What is ASTM A588 Gr.A / Gr.B Weathering Steel Plate?
Core Standard Definition
ASTM A588/A588M‑19: Standard specification for high‑strength low‑alloy atmospheric‑corrosion‑resistant steel, primarily used for commercial buildings, landscape projects and general‑purpose outdoor steel structures.
- Gr.A: Specifies a minimum copper (Cu) content of 0.25 %, providing balanced atmospheric‑corrosion resistance in clean inland atmospheric environments.
- Gr.B: Allows higher maximum limits for chromium (Cr) and nickel (Ni), with improved performance in industrially‑polluted atmospheres.
What is ASTM A709 Gr.50W Weathering Steel Plate?
Core Standard Definition
ASTM A709/A709M‑21 Grade 50W: Structural‑steel specification for bridge use. The suffix "W" stands for weathering grade and is governed by US Department of Transportation (DOT) and AASHTO bridge specifications.
- A709 Gr.50W Type A = chemically and mechanically equivalent to A588 Gr.A
- A709 Gr.50W Type B = chemically and mechanically equivalent to A588 Gr.B
Weathering Mechanism
Alloying elements such as copper, chromium and nickel react under cyclic wet‑dry outdoor atmospheric conditions to form a dense, well‑adherent patina that retards further corrosion of the base metal.
Under typical non‑coastal inland atmospheric conditions, the unpainted service life ranges from 15 to 25 years, roughly 4‑8 times that of conventional carbon‑steel plates.
Important Limitations: Neither grade is fit for permanent submersion in seawater or high‑salinity coastal splash zones. Additional protective coating systems shall be specified for service within these environments.
ASTM A588 Gr.A/B A709 Gr.50W Corten Steel Plate Specification
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Product name |
Corten Steel Plate / Weather Resistant Steel Plate |
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Standard and grade |
ASTM A588 Gr.A / Gr.B; ASTM A709 Gr.50W | |||
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Surface treatment |
Natural oxidation, accelerated oxidation, cleaning and sealing |
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Technique |
Hot treatment,hot rolled or cold rolled,Accelerated oxidation treatment |
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Thickness |
1.5mm-70mm |
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Width |
1000mm-2000mm and customizable |
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Length |
2000mm-12000mm |
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Certificates |
ISO9001,CE and Factory quality certificate |
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Process Service |
Bending, Welding, Cutting, Punching |
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ASTM A588 Gr.A/B vs A709 Gr.50W Weather Resistant Steel Plate Chemical Composition
| Element | ASTM A588 GrA/B | ASTM A709 Gr50W |
|---|---|---|
| C | ≤0.19‑0.21 | ≤0.21 |
| Mn | 0.80‑1.35 | 0.80‑1.35 |
| P | ≤0.035 | ≤0.035 |
| S | ≤0.040 | ≤0.035 |
| Cu | 0.25‑0.60 | 0.25‑0.60 |
| Cr | 0.30‑0.35 | 0.30‑0.35 |
| Ni | ≤0.45 | ≤0.45 |
ASTM A588 Gr.A/B vs A709 Gr.50W Weather Resistant Steel Plate Mechanical Property
| Property | ASTM A588 GrA/B | ASTM A709 Gr50W |
|---|---|---|
| Minimum Yield Strength | 345 MPa (50 ksi) | 345 MPa (50 ksi) |
| Minimum Tensile Strength | 485 MPa (70 ksi) | 485 MPa (70 ksi) |
| Elongation (2 in specimen) | ≥21 % | ≥21 % |
Differences in Low-Temperature Impact Toughness Requirements
A588 Grade A/B: As a general-purpose structural steel, this grade features relatively relaxed toughness specifications. Charpy impact tests are typically conducted at -12°C (10°F) or higher temperatures, depending on plate thickness and customer technical agreements. It cannot be directly substituted for bridge main girders serving in frigid regions.
A709 Grade 50W: Specified specifically for bridge construction, this grade mandates rigorous toughness performance. It is generally required to satisfy Charpy V-notch impact energy requirements at -34°C (-30°F) or lower test temperatures, ensuring the structural safety of bridges operating in cold environments.
ASTM A588 Gr.A/B vs A709 Gr.50W Steel Plate Selection Guide
Choose ASTM A588 Grade A / Grade B
- Grade A: Clean suburban inland atmosphere, architectural facade, corten sculpture, planter boxes, boundary walls.
- Grade B: Industrial zones with sulfide dust pollution, outdoor factory support frames, transmission towers.
Choose ASTM A709 Grade 50W
- Highway & railway bridges, pedestrian overpasses, bridge guardrails for North American public infrastructure tender projects.
- Cold‑climate regions, members subjected to cyclic dynamic load, fracture‑critical bearing components.
- Project documents explicitly specify ASTM A709 series standard.
Send over your local atmospheric environment description (coastal /inland/industrial zone, lowest local ambient temperature) and component load type, we can give direct grade suggestion for your reference.
Why Choose GNEE Steel?
With over 18‑year experience in weathering steel export, we have accumulated rich practical experience for global weathering‑steel purchasers.
- Real‑stock inventory for ASTM A588 GrA/B, A709 Gr50W plates and partial structural shapes, ISO certified, support SGS third‑party witness inspection.
- Deep understanding of ASTM, AASHTO bridge‑related specification; we can review your order specification to help you avoid hidden procurement pitfalls.
- Flexible cooperation modes: bulk stock order, custom mill order, cutting & bending one‑stop processing, small‑batch trial sample order support.
- Complete set of export documents to satisfy North‑America, Latin‑America and European customs clearance and project acceptance.
If you have ongoing projects, share your drawing, required specification, target quantity and delivery destination, our technical‑sales team will reply you with targeted quotation and material suggestion promptly.
Send your drawing, required specification, target quantity and delivery destination
FAQ
Can I use ASTM A588 to replace A709 Grade 50W for US state bridge projects?
Generally, no. You cannot directly substitute ASTM A588 for ASTM A709 Grade 50W on US state bridge projects without explicit approval. While chemically and mechanically similar, A709 is the mandatory specification for bridges and requires specific notch toughness testing (Charpy V-Notch) that A588 does not automatically mandate.
Can bare ASTM A588 / A709 Grade 50W be used in coastal salt spray environment?
No, bare (unpainted) ASTM A588 / A709 Grade 50W weathering steel should not be used in severe coastal salt-spray environments. Airborne chloride ions from marine salt prevent the steel from forming the tight, stable, and protective rust patina (patina) it needs. Instead, continuous salt exposure causes the steel to suffer from ongoing corrosion, flaking, and severe pitting.
What steel grade is ASTM A588 Grade A equivalent to?
ASTM A588 Grade A is commonly equivalent to Corten A (commercial name), EN S355J0W / S355J0WP (European standard), JIS SPA-H (Japanese standard), and GB Q355NH (Chinese standard). It is a high-strength, low-alloy structural weathering steel with a minimum yield strength of 50 ksi.
What is the typical yield strength of ASTM A709 Grade 50W steel?
The typical minimum yield strength of ASTM A709 Grade 50W steel is 50 ksi (345 MPa). This strength requirement applies across standard plate thicknesses up to 4 inches, though minimum yield strength can adjust slightly lower depending on specific heavy structural shapes or very thick profiles per ASTM guidelines.
