting and Materials (ASTM), the AmericanWelding Society (AWS), and the Society of Auto-motive Engineers (SAE); and the U. S. government.

By the 1960s, it was becoming increasingly ap-parent that the traditional approach to the designa-tion of metals left some problem areas that couldnot be satisfactorily solved. The following list of someof these problems should make it clear that a casecould be made for developing an entirely new metalsdesignation system:

• Trade names: Many alloys were known only bytrade names in cases where no central organiza-tion assigned numbers. However, the technical so-cieties had policies prohibiting the use of tradenames in their specifications. Therefore, it becamethe practice, for nickel alloys, to list the principal al-loying elements as the designation. For example,a well-known nickel alloy was given the designation“Nickel-chromium-cobalt-molybdenum alloy,” a des-ignation which was not particularly meaningful tomost readers.

• Same number for different alloys: It was not un-usual for the various trade associations to assignthe same number to different alloys. For example,Alloy 205 could be either a copper alloy, a nickelalloy, or a type of stainless steel.

• Different numbers for the same alloy: The AISIand SAE designated the same stainless steels byd i f -

*Life member of ASM International

ferent numbers, three digits for AISI and five digits forSAE.

• Discontinued numbers: The AISI decided to dis-continue the practice of designating numbers forsteels, and this was a particular problem with re-gard to the assignment of designations to new stain-less steels. ASTM was attempting to fill the gap byissuing a new series of numbers for proprietary stain-less steels (e.g., XM-1, XM-2, XM-3, etc.)

• Outmoded systems: CDA’s three-digit systemfor the numbering of copper alloys was outmoded,and a new system was being considered.

• Variety of designations: The U.S. governmentoften had metal designations that differed fromthose of other specification-writing bodies.

A new numbering systemBecause of these problems, in 1967 the Amer-

ican Society for Testing and Materials (ASTM) andthe Society of Automotive Engineers (SAE) beganto explore the possibility of developing a new num-bering system for metals that would address the dif-ficulties described above and provide numbers for allalloys.

The U.S. Army was especially interested in thissubject, and in May 1969 the Army Materials andMechanics Research Center (AMMRC) issued acontract to the SAE to conduct a “Feasibility Study of

This article reviews the Unified Numbering System for Metals and Alloys—what it is, why it was conceived, and how it was developed.

Organization of UNSThe UNS, jointly sponsored by the American

Society for Testing and Materials (ASTM) andthe Society of Automotive Engineers (SAE), isoperated in accordance with ASTM E527/SAE J1086, Recommended Practice for NumberingMetals and Alloys. The organization for admin-istering the UNS consists of an advisory board,three number-assigning offices, a corps of vol-unteer consultants, and staffs at ASTM and SAE.Dr. James D. Redmond is the current chairmanof the UNS Advisory Board.

Development of the

UNIFIED NUMBERINGSYSTEM

ADVANCED MATERIALS & PROCESSES/FEBRUARY 2002 47

a Unified Numbering System for Metals and Alloys.”This project was jointly sponsored by ASTM andSAE, and a committee was appointed to conductthe study. The committee was chaired by Norman L.Mochel, a past president of ASTM, and consistedof the following members:

Herbert F. Campbell, Army Materials and Mechanics Research Center

Harold M. Cobb, American Society for Testing and Materials

Alvin G. Cook, Allegheny Ludlum Steel Corp.Henry B. Fernald, Technical ConsultantMuir L. Frey, Engineering ConsultantS. T. Main, Grumman Aircraft Corp.Norman L. Mochel, Engineering ConsultantR. Thomas Northrup, Society of Automotive

EngineersBruce A. Smith, General Motors Engineering StaffHarry H. Stout, Phelps Dodge Copper Products

Corp.

Development of the UNSSome individuals consulted during the course of

the eighteen-month feasibility study expressed gravedoubts about the possibility of establishing an overallnumbering system, but others thought it was worthexploring. The major trade associations concernedwith metals numbering systems were also consulted,including the Aluminum Association, the AmericanIron & Steel Institute, the Copper Development As-sociation, and the Steel Founders’ Society ofAmerica (SFSA). It was recognized at the outsetthat any new system could be successful only ifthese organizations were in general agreement withthe concept.

In January 1971, the study was completed anda report was submitted to the U.S. Army stating thatit had been determined that a unified numberingsystems for metals was feasible and desirable. Thereport included a general proposal of how such asystem could be established to provide a coherentdesignation system for all current and future metalsand alloys.

In April 1972, ASTM and SAE established an Ad-visory Board to further develop and refine the pro-posed numbering system The Advisory Board con-sisted of the following members:

Chairman: Bruce A. Smith, General Motors Engineering Staff

Secretaries: Harold M. Cobb, ASTM StaffR. Thomas Northrup, SAE Staff

Members:John Artman, Defense Industrial Supply CenterLawrence H. Bennett, National Bureau of

StandardsAlvin G. Cook, Allegheny Ludlum Steel Corp.Henry B. Fernald, Jr., Technical consultantJohn Gadbut, International Nickel Co.Joseph M. Engel, Republic Steel Corp.

(representing AISI)W. Stuart Lyman, Copper Development

AssociationRobert E. Lyons, Federal Supply ServiceNorman L. Mochel, Metallurgical ConsultantEdward F. Parker, General Electric Co.Richard R. Senz, The Aluminum Co. of America

Table 1— Primary series of UNS numbersUNS series Metal group UNS series Metal group

Axxxxx Aluminum and aluminum alloys Lxxxxx Low melting metals and alloysCxxxxx Copper and copper alloys Mxxxxx Miscellaneous nonferrous metals & alloysDxxxxx Steels—designated by mechanical property Nxxxxx Nickel and nickel alloysExxxxx Rare earth and rare earth-like alloys Pxxxxx Precious metal and alloysFxxxxx Cast irons Rxxxxx Reactive and refractory metals and alloysGxxxxx AISI and SAE carbon and alloy steels Sxxxxx Stainless steels, valve steels, superalloysHxxxxx AISI H-steels Txxxxx Tool steelsJxxxxx Cast steels Wxxxxx Welding filler metals Kxxxxx Miscellaneous steels and ferrous alloys Zxxxxx Zinc and zinc alloys

Table 2—Examples of UNS designationsUNS Traditional designation

A03190 AA 319.0 (Aluminum alloy casting)A92024 AA 2024 (Wrought aluminum alloy)C26200 CDA 262 (Cartridge brass)G12144 AISI 12L14 (Leaded alloy steel)G41300 AISI 4130 (Alloy steel)K93600 Invar (36% nickel alloy steel)L13700 Alloy Sn 70 (Tin-lead solder)N06007 Nickel-chromium alloy (Hastelloy G)N06625 Alloy 625 (Nickel-chromium-molybdenum-columbium

alloy)R58210 Alloy 21 (Titanium alloy)S30452 AISI 304N (Stainless steel, high nitrogen)S32550 Ferralium 255 (Duplex stainless steel)T30108 AISI A-8 (Tool steel)W30710 AWS E307 (Stainless steel electrode)Z33520 Alloy AG40A (Zinc alloy)

Tabel 3 — A typical entry from metals and alloys in the Unified Numbering SystemNickel and Nickel Alloys

Unified Number Description Chemical Composition Cross-reference Specifications

N1003 Ni-Mo Alloy. Al 0.50max B0.010max C0.04-0.08 Co 0.20 max AMS 5607; 5771 Solid solution Cr 6.0-8.0 Cu 0.35 max Fe 5.0 max Mn 1.00 max ASME SB434; SFA5.14 (ERNiMo-2) strengthened Mo 15.0-18.0 Ni rem P 0.15 max S 0.020 max ASTM B366; B573 (Hastelloy N) Si 1.00 max V 0.50 max W 0.50 max AWS A5.14 (ERNiMo-2)

48 ADVANCED MATERIALS & PROCESSES/FEBRUARY 2002

(for the Aluminum Assoc.)Whitney Snyder, American Motors Corp.Rudolph Zillman, Steel Founders’ Society

of AmericaThis Board decided that the official name of the

new all-encompassing system would be the “Uni-fied Numbering System for Metals (UNS).” Themajor guiding principles of the system would be asfollows:

• Each designation for a metal or alloy should per-tain to a specific metal or alloy as determined by itsunique chemical composition, or to its mechanical properties or physical characteristicswhen these are the primary defining criteria and thechemical composition is secondary or not significant.

• For ease of recognition, the numbers assignedshould incorporate numbers from existing num-bering systems whenever possible.

• The numbering system should be designed toaccommodate current metals and alloys, and to an-ticipate the need to provide numbers for new alloysfor the foreseeable future.

• The system should be ideally suited for com-puter use and for the general indexing of metalsand alloys.

Description of the systemIn March 1974, the UNS Advisory Board com-

pleted the “SAE/ASTM Recommended Practice forNumbering Metals and Alloys.” This establishedeighteen series of designations, which consisted ofa prefix letter and five digits, as shown in Table 1.Note that in most cases the letter is suggestive ofthe family of metals identified.

The procedures for assigning numbers to each ofthe 18 series of numbers were to be coordinatedby the Advisory Board, but the specific details foreach series would be developed by experts in eachof those fields. Examples of some of these desig-nations are shown in Table 2.

By 1974, the Advisory Board had coordinated theestablishment of specific UNS designations for over1000 metals and alloys, including steel, stainlesssteel, tool steel, superalloys, aluminum, copper,cobalt, magnesium, and nickel. These designationswere listed in the first edition of a UNS Hand-book,which was published in 1975. Each entry inthe book included the UNS designation, a brief de-scription of the alloy, the chemical composition ofthe alloy, and a list of the national specifications inwhich the alloy appeared. A typical entry from thebook is shown in Table 3.

UNS achievements over 25 years The UNS designation system has been a highly

successful venture from many standpoints. It hasprovided satisfactory solutions to the six problemareas discussed earlier in this article. Metals andAlloys in the Unified Numbering System, publishedjointly by ASTM and SAE, lists over 5000 UNS des-ignations in the recently published ninth edition. Itis also significant to note that this publication hasbeen adopted by the Department of Defense (DoD)as a replacement for MIL-HDBK-H1, Cross Index

of Chemically Equivalent Specifications and Iden-tification Code (Ferrous and Nonferrous Alloys).

The Copper Development Association, in asweeping change, replaced all of the traditionalthree-digit CDA numbers with UNS designations,and the American Welding Society now referencesUNS designations in all AWS specifications forwelding filler metal and electrodes. A large per-centage of ASTM specifications include UNS ref-erences and, for new stainless steel alloys and mostnickel alloys, UNS is the only designation listed.

Virtually all of the metals reference books pub-lished in the last 20 years have adopted UNS astheir principal indexing system, and many metal pro-ducers now reference the UNS designations in theirliterature. n

For more information: Dr. James D. Redmond, TMRStainless, 3209 McKnight East Drive, Pittsburgh, PA15327-6423; tel: 412/369-0377; fax: 412/367-2353; e-mail jredmond@tmr-inc.com

Virtuallyall of themetals referencebooks pub-lished inthe last20 yearshaveadoptedUNS astheir principalindexingsystem.

How useful did you find the informationpresented in this article?Very useful, Circle 270

Of general interest, Circle 271Not useful, Circle 272

ADVANCED MATERIALS & PROCESSES/FEBRUARY 2002 49