Definition of Corrosion
Corrosion is the process by which a material deteriorates due to chemical or electrochemical reactions between the base material and its environment.
Simply put, exposed surfaces may react with air, moisture, saltwater, and other substances to form by-products that degrade the material's critical properties. However, these reactions can also be utilized to design suitable corrosion-resistant steels.
When designing corrosion-resistant steels, there are two main options:
- Weathering steel alloys (such as Corten A/B)
- Stainless steel grades
Chemical Composition Comparison
| Element | Corten A/B (%) | Stainless Steel 304 (%) | Stainless Steel 316 (%) |
|---|---|---|---|
| Carbon (C) | 0.12 max | 0.08 max | 0.08 max |
| Manganese (Mn) | 0.25–1.35 | 2.0 max | 2.0 max |
| Phosphorus (P) | 0.07 max | 0.045 max | 0.045 max |
| Sulfur (S) | 0.05 max | 0.03 max | 0.03 max |
| Silicon (Si) | 0.25–0.75 | 1.0 max | 1.0 max |
| Chromium (Cr) | 0.50–1.25 | 18–20 | 16–18 |
| Nickel (Ni) | 0.65 | 8–10.5 | 10–14 |
| Copper (Cu) | 0.25–0.55 | - | - |
| Molybdenum (Mo) | - | - |
2–3 |
Corten A/B Weathering Steel
Corten is the generic trademark for weathering steels, characterized by a rust-orange appearance. Weathering steel is primarily used in heavy-duty industrial applications to reduce the need for costly surface coatings. Alloying elements such as copper, chromium, and nickel form a hardened protective layer on the surface, which continuously regenerates when exposed to air pollutants, humidity, and rainfall.
Advantages:
Excellent combination of corrosion resistance and tensile strength, making it one of the most durable corrosion-resistant steels.
Unique appearance suitable for architectural decoration and outdoor art projects.
Disadvantages:
Weathering rate can be difficult to predict in rural environments.
Not suitable for applications requiring resistance to aggressive chemicals or high hygiene standards.
Applications:
Bridges, ship plates, building cladding, art installations, heavy-duty transport equipment, etc.
Stainless Steel
Stainless steel is renowned for its high versatility. The main component is chromium (>10%) with low carbon content. A thin, invisible passivation layer forms on the surface, providing resistance to acidic corrosion, galvanic corrosion, and other corrosive conditions.
Advantages:
Provides broad-spectrum corrosion protection, with a variety of grades available for different applications.
Passivation layer is self-repairing, preventing localized damage from spreading.
Surface remains stable over time and does not flake.
Disadvantages:
Hardness and wear resistance are lower than Corten steel.
Appearance is less distinctive compared to weathering steel (mainly subjective).
Applications:
Food equipment, chemical equipment, medical devices, architectural decoration, marine structures, etc.
