ASTM A588 Grade B is the most widely specified weathering steel grade for North American structural projects, available as plate, sheet, coil and structural shapes. Its alloy system of copper, chromium, nickel and phosphorus forms a dense patina in atmospheric service, which is why bridges, facades and heavy machinery frames can run for decades without painting.
Key Takeaways
Plate and sheet: 1.5-60 mm thick; coil: 0.5-16 mm thick, 300-2000 mm wide.
Minimum yield strength 345 MPa; minimum tensile strength 485 MPa for plates.
Grade B carries higher copper and chromium than Grade A, giving stronger corrosion resistance.
Self-protecting patina eliminates painting in most atmospheric applications.
Available Forms and Dimensions
Corten steel coil is supplied at 0.5-16 mm thickness and 300-2000 mm width for roll-forming and cladding lines. Plate and sheet run 1.5-60 mm thick, with common widths of 1000, 1175, 1220, 1250, 1500 and 2000 mm, and lengths of 2000, 2500, 3000, 5800 and 6000 mm, or to project specification. Confirm the exact range with the mill before ordering structural sizes.
Chemical Composition
A588 Grade B is balanced for weathering: carbon up to 0.20%, manganese 0.75-1.35%, phosphorus up to 0.04%, sulfur up to 0.05%, silicon 0.15-0.50%, copper 0.20-0.40%, nickel up to 0.50%, chromium 0.40-0.70% and vanadium 0.01-0.10%. Compared with Grade A, Grade B carries higher copper and chromium, which gives it stronger corrosion resistance in the same atmosphere.
Mechanical Properties
For plates up to 100 mm, minimum tensile strength is 485 MPa and minimum yield strength is 345 MPa, with minimum elongation of 21%. For plates 100-125 mm, tensile is 460 MPa and yield 315 MPa; for 125-200 mm, tensile is 435 MPa and yield 290 MPa. Structural shapes maintain the 485/345 MPa combination. Request the mill test certificate to confirm the values for the required thickness band.
Corrosion Resistance and Key Characteristics
Exposed to the atmosphere, the steel forms a protective rust-like oxide layer that slows further corrosion and eliminates painting in most applications. The minimum yield strength of 345 MPa applies to plates up to 100 mm, and the alloy additions of copper, chromium, nickel and phosphorus drive the weathering behavior that ordinary carbon steel lacks.
Typical Applications
A588 Grade B is intended for welded, riveted or bolted construction: bridges and overpasses, building facades and structural frames, railway carriages and containers, mining equipment, cranes and construction vehicles, and landscape architecture such as park corridors, retaining walls and sculptures where the unique color and texture are design features.
Frequently Asked Questions
Q: What thickness ranges are available for A588 Grade B?
Plate and sheet run 1.5-60 mm thick, while coil is supplied at 0.5-16 mm thick and 300-2000 mm wide for roll-forming and cladding lines.
Q: What are the minimum mechanical properties of A588 Grade B plate?
For plates up to 100 mm the minimum yield is 345 MPa, tensile 485 MPa and elongation 21%; the limits step down to 315/460 MPa for 100-125 mm and 290/435 MPa for 125-200 mm.
Q: Is A588 Grade B different from Grade A?
Yes. Grade B carries higher copper and chromium, which gives it stronger corrosion resistance in the same atmosphere.
Q: What chemical composition defines A588 Grade B?
Carbon up to 0.20%, manganese 0.75-1.35%, silicon 0.15-0.50%, copper 0.20-0.40%, chromium 0.40-0.70%, nickel up to 0.50%, phosphorus up to 0.04% and vanadium 0.01-0.10%.
Q: What are the typical applications for A588 Grade B sheet and plate?
Bridges, building facades, heavy machinery frames and other long-life outdoor structures, because the self-protecting patina allows decades of service without painting.
Q: What sizes should be confirmed before ordering?
Common widths are 1000, 1175, 1220, 1250, 1500 and 2000 mm, and common lengths 2000, 2500, 3000, 5800 and 6000 mm; the exact range should be confirmed with the mill before ordering structural sizes.
