Development of the UNIFIED NUMBERING This article reviews the Unified Numbering System for Metals and Alloys—what it is, why it was SYSTEM conceived, and how it was developed. Harold M. Cobb* Organization of UNS Metallurgical Consultant Kennett Square, Pennsylvania The UNS, jointly sponsored by the American Society for Testing and Materials (ASTM) and the Society of Automotive Engineers (SAE), is operated in accordance with ASTM E527/SAE J esignation systems for metals and alloys 1086, Recommended Practice for Numbering in the United States have traditionally been Metals and Alloys. The organization for admin- those established by various groups, in- istering the UNS consists of an advisory board, Dcluding metal producers; trade associa- three number-assigning offices, a corps of vol- tions such as the Aluminum Association (AA), the unteer consultants, and staffs at ASTM and SAE. American Iron & Steel Institute (AISI), and the Dr. James D. Redmond is the current chairman Copper Development Association (CDA); profes- of the UNS Advisory Board. sional societies such as the American Society for Testing and Materials (ASTM), the American *Life member of ASM International Welding Society (AWS), and the Society of Auto- ferent numbers, three digits for AISI and five digits for motive Engineers (SAE); and the U. S. government. SAE. By the 1960s, it was becoming increasingly ap- • Discontinued numbers: The AISI decided to dis- parent that the traditional approach to the designa- continue the practice of designating numbers for tion of metals left some problem areas that could steels, and this was a particular problem with re- not be satisfactorily solved. The following list of some gard to the assignment of designations to new stain- of these problems should make it clear that a case less steels. ASTM was attempting to fill the gap by could be made for developing an entirely new metals issuing a new series of numbers for proprietary stain- designation system: less steels (e.g., XM-1, XM-2, XM-3, etc.) • Trade names: Many alloys were known only by • Outmoded systems: CDA’s three-digit system trade names in cases where no central organiza- for the numbering of copper alloys was outmoded, tion assigned numbers. However, the technical so- and a new system was being considered. cieties had policies prohibiting the use of trade • Variety of designations: The U.S. government names in their specifications. Therefore, it became often had metal designations that differed from the practice, for nickel alloys, to list the principal al- those of other specification-writing bodies. loying elements as the designation. For example, a well-known nickel alloy was given the designation A new numbering system “Nickel-chromium-cobalt-molybdenum alloy,” a des- Because of these problems, in 1967 the Amer- ignation which was not particularly meaningful to ican Society for Testing and Materials (ASTM) and most readers. the Society of Automotive Engineers (SAE) began • Same number for different alloys: It was not un- to explore the possibility of developing a new num- usual for the various trade associations to assign bering system for metals that would address the dif- the same number to different alloys. For example, ficulties described above and provide numbers for all Alloy 205 could be either a copper alloy, a nickel alloys. alloy, or a type of stainless steel. The U.S. Army was especially interested in this • Different numbers for the same alloy: The AISI subject, and in May 1969 the Army Materials and and SAE designated the same stainless steels by Mechanics Research Center (AMMRC) issued a dif-contract to the SAE to conduct a “Feasibility Study of

ADVANCED MATERIALS & PROCESSES/FEBRUARY 2002 47 Table 1— Primary series of UNS numbers UNS series Metal group UNS series Metal group Axxxxx Aluminum and aluminum alloys Lxxxxx Low melting metals and alloys Cxxxxx Copper and copper alloys Mxxxxx Miscellaneous nonferrous metals & alloys Dxxxxx Steels—designated by mechanical property Nxxxxx Nickel and nickel alloys Exxxxx Rare earth and rare earth-like alloys Pxxxxx Precious metal and alloys Fxxxxx Cast irons Rxxxxx Reactive and refractory metals and alloys Gxxxxx AISI and SAE carbon and alloy steels Sxxxxx Stainless steels, valve steels, superalloys Hxxxxx AISI H-steels Txxxxx Tool steels Jxxxxx Cast steels Wxxxxx Welding filler metals Kxxxxx Miscellaneous steels and ferrous alloys Zxxxxx Zinc and zinc alloys Table 2—Examples of UNS designations the eighteen-month feasibility study expressed grave doubts about the possibility of establishing an overall UNS Traditional designation numbering system, but others thought it was worth A03190 AA 319.0 (Aluminum alloy casting) exploring. The major trade associations concerned A92024 AA 2024 (Wrought aluminum alloy) with metals numbering systems were also consulted, C26200 CDA 262 (Cartridge brass) including the Aluminum Association, the American G12144 AISI 12L14 (Leaded alloy steel) Iron & Steel Institute, the Copper Development As- G41300 AISI 4130 (Alloy steel) sociation, and the Steel Founders’ Society of K93600 Invar (36% nickel alloy steel) America (SFSA). It was recognized at the outset L13700 Alloy Sn 70 (Tin-lead solder) that any new system could be successful only if N06007 Nickel-chromium alloy (Hastelloy G) these organizations were in general agreement with N06625 Alloy 625 (Nickel-chromium-molybdenum-columbium the concept. alloy) In January 1971, the study was completed and R58210 Alloy 21 (Titanium alloy) a report was submitted to the U.S. Army stating that S30452 AISI 304N (Stainless steel, high nitrogen) it had been determined that a unified numbering S32550 Ferralium 255 (Duplex stainless steel) systems for metals was feasible and desirable. The T30108 AISI A-8 (Tool steel) report included a general proposal of how such a W30710 AWS E307 (Stainless steel electrode) system could be established to provide a coherent Z33520 Alloy AG40A (Zinc alloy) designation system for all current and future metals and alloys. a Unified Numbering System for Metals and Alloys.” In April 1972, ASTM and SAE established an Ad- This project was jointly sponsored by ASTM and visory Board to further develop and refine the pro- SAE, and a committee was appointed to conduct posed numbering system The Advisory Board con- the study. The committee was chaired by Norman L. sisted of the following members: Mochel, a past president of ASTM, and consisted Chairman: Bruce A. Smith, General Motors of the following members: Engineering Staff Herbert F. Campbell, Army Materials and Secretaries: Harold M. Cobb, ASTM Staff Mechanics Research Center R. Thomas Northrup, SAE Staff Harold M. Cobb, American Society for Testing Members: and Materials John Artman, Defense Industrial Supply Center Alvin G. Cook, Allegheny Ludlum Steel Corp. Lawrence H. Bennett, National Bureau of Henry B. Fernald, Technical Consultant Standards Muir L. Frey, Engineering Consultant Alvin G. Cook, Allegheny Ludlum Steel Corp. S. T. Main, Grumman Aircraft Corp. Henry B. Fernald, Jr., Technical consultant Norman L. Mochel, Engineering Consultant John Gadbut, International Nickel Co. R. Thomas Northrup, Society of Automotive Joseph M. Engel, Republic Steel Corp. Engineers (representing AISI) Bruce A. Smith, General Motors Engineering Staff W. Stuart Lyman, Copper Development Harry H. Stout, Phelps Dodge Copper Products Association Corp. Robert E. Lyons, Federal Supply Service Norman L. Mochel, Metallurgical Consultant Development of the UNS Edward F. Parker, General Electric Co. Some individuals consulted during the course of Richard R. Senz, The Aluminum Co. of America Tabel 3 — A typical entry from metals and alloys in the Unified Numbering System Nickel 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.) of Chemically Equivalent Specifications and Iden- Whitney Snyder, American Motors Corp. tification Code (Ferrous and Nonferrous Alloys). Rudolph Zillman, Steel Founders’ Society The Copper Development Association, in a Virtually of America sweeping change, replaced all of the traditional This Board decided that the official name of the three-digit CDA numbers with UNS designations, all of the new all-encompassing system would be the “Uni- and the American Welding Society now references metals fied Numbering System for Metals (UNS).” The UNS designations in all AWS specifications for reference major guiding principles of the system would be as welding filler metal and electrodes. A large per- follows: centage of ASTM specifications include UNS ref- books • Each designation for a metal or alloy should per- erences and, for new stainless steel alloys and most pub- tain to a specific metal or alloy as determined by its nickel alloys, UNS is the only designation listed. lished in unique chemical composition, or to its Virtually all of the metals reference books pub- mechanical properties or physical characteristics lished in the last 20 years have adopted UNS as the last when these are the primary defining criteria and the their principal indexing system, and many metal pro- 20 years chemical composition is secondary or not ducers now reference the UNS designations in their have significant. literature. n • For ease of recognition, the numbers assigned adopted should incorporate numbers from existing num- UNS as bering systems whenever possible. For more information: Dr. James D. Redmond, TMR • The numbering system should be designed to Stainless, 3209 McKnight East Drive, Pittsburgh, PA their accommodate current metals and alloys, and to an- 15327-6423; tel: 412/369-0377; fax: 412/367-2353; e- principal mail [email protected] ticipate the need to provide numbers for new alloys indexing for the foreseeable future. • The system should be ideally suited for com- system. puter use and for the general indexing of metals and alloys. How useful did you find the information presented in this article? Description of the system Very useful, Circle 270 In March 1974, the UNS Advisory Board com- Of general interest, Circle 271 pleted the “SAE/ASTM Recommended Practice for Not useful, Circle 272 Numbering Metals and Alloys.” This established eighteen 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 were 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 desig- nations 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 Hand- book,which was published in 1975. Each entry in the book included the UNS designation, a brief de- scription 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 Table 3.

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 des- ignations 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

ADVANCED MATERIALS & PROCESSES/FEBRUARY 2002 49