ASTM A588 Grade B and Corten A are both high-strength, low-alloy (HSLA) weathering steels designed for enhanced atmospheric corrosion resistance. They form a protective rust-like patina (oxide layer) when exposed to weather, reducing the need for painting and extending service life in outdoor environments.
Corten A (a trademarked name from U.S. Steel, often equivalent to ASTM A588 Grade A or EN 10025-5 S355J0WP) is commonly used for aesthetic or moderate-load applications like facades, sculptures, and flues. ASTM A588 Grade B, part of the A588 family, is more tailored for structural uses requiring better toughness, such as bridges and heavy frameworks, with subtle chemical tweaks for improved performance in varied conditions.
While mechanically similar, key differences lie in chemical composition (e.g., phosphorus and alloying elements), which affect corrosion behavior, weldability, and low-temperature toughness. A588 Grade B is not a direct equivalent to Corten A but serves as a close alternative with potentially superior impact resistance due to higher manganese and nickel.
Chemical Composition Comparison
|
Element |
Corten A |
ASTM A588 Grade A |
ASTM A588 Grade B |
|---|---|---|---|
|
Carbon (C) |
0.12% max |
0.19% max |
0.20% max |
|
Manganese (Mn) |
0.20–0.50% |
0.80–1.25% |
0.75–1.35% |
|
Phosphorus (P) |
0.07–0.15% (max 0.15%) |
0.030% max |
0.030% max |
|
Sulfur (S) |
0.030% max |
0.030% max |
0.030% max |
|
Silicon (Si) |
0.25–0.75% |
0.30–0.65% |
0.15–0.50% |
|
Nickel (Ni) |
0.65% max |
0.40% max |
0.50% max |
|
Chromium (Cr) |
0.50–1.25% |
0.40–0.65% |
0.40–0.70% |
|
Copper (Cu) |
0.25–0.55% |
0.25–0.40% |
0.20–0.40% |
|
Vanadium (V) |
Not specified |
0.02–0.10% |
0.01–0.10% |
|
Aluminum (Al) |
0.015–0.06% |
Not specified |
Not specified |
Mechanical Properties Comparison
|
Property |
Corten A |
ASTM A588 Grade A/B (both grades identical) |
|---|---|---|
|
Yield Strength |
345 MPa (50 ksi) min |
345 MPa (50 ksi) min (decreases to 290 MPa/42 ksi over 5–8 inches) |
|
Tensile Strength |
485 MPa (70 ksi) min |
485 MPa (70 ksi) min (decreases to 435 MPa/63 ksi over 5–8 inches) |
|
Elongation (min, 2") |
20% |
21% |
|
Thickness Range |
2–12 mm (strips); 6–12 mm (plates) |
Up to 200 mm (plates) |
Applications and Suitability
Corten A: Ideal for non-structural or aesthetic uses (e.g., building facades, railway cars, sculptures) where visual rust patina is desired. Higher P suits decorative or flue applications but limits heavy-load use.
A588 Grade B: Preferred for load-bearing structures (e.g., bridges, transmission towers, shipbuilding) needing better cold-weather toughness and weldability. It's more versatile for thicker sections and industrial exposure.
Similarities: Both provide 4–8x better corrosion resistance than plain carbon steel (e.g., A36) in rural/moderate atmospheres; avoid marine or high-pollution areas without coatings.
Welding/Fabrication: Preheat recommended (100–150°C) for both; use low-hydrogen fillers. A588 Grade B is easier to bend/form due to lower P.
Cost/Availability: Comparable pricing (~20–30% more than mild steel); A588 Grade B may be more readily available in the U.S. for structural specs.
