1. Chemical Composition (Typical)
| Element | Content (%) | Role in Corrosion Resistance |
|---|---|---|
| C (Carbon) | ≤ 0.10% | Maintains weldability, reduces brittleness |
| Si (Silicon) | 0.20–0.50% | Strengthens rust layer stability |
| Mn (Manganese) | 0.20–0.50% | Enhances strength, fixes sulfur |
| P (Phosphorus) | 0.07–0.12% | Critical for protective patina formation |
| S (Sulfur) | ≤ 0.035% | Minimized to avoid brittleness |
| Cu (Copper) | 0.25–0.45% | Key element for rust adhesion & corrosion resistance |
| Cr (Chromium) | 0.30–0.65% | Improves oxidation resistance |
| Ni (Nickel) | 0.25–0.50% | Enhances toughness & corrosion resistance |
2. Key Properties
Corrosion Resistance:
Forms a dense, self-healing rust layer (patina) when exposed to weather.
2–8x more resistant than plain carbon steel in industrial/marine environments.
Mechanical Properties:
Yield Strength: ≥ 345 MPa (similar to ASTM A588).
Tensile Strength: 470–630 MPa.
Elongation: ≥ 22%.
Weldability:
Good (low carbon & controlled P/S content).
Use low-hydrogen electrodes (E7018-W) for best results.
3. Equivalent Grades
| Standard | Equivalent Grade | Comparison |
|---|---|---|
| China (GB) | Q355NH | Nearly identical, slightly different Cr/Ni balance |
| ASTM (USA) | A588 Grade K | Very close in composition & performance |
| EN (Europe) | S355J0WP / S355J2WP | Similar weathering properties |
| JIS (Japan) | SPA-H (JIS G3125) | Comparable Cu-P-Cr-Ni system |
4. Applications
Bridges & Highway Structures (resists de-icing salts).
Shipping Containers & Railway Cars (long-term durability).
Architectural Facades (aesthetic rust appearance).
Transmission Towers & Offshore Platforms (marine resistance).
5. Advantages Over Plain Carbon Steel
✔ Lower maintenance (no painting required after patina forms).
✔ Longer service life in harsh environments.
✔ Cost-effective vs. stainless steel for outdoor use.
6. Limitations
Not for submerged/constant wet environments (better suited for atmospheric exposure).
Initial rust runoff may stain surfaces (requires drainage planning).
