A grasp of metal naming conventions is essential for engineers, purchasers, and designers to navigate the global marketplace and select the right materials for their applications.
1 Introduction: The Language of Metals
Metal designation systems provide a standardized language for identifying and classifying the vast array of metals and alloys used in industry. Rather than being random strings of numbers and letters, these codes are structured to convey specific information about a material's chemical composition, mechanical properties, processing method, or a combination thereof. Understanding this language is crucial for specifying materials in procurement, ensuring quality in manufacturing, and maintaining safety in critical applications across aerospace, construction, and medical device industries.
These systems vary significantly by country and standardization body, creating a complex landscape for professionals working with international supply chains. The American Unified Numbering System (UNS) differs considerably from the Chinese GB standards or the German DIN norms. Despite this diversity, most systems follow logical patterns that, once understood, reveal their embedded information. This guide deciphers the principal methodologies behind the world's major metal designation systems, empowering you to make informed material decisions regardless of the standard being referenced.
2 Fundamental Classification of Metals
Before delving into specific naming conventions, it's essential to understand the broad categories into which metals are classified, as this often influences how they are designated.
Ferrous vs. Non-Ferrous Metals: The most fundamental division separates ferrous metals, which contain iron as their primary constituent (e.g., steels and cast irons), from non-ferrous metals, which do not have iron as their principal component (e.g., aluminum, copper, titanium, zinc). This distinction is often reflected in the structure of the designation system itself.
Pure Metals vs. Alloys: Systems further distinguish between pure metals, which are elements in their metallic form (e.g., 99.9% aluminum), and alloys, which are mixtures of two or more elements, where at least one is a metal. Alloy designations are typically more complex, encoding information about the constituent elements.
Wrought vs. Cast Products: Many systems use different prefixes or suffixes to indicate the product form. Wrought products (e.g., sheet, bar, tube) have been mechanically worked into shape, often resulting in different microstructures and properties compared to cast products, which are formed by pouring molten metal into a mold.
3 Major International Standardization Systems
Different countries and regions have developed their own standards organizations, each with its own designation philosophy. The following are the most influential systems encountered in global trade and engineering.
3.1 American System (SAE/AISI, ASTM, UNS, AMS)
The American system is not a single standard but an ecosystem of complementary designations.
SAE/AISI Steel Designations: For decades, the Society of Automotive Engineers (SAE) and American Iron and Steel Institute (AISI) systems were the primary methods for designating carbon and alloy steels in the U.S. These typically use a four-digit code where the first two digits indicate the alloy family (e.g., "10" for carbon steel, "41" for chromium-molybdenum steel) and the last two digits represent the nominal carbon content in hundredths of a percent. A "B" inserted between the second and third digits (e.g., 10B46) indicates the addition of boron for improved hardenability .
Unified Numbering System (UNS): The UNS was established to provide a cross-referencing database that minimizes confusion between different numbering systems. A UNS number is not a specification itself but a unique identifier that links to a specific composition in other standards. It typically consists of a single letter followed by five digits (e.g., G10400 for a carbon steel, C36000 for a copper alloy). The letter indicates the metal family: 'G' for carbon and alloy steels, 'A' for aluminum, 'C' for copper, 'S' for stainless steels, and 'T' for tool steels, among others .
ASTM and AMS Designations: The American Society for Testing and Materials (ASTM) and Aerospace Material Specifications (AMS) often use descriptive codes that may reference a material's properties or application rather than a strict chemical formula. An "ASTM A36" steel, for instance, is defined by its mechanical properties (primarily a minimum yield strength of 36 ksi), while "AMS 4911" specifies a titanium alloy sheet product form.
3.2 Chinese National Standards (GB)
The Chinese GB standards, administered by the Standardization Administration of China (SAC), employ a systematic approach using Chinese Pinyin letters and numbers.
Steels: For steels, prefixes often denote the use or process route. 'Q' is used for steels where the primary designation is based on Yield Strength . Alloy structural steels may start with numbers indicating the carbon content, followed by chemical symbols of the primary alloying elements and their percentages .
Non-Ferrous Metals: The system uses Pinyin letters derived from the Chinese name of the base metal .
Aluminum and its alloys are designated with 'L' (from "Lü").
Copper and its alloys use 'T' (from "Tong").
Subsequent letters and numbers then specify the alloy type, series, and specific grade. For example, in 'LF', 'L' stands for aluminum, and 'F' ("Fang") indicates it is a anti-rust alloy . Cast aluminum alloys use 'ZL' for "Zhu Lü" (cast aluminum) .
3.3 European Systems (DIN, EN)
German DIN: The Deutsches Institut für Normung (DIN) standards are known for their detailed and descriptive designations. For steels, the system often uses a combination of letters and numbers where the number represents the minimum tensile strength (e.g., St42 for a steel with ≈420 MPa tensile strength) or a code for the chemical composition (e.g., C15E for a carbon steel with ~0.15% C, "E" for case-hardening). The alphanumeric codes are highly specific, detailing alloying elements and their approximate quantities .
European Norm (EN): The EN system is replacing many national standards within the European Union, aiming for harmonization. It often adopts a principle similar to the U.S. UNS system, acting as a superset that incorporates and cross-references older national standards like DIN. EN standards have their own numbering scheme but frequently maintain a link to the legacy designation for clarity.
3.4 Japanese Industrial Standards (JIS)
The Japanese Industrial Standards (JIS) system often uses single or double letters to denote the material category, followed by numbers. For steels, the prefix 'S' denotes "Steel." This is followed by additional letters for the specific type: 'S-C' for carbon steel for structures, 'S-K' for carbon tool steel, 'SUS' for stainless steel, and 'SUH' for heat-resistant steel. The numbers that follow typically indicate tensile strength, a serial number, or, in the case of stainless steels, often correspond to the AISI type (e.g., SUS304 is broadly equivalent to AISI 304) .
3.5 International Organization for Standardization (ISO)
The International Organization for Standardization (ISO) aims to create globally harmonized standards. Its designations often seek to bridge the gaps between the major national systems. For steels, ISO 683 series, for example, uses a system based on chemical composition and heat treatment, with designations that are logical but not always intuitive without a reference table. The ISO system's strength lies in its role as a neutral reference point for international contracts and technical documentation .
4 Decoding Specific Material Categories
The logic of designation systems becomes clearer when applied to specific material families.
4.1 Steel and Iron-Based Alloys
Steel naming conventions are among the most varied, often blending information about composition, mechanical properties, and application.
| Prefix/Symbol | Standard System | Typical Meaning/Application |
| 10XX, 41XX, etc. | SAE/AISI | A four-digit code where the first two digits indicate the alloy series and the last two the carbon content. |
| Q + Yield Strength | GB (China) | Steel where the primary designation is based on Yield Strength (e.g., Q235 has a yield strength of 235 MPa) . |
| S + Letter | JIS (Japan) | S' for Steel, followed by a letter for category (e.g., 'S-C' for carbon steel for structures) . |
| St + Number | DIN (Germany) | St for "Stahl" (steel), with the number indicating minimum tensile strength (e.g., St42) . |
| G | UNS (USA) | Letter prefix for carbon and alloy steels in the UNS system. |
| AISI 304 / SUS304 | AISI (USA) / JIS (Japan) | A common stainless steel grade; the "300-series" denotes austenitic structure. |
Stainless Steels: Most systems classify stainless steels into families like austenitic (200 and 300 series), ferritic (400 series), and martensitic (400 series). The widely used AISI 3-digit system (e.g., 304, 316) is referenced, either directly or indirectly, in many other national standards like JIS (as SUS304) .
Tool Steels: These are often designated by their application and alloy content. The AISI system uses letters like 'A' for air-hardening, 'O' for oil-hardening, 'W' for water-hardening, and 'H' for hot-work tool steels, followed by a sequence number.
4.2 Aluminum and Aluminum Alloys
Aluminum designations are predominantly governed by a four-digit system developed by The Aluminum Association, which has been adopted widely, including in the U.S. UNS and as a basis for other international standards.
Wrought Alloys:
1xxx Series: 99.00% minimum aluminum (e.g., 1050, 1100).
2xxx Series: Copper is the principal alloying element (e.g., 2024, used in aircraft).
3xxx Series: Manganese is the principal alloying element (e.g., 3003, for general-purpose use).
4xxx Series: Silicon is the principal alloying element (e.g., 4043, used for welding wire).
5xxx Series: Magnesium is the principal alloying element (e.g., 5052, 5083 for marine applications).
6xxx Series: Magnesium and silicon (for forming Mg2Si); heat-treatable (e.g., 6061, 6063 for extrusions).
7xxx Series: Zinc is the principal alloying element (e.g., 7075, a high-strength aerospace alloy).
Cast Alloys: Use a similar 3-digit system plus a decimal (e.g., 356.0, A380.0). The first digit indicates the alloy group.
Temper Designation: A crucial part of an aluminum designation is the temper, which indicates the material's condition. It follows the alloy number and is separated by a hyphen (e.g., 6061-T6). Common tempers include 'O' for annealed, 'F' for as-fabricated, 'H' for strain-hardened, and 'T' for heat-treated.
4.3 Copper and Copper Alloys
Copper alloys are primarily designated using the UNS system, which groups them by their primary alloying elements.
Copper (C1xxxx): Unalloyed coppers with high electrical conductivity.
High-Copper Alloys (C16xxx-C19xxx): Alloys with small additions of other elements.
Brasses (C2xxxx to C4xxxx): Alloys of copper and zinc. The UNS number often relates to the older, more familiar names like "Cartridge Brass" (C26000) or "Naval Brass" (C46400).
Bronzes (C5xxxx to C6xxxx): Historically copper-tin alloys, but the term now broadly encompasses copper alloys with elements other than zinc as the primary alloy, such as aluminum bronzes (C6xxxx), silicon bronzes (C64xxx), and phosphor bronzes (C5xxxx).
Copper-Nickels (C7xxxx): Alloys of copper and nickel, known for excellent corrosion resistance (e.g., C71500).
5 Practical Applications and Cross-Standard Usage
Navigating between different international standards is a common challenge.
Using Cross-Reference Tables and Handbooks: When a drawing or specification calls for a material under an unfamiliar standard, the first step is to consult a reliable cross-reference table or handbook . These resources list equivalent or similar grades across different standards. It is critical to understand that "equivalent" does not always mean "identical"; there can be subtle but important differences in permitted impurity levels or processing requirements.
Critical Considerations for Material Selection and Substitution: Substituting a material based solely on a chemical composition match from a cross-reference table can be risky. A comprehensive evaluation must consider:
Mechanical Property Requirements: Verify that the substitute meets all specified strength, ductility, and toughness values.
Heat Treatment Response: Different processing routes can lead to different microstructures and performance.
Corrosion Resistance: Minor differences in composition can significantly impact corrosion behavior.
Weldability and Formability: These processing characteristics are not always fully captured in a basic grade designation.
Applicable Specifications and Certifications: In regulated industries (aerospace, medical, nuclear), a material must often be sourced and certified to a specific standard, not just a "similar" one.
