Table of Contents
Introduction
Steel is one of the most versatile materials used in industries like construction, automotive, and aerospace. But have you ever wondered how steel grades are named? Understanding steel naming conventions is crucial for choosing the right material for specific applications.
This guide explains domestic and international steel naming conventions so you can easily identify steel types, properties, and applications.
What Is a Steel Naming Convention?
Steel naming conventions are systems developed to classify and label different steel grades based on their composition, properties, and use. These systems help professionals differentiate between steel types and select the best material for their needs.
Domestic Steel Naming Conventions
In China, steel naming follows the GB/T 221–2008 standard, which combines Chinese pinyin, chemical element symbols, and Arabic numerals. This system covers a wide range of steel types, including carbon structural steel, alloy structural steel, stainless steel, heat-resistant steel, tool steel, and spring steel.
Carbon Structural Steel and Low-Alloy High-Strength Structural Steel
Steel in this category is named using:
- Q (Yield point)
- Numerical value (Yield point in MPa)
- Quality grade symbols
- Deoxidation method symbols
Example:
- Q235: Carbon structural steel with a yield point of 235 MPa
For low-alloy high-strength steel, the grade may also include:
- Two-digit numbers (indicating average carbon content in ten-thousandths)
- Chemical element symbols
- Symbols denoting application, characteristics, or process
Example:
- 20MnK: mining steel with 0.15%–0.26% carbon and 1.20%–1.60% manganese
High-Quality Carbon Structural Steel and Carbon Spring Steel
High-quality steel grades use:
- Two digits for carbon content (in ten-thousandths)
- Additional elements like manganese indicated with their chemical symbols
Example:
- 45: Carbon steel with 0.45% carbon
- 50Mn: Steel with higher manganese content
The method for carbon spring steel follows the same principle.
Free-Cutting Steel
Free-cutting steels are marked with Y to distinguish them from other types:
- Numbers after Y show carbon content (e.g., Y30 has 0.3% carbon)
- Additional elements like manganese indicated with their chemical symbols (e.g., Y40Mn)
Alloy Structural Steel and Alloy Spring Steel
These grades are more detailed:
- Numbers indicating average carbon or alloy content
- Alloy element symbols
- Quality grade symbols
Example:
- 40Cr: Steel containing 0.40% carbon, with chromium as the primary alloying element
Alloy spring steel follows similar naming conventions.
Stainless Steel and Heat-Resistant Steel
For these steels:
- Carbon content in thousandths
- Main alloy elements in percentages
- Microalloy elements like titanium or niobium marked by specific symbols
Example:
- 2Cr13: Stainless steel containing 0.2% carbon, with chromium as the main alloying element.
- 00Cr17Ni14Mo2: Extremely low-carbon stainless steel includes prefixes like 00 or 0
- 03Cr19Ni10: Ultra-low carbon stainless steel with ≤0.03% carbon
Tool Steel
Tool steel categories include carbon, alloy, and high-speed tool steel:
- Begins with T, followed by a number representing the carbon content in thousandths (e.g., T8 has 0.8% carbon)
- Alloy tool steels follow similar rules as alloy structural steel, omitting carbon content if ≥1%
- High-speed steels focus on alloy content (e.g., W18Cr4V for tungsten-based high-speed steel)
International Steel Naming Conventions
Different countries use unique systems for naming steel, but most combine letters and numbers to convey steel type, composition, and properties. Below are key standards used by ISO, EN, and ASTM.
International Organization for Standardization (ISO)
ISO standards use prefixes to classify steel:
- Prefix S for non-alloy structural steel (e.g., S235 for steel with ≥235 MPa yield strength)
- Letters A, B, C, D, E at the end to indicate quality grade
- Prefix E for engineering non-alloy steel (e.g., E235)
- Prefix W for weathering steel and C for heat-treated non-alloy steel (similar to China’s high-quality carbon structural steel)
- Prefix X for alloy structural steel, spring steel, and stainless steel
European Standard (EN)
EN naming conventions are similar to ISO, using a mix of letters and numbers to indicate grade and properties.
American Standard (ASTM)
ASTM systems vary for cast iron, cast steel, and forged steel:
- Cast iron: Numbers show tensile strength in 1,000 Psi
- Cast steel: Numeric codes and letter symbols (e.g., 1Q, 4QA)
- Carbon and alloy steel: Four digits, with the first two for steel type and main alloy content, and the last two for carbon content
Example:
- 1005: Carbon steel with ~0.05% carbon
- 3140: Nickel-chromium-molybdenum steel with ~0.40% carbon
For stainless steel and heat-resistant steel, ASTM assigns sequential numbers:
Example:
- 304 stainless steel: Chromium-nickel austenitic steel with >18% chromium and >8% nickel.
Conclusion
Understanding steel naming conventions helps professionals choose the right steel for their projects. Domestic systems use pinyin, chemical symbols, and numbers, while international standards like ISO, EN, and ASTM rely on letters and numbers.
Need more insights? Feel free to explore our guides to steel properties and applications.
FAQs
What does Q235 mean in steel grades?
Q represents the yield strength. 235 indicates a yield strength of 235 MPa. It is known for its good plasticity, weldability, and moderate strength, making it suitable for building structures, bridges, and machinery.
How is stainless steel named?
Stainless steel grades include carbon and main alloying elements in the name. For example, 2Cr13 means 0.2% carbon and chromium as the primary alloy.
What is the difference between ISO and ASTM steel naming?
ISO focuses on structural, engineering, and alloy steels with prefixes like S and X, while ASTM uses numeric and letter codes for steel type and properties.
Read More:
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