Carbon Steel: The Backbone of Global Industry — Types, Standards, and Selection Guide
2026/07/03
1. Carbon Steel Classification by Carbon Content
| Category | Carbon % | Typical Grades | Characteristics |
|---|---|---|---|
| Low Carbon | 0.05–0.30% | A36, S275, SS400, Q235 | Excellent weldability, cannot be hardened by heat treatment |
| Medium Carbon | 0.30–0.60% | 1045, C45, S45C | Balance of strength and ductility, heat-treatable |
| High Carbon | 0.60–1.00% | 1095, C95, SK5 | Highest hardness, wear resistant, difficult to weld |
2. International Standards Comparison
- ASTM (American): A36 structural, A572 HSLA, A516 pressure vessel.
- EN (European): S235-S460 series with CE marking under EN 1090.
- JIS (Japanese): SS400, SM490 — common across Asian markets.
- GB (Chinese): Q235, Q345, Q460 — world's largest steel producing nation.
3. High-Strength Low-Alloy (HSLA) Steels
Microalloyed with niobium, vanadium, and titanium, HSLA grades achieve 2-3x mild steel strength with good weldability. S355, Q345, and ASTM A572 Grade 50 are standard for modern construction.
4. Procurement Best Practices
- Specify Correct Standard: ASTM, EN, JIS, or GB with supplier-confirmed equivalents.
- Impact Testing: Charpy V-notch at design temperature for cold climate structures.
- Surface Condition: Define mill scale, rust prevention, or blasted preparation requirements.
- Dimensional Tolerances: Include thickness, flatness, and edge camber specifications.
