Accurate interpretation of steel grades is crucial for ensuring material compliance and project safety in structural steel design, procurement, and construction. While the steel grading systems of both countries share connections, they also exhibit distinct differences. A thorough understanding of these distinctions is vital for industry professionals.
Chinese Steel Designations
Chinese steel designations follow a core format of “Pinyin letter + chemical element symbol + Arabic numeral,” with each character representing specific material properties. Below is a breakdown by common steel types:
1. Carbon Structural Steel/Low-Alloy High-Strength Structural Steel (Most Common)
Core Format: Q + Yield Point Value + Quality Grade Symbol + Deoxidation Method Symbol
• Q: Derived from the initial letter of “yield point” in pinyin (Qu Fu Dian), signifying yield strength as the primary performance indicator.
• Numerical value: Directly denotes the yield point (unit: MPa). For example, Q235 indicates a yield point ≥235 MPa, while Q345 denotes ≥345 MPa.
• Quality Grade Symbol: Classified into five grades (A, B, C, D, E) corresponding to impact toughness requirements from low to high (Grade A requires no impact test; Grade E requires -40°C low-temperature impact test). For example, Q345D denotes low-alloy steel with a yield strength of 345 MPa and Grade D quality.
• Deoxidation method symbols: F (free-running steel), b (semi-killed steel), Z (killed steel), TZ (special killed steel). Killed steel offers superior quality to free-running steel. Engineering practice commonly uses Z or TZ (may be omitted). For example, Q235AF denotes free-running steel, while Q235B denotes semi-killed steel (default).
2. High-Quality Carbon Structural Steel
Core Format: Two-digit number + (Mn)
• Two-digit number: Represents average carbon content (expressed in parts per ten thousand), e.g., 45 steel indicates carbon content ≈ 0.45%, 20 steel indicates carbon content ≈ 0.20%.
• Mn: Indicates high manganese content (>0.7%). For example, 50Mn denotes a high-manganese carbon steel with 0.50% carbon.
3. Alloy Structural Steel
Core format: Two-digit number + alloy element symbol + number + (other alloy element symbols + numbers)
• First two digits: Average carbon content (per ten thousand), e.g., “40” in 40Cr represents carbon content ≈ 0.40%.
• Alloy element symbols: Commonly Cr (chromium), Mn (manganese), Si (silicon), Ni (nickel), Mo (molybdenum), etc., representing primary alloying elements.
• Digit following element: Indicates the alloy element's average content (in percent). Content <1.5% omits a digit; 1.5%-2.49% denotes “2”, and so on. For example, in 35CrMo, no number follows “Cr” (content ≈ 1%), and no number follows “Mo” (content ≈ 0.2%). This denotes an alloy structural steel with 0.35% carbon, containing chromium and molybdenum.
4. Stainless Steel/Heat-Resistant Steel
Core Format: Number + Alloy Element Symbol + Number + (Other Elements)
• Leading number: Represents average carbon content (in parts per thousand), e.g., “2” in 2Cr13 indicates carbon content ≈0.2%, “0” in 0Cr18Ni9 indicates carbon content ≤0.08%.
• Alloy element symbol + number: Elements like Cr (chromium) or Ni (nickel) followed by a number denote average element content (in percent). For example, 1Cr18Ni9 indicates an austenitic stainless steel with 0.1% carbon, 18% chromium, and 9% nickel.
5. Carbon Tool Steel
Core format: T + number
• T: Derived from the initial letter of “carbon” in pinyin (Tan), representing carbon tool steel.
• Number: Average carbon content (expressed as a percentage), e.g., T8 denotes carbon content ≈0.8%, T12 denotes carbon content ≈1.2%.
U.S. Steel Designations: ASTM/SAE System
U.S. steel designations primarily follow ASTM (American Society for Testing and Materials) and SAE (Society of Automotive Engineers) standards. The core format consists of a “numeric combination + letter suffix,” emphasizing steel grade classification and carbon content identification.
1. Carbon Steel and Alloy Structural Steel (SAE/ASTM Common)
Core Format: Four-digit number + (letter suffix)
• First two digits: Denote steel type and primary alloying elements, serving as the “classification code.” Common correspondences include:
◦10XX: Carbon steel (no alloying elements), e.g., 1008, 1045.
◦15XX: High-manganese carbon steel (manganese content 1.00%-1.65%), e.g., 1524.
◦41XX: Chromium-molybdenum steel (chromium 0.50%-0.90%, molybdenum 0.12%-0.20%), e.g., 4140.
◦43XX: Nickel-Chromium-Molybdenum Steel (nickel 1.65%-2.00%, chromium 0.40%-0.60%), e.g., 4340.
◦30XX: Nickel-Chromium Steel (containing 2.00%-2.50% Ni, 0.70%-1.00% Cr), e.g., 3040.
• Last two digits: Represent average carbon content (in parts per ten thousand), e.g., 1045 indicates carbon content ≈ 0.45%, 4140 indicates carbon content ≈ 0.40%.
• Letter suffixes: Provide supplementary material properties, commonly including:
◦ B: Boron-containing steel (enhances hardenability), e.g., 10B38.
◦ L: Lead-containing steel (facilitates machinability), e.g., 12L14.
◦ H: Guaranteed hardenability steel, e.g., 4140H.
2. Stainless Steel (Primarily ASTM Standards)
Core Format: Three-digit number (+ letter)
• Number: Represents a “sequence number” corresponding to fixed composition and properties. Memorization is sufficient; calculation is unnecessary. Common industry grades include:
◦304: 18%-20% chromium, 8%-10.5% nickel, austenitic stainless steel (most common, corrosion resistant).
◦316: Adds 2%-3% molybdenum to 304, offering superior acid/alkali resistance and high-temperature performance.
◦430: 16%-18% chromium, ferritic stainless steel (nickel-free, low cost, prone to rust).
◦410: 11.5%-13.5% chromium, martensitic stainless steel (hardenable, high hardness).
• Letter suffixes: For example, the “L” in 304L denotes low carbon (carbon ≤0.03%), reducing intergranular corrosion during welding; the “H” in 304H indicates high carbon (carbon 0.04%-0.10%), enhancing high-temperature strength.
Core Differences Between Chinese and American Grade Designations
1. Different Naming Logics
China's naming rules comprehensively consider yield strength, carbon content, alloy elements, etc., using combinations of letters, numbers, and element symbols to precisely convey steel properties, facilitating memorization and understanding. The U.S. primarily relies on numerical sequences to denote steel grades and compositions, which is concise but slightly more challenging for non-specialists to interpret.
2. Details in Alloy Element Representation
China provides detailed representation of alloy elements, specifying labeling methods based on different content ranges; While the U.S. also indicates alloy content, its notation for trace elements differs from China's practices.
3. Application Preference Differences
Due to varying industry standards and construction practices, China and the U.S. exhibit distinct preferences for specific steel grades in certain applications. For example, in structural steel construction, China commonly uses low-alloy high-strength structural steels like Q345; the U.S. may select corresponding steels based on ASTM standards.
Post time: Oct-27-2025
