A588 and A606 Type 4 are two of the most widely used weathering steel grades, and both meet the atmospheric corrosion requirements specified by ASTM.
Their alloy compositions are engineered to achieve an Atmospheric Corrosion-Resistance Index (CRI) ≥ 6.0, as defined by ASTM G101-suitable for long-term outdoor exposure without painting.
Product Availability Differences
A606 Type 4 – Weathering Steel Sheet
Thickness range: 22 Gauge (≈0.029") up to 3/16" (4.76 mm)
Forms: flat sheet, coil, corrugated roofing/siding panels
Typical hardness: 70–90 HRB
Best for forming, bending, roll-forming operations
Surface area efficiency higher → ideal for large coverage cladding
A588 – Weathering Steel Plate
Thickness range: 3/16" (4.76 mm) up to 5" (127 mm)
Forms: plate, beams, angles, channels
Used for heavy structural applications
High cross-sectional load capacity
For steel thickness ≥ 14 Gauge, dual certifications A606 Type 4 + A588 are available when chemistry meets both specifications.
Mechanical Properties Comparison
ASTM A588
Yield strength: ~50,000 psi (345 MPa)
Tensile strength: ~70,000 psi (485 MPa)
Elongation: 18–21% (depends on thickness)
Typical corrosion rate: 0.03–0.12 mm/year depending on environment
Designed for structural load-bearing applications
ASTM A606 Type 4
Yield strength: ~50,000 psi (345 MPa)
Tensile strength: ~70,000 psi (485 MPa)
Elongation: 22–26%
→ Better formability & bendability
Typical corrosion rate: 0.04–0.16 mm/year, slightly higher than A588 due to thinner typical usage
Tabular Comparison
| Feature | ASTM A588 | ASTM A606 Type 4 |
|---|---|---|
| Yield Strength | ~50,000 psi (345 MPa) | ~50,000 psi (345 MPa) |
| Tensile Strength | ~70,000 psi (485 MPa) | ~70,000 psi (485 MPa) |
| Thickness Range | 3/16"–5" | 22 GA–3/16" |
| Common Forms | Plates, beams, angles, channels | Sheets, coils, panels |
| Weather Resistance | High (Structural Grade) | Moderate–High (Sheet Grade) |
| Formability | Moderate | Excellent |
| Aesthetic Patina | Rustic, thicker patina film | Finer patina, smoother surface |
| Structural Use | Load-bearing | Non-load-bearing |
| Best For | Bridges, towers, frames | Roofing, siding, cladding |
| Cost | Medium | Lower |
Applications Supported with Data
Ideal Use Cases for A588
A588 excels in heavy-duty environments with high structural demands.
Typical corrosion savings: 50–80% lower maintenance compared to A36.
Common applications include:
Transmission towers & telecom structures
→ Service life often exceeds 40–70 years without repainting
High-rise structural frames
→ Yield strength provides 10–15% weight reduction vs regular carbon steel
Bridge plates & girders
→ Corrosion rate ≤ 0.05 mm/year in typical environments
Traffic signal structures & signposts
Industrial platforms & heavy machinery support
A588's high strength and slow corrosion rate make it suitable for areas with:
✔ freeze–thaw cycles
✔ maritime environments
✔ heavy industrial pollution
Ideal Use Cases for A606 Type 4
A606 Type 4 is optimized for sheet applications requiring bending, profiling, or roll-forming.
Typical usage data:
Roofing and siding panels often last 30–50 years without repainting
Bending performance allows 90° bends without cracking when processed correctly
Lightweight sheet reduces installation labor costs by 20–30%
Common applications include:
Architectural roofing & wall cladding
Shipping containers & storage units
Fencing, barns, agricultural buildings
Corrugated decorative panels
Outdoor signage and kiosks
Because it is easy to fabricate and cost-efficient, A606 is widely used in fast installation projects where structural strength is not the primary requirement.
