1. Carbon (C: ≤0.20%)
Role: Balances strength and weldability.
Effect:
Low carbon content improves weldability and reduces cold cracking risk.
Higher carbon would increase strength but harm ductility and corrosion resistance.
2. Copper (Cu: 0.25–0.55%)
Role: Primary element for weathering resistance.
Effect:
Forms a dense, adhesive rust layer (patina) that slows further corrosion.
Excess Cu may cause hot shortness during welding.
3. Chromium (Cr: 0.30–1.25%)
Role: Enhances corrosion and oxidation resistance.
Effect:
Combines with Cu to stabilize the protective patina.
Improves resistance to industrial/urban pollutants (e.g., SO₂).
4. Nickel (Ni: ≤0.65%)
Role: Boosts toughness and low-temperature performance.
Effect:
Refines grain structure, reducing brittleness in cold climates.
Supports corrosion resistance in harsh environments.
5. Phosphorus (P: ≤0.035%) & Sulfur (S: ≤0.035%)
P: Strengthens patina formation but excess can cause brittleness.
S: Minimized to avoid hot cracking during welding.
6. Silicon (Si: 0.15–0.65%) & Manganese (Mn: 0.50–1.50%)
Si: Deoxidizes steel, improves strength, and aids patina adhesion.
Mn: Enhances hardness and hardenability, balances sulfur's negative effects.
Key Performance Impacts
| Property | Dominant Elements | Effect |
|---|---|---|
| Corrosion Resistance | Cu, Cr, Ni | Forms stable rust layer. |
| Strength | C, Mn, Si | High yield (≥355 MPa) and tensile (≥490 MPa). |
| Weldability | Low C, low S | Reduces cracking risk. |
| Toughness | Ni, Mn | Good impact resistance at low temps. |
Trade-offs & Limitations
Cu/Cr Dependency: Performance drops in chloride-rich (coastal) or highly acidic environments.
Welding Precautions: Requires low-hydrogen electrodes to avoid HAZ cracking.
