ASTM A709 Grade 50W (A709GR50W) High-Strength Weathering Steel Plate
ASTM A709 Grade 50W (A709GR50W) High-Strength Weathering Steel Plate: Properties, Equivalents & Applications
Detailed material properties and specifications for ASTM A709 Grade 50W carbon and low-alloy high-strength steel plate, including chemical composition, mechanical properties, physical properties, and international equivalents for structural bridge and outdoor construction applications.
As-rolled, normalized, TMCP, welding, bolting
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ASTM A709 Grade 50W High-Strength Weathering Steel Plate Introduction
ASTM A709 Grade 50W is a high-strength low-alloy structural steel with enhanced atmospheric corrosion resistance (weathering steel). It is primarily specified for bridge construction per ASTM A709/A709M, where the "W" denotes improved resistance to atmospheric corrosion compared to standard carbon steels. This grade provides minimum yield strengths of 50 ksi (345 MPa) for thicknesses up to 4 in. (100 mm) and maintains good weldability and toughness. Its chemical composition meets the requirements of ASTM A588 Grade A or B, ensuring the formation of a protective patina when exposed to outdoor environments, often eliminating the need for painting in many applications. Typical delivery conditions include as-rolled, normalized, or thermo-mechanically controlled processed (TMCP) states, and the material is available in plates, structural shapes, and bars.
- Excellent atmospheric corrosion resistance (weathering grade)
- High strength suitable for weight-critical bridge structures
- Fracture-critical and non-fracture-critical Charpy toughness options
- Weldable by common methods
ASTM A709 Grade 50W High-Strength Weathering Steel Plate Chemical Composition
The chemical composition of ASTM A709 Grade 50W complies with ASTM A588 Grade B (commonly used for plates). Wind elements are controlled to achieve the required weathering properties. Limits are heat analysis values per the standard.
- Copper, chromium, and silicon are essential for atmospheric corrosion resistance.
- Maximum limits ensure weldability and toughness.
| Chemical Element | Standard Value (wt%) | Remarks |
|---|---|---|
| C | 0.20 max | ASTM A588 Grade B |
| Mn | 0.75 – 1.35 | Varies by product thickness |
| P | 0.04 max | |
| S | 0.05 max | |
| Si | 0.15 – 0.50 | 0.15–0.40 for plates ≤1.5 in. (40 mm) |
| Ni | 0.50 max | |
| Cr | 0.40 – 0.70 | |
| Cu | 0.20 – 0.40 | Minimum 0.20 for weathering characteristic |
| V | 0.01 – 0.10 |
ASTM A709 Grade 50W High-Strength Weathering Steel Plate Thermal and Electrical Physical Properties
Physical property data for ASTM A709 Grade 50W are typical for low‑alloy steel and are not mandated by the standard. Values are provided for engineering calculations.
- Properties may vary slightly depending on specific heat treatment and composition.
- Thermal expansion and conductivity values are within typical structural steel ranges.
| Property | Standard Requirement Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | ≈ 7850 | kg/m³ | At room temperature |
| Elastic modulus (E) | ≈ 200 (29,000) | GPa (ksi) | Ambient temperature |
| Shear modulus (G) | ≈ 77 (11,200) | GPa (ksi) | Ambient temperature |
| Poisson's ratio (ν) | ≈ 0.29 | – | Ambient temperature |
| Coefficient of thermal expansion (α) | ≈ 11.7 (6.5) | 10⁻⁶/°C (10⁻⁶/°F) | 0–100°C (32–212°F) |
| Thermal conductivity (λ) | ≈ 42 (24) | W/(m·K) (Btu/(h·ft·°F)) | At 20°C |
| Specific heat capacity (c) | ≈ 420 (0.10) | J/(kg·°C) (Btu/(lb·°F)) | Approximate |
| Electrical resistivity (ρₑ) | ≈ 0.17 | μΩ·m | At 20°C |
ASTM A709 Grade 50W High-Strength Weathering Steel Plate Mechanical Properties
Mechanical property requirements for ASTM A709 Grade 50W depend on plate thickness. The standard specifies minimum yield and tensile strengths, minimum elongation in 200 mm (8 in.) and 50 mm (2 in.) gauge lengths, and Charpy V-notch impact values for fracture-critical or non-fracture-critical applications at specified temperature zones.
- Yield and tensile strengths reduce for thicknesses exceeding 4 in. (100 mm).
- Charpy values below are typical for non-fracture-critical (20 J) and fracture-critical (34 J) applications.
| Property | Standard Requirement Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 345 (50) | MPa (ksi) | Thickness ≤ 100 mm (4 in.) |
| Yield Strength (ReH) | ≥ 315 (46) | MPa (ksi) | Thickness > 100–125 mm (>4–5 in.) |
| Yield Strength (ReH) | ≥ 290 (42) | MPa (ksi) | Thickness > 125–200 mm (>5–8 in.) |
| Tensile Strength (Rm) | ≥ 485 (70) | MPa (ksi) | Thickness ≤ 100 mm (4 in.) |
| Tensile Strength (Rm) | ≥ 460 (67) | MPa (ksi) | Thickness > 100–125 mm (>4–5 in.) |
| Tensile Strength (Rm) | ≥ 435 (63) | MPa (ksi) | Thickness > 125–200 mm (>5–8 in.) |
| Elongation (A) | ≥ 18 | % | Gauge length 200 mm (8 in.), thickness ≤ 40 mm (1.5 in.) |
| Elongation (A) | ≥ 21 | % | Gauge length 50 mm (2 in.), thickness ≤ 40 mm (1.5 in.) |
| Elongation (A) | ≥ 16 | % | Gauge length 200 mm, thickness 40–75 mm (1.5–3 in.) |
| Elongation (A) | ≥ 18 | % | Gauge length 50 mm, thickness 40–75 mm |
| Elongation (A) | ≥ 15 | % | Gauge length 200 mm, thickness 75–125 mm (3–5 in.) |
| Elongation (A) | ≥ 17 | % | Gauge length 50 mm, thickness 75–125 mm |
| Charpy V-notch (KV) – non-fracture critical | ≥ 20 (15) | J (ft·lbf) | At specified temperature (e.g., -18°C (0°F) Zone 1) |
| Charpy V-notch (KV) – non-fracture critical | ≥ 20 (15) | J (ft·lbf) | At -1°C (30°F) Zone 2 |
| Charpy V-notch (KV) – non-fracture critical | ≥ 20 (15) | J (ft·lbf) | At 21°C (70°F) Zone 3 |
| Charpy V-notch (KV) – fracture critical | ≥ 34 (25) | J (ft·lbf) | At specified temperature |
ASTM A709 Grade 50W High-Strength Weathering Steel Plate Complete Equivalent Material Standards and Substitutable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA | ASTM A709/A709M | Grade 50W | Primary designation; weathering bridge steel |
| USA | ASTM A588/A588M | Grade A | Weathering steel with lower carbon and manganese; often interchangeable for thickness up to 4 in. |
| USA | ASTM A588/A588M | Grade B | Weathering steel with similar chemistry; commonly used for plates |
| Europe | EN 10025-5 | S355J2W (1.8965) | Weathering structural steel; Charpy at -20°C; similar strength level |
| Europe | EN 10025-5 | S355K2W (1.8967) | Toughness at -20°C; may replace for demanding fracture critical applications |
| Japan | JIS G 3114 | SMA490BW | Weathering steel for welded structures; yield ≥365 MPa for thin plates, but overall equivalent to 345 MPa class |
| China | GB/T 4171 | Q355NH | Weathering structural steel; yield 355 MPa (≥345); impact at 0°C or lower |
ASTM A709 Grade 50W High-Strength Weathering Steel Plate Application Introduction
ASTM A709 Grade 50W is engineered for structural components exposed to atmospheric conditions where enhanced corrosion resistance can reduce life‑cycle costs. Its high strength‑to‑weight ratio makes it ideal for bridges and large infrastructure projects. The material can be processed by welding, bolting, and cutting using standard practices for low‑alloy steels.
Product Applications: Bridge girders, box girders, and truss members, Orthotropic deck plates and stiffeners, Highway sign supports and lighting poles, Architectural facades and exposed structural frames, Transmission and telecommunication towers, Heavy‑duty welded pressure‑retaining plates (non‑ASME)
Processed into products: Main longitudinal bridge girders (I‑beams or box sections), Cross‑frames and diaphragms, Bearing plates and sole plates, Bolted and welded splice plates, Transverse floor beams, Cantilever brackets and sign structures, Base plates for columns and masts
Application industries: Bridge construction and highway infrastructure, Building and civil engineering (exposed structural steel), Energy (transmission towers, wind turbine towers), Marine and port structures (above splash zone), Railway rolling stock and infrastructure
ASTM A709 Grade 50W High-Strength Weathering Steel Plate Similar/Closely Related Substitute Materials
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA | ASTM A572/A572M | Grade 50 | Same minimum yield strength but not weathering; requires protective coating in atmospheric exposure |
| USA | ASTM A242/A242M | Type 2 | Weathering steel with lower strength (yield 42–50 ksi depending on thickness); used in lighter structures |
| Europe | EN 10025-2 | S355J2 | Non-weathering structural steel; equivalent strength but lacks corrosion resistance of 50W |
| International | ISO 4952 | Fe 510B | Weathering steel with yield 355 MPa (formerly Fe510); used in structural applications |
| India | IS 11587 | IRSM 44-97 | Indian structural weathering steel grade; comparable strength and weather resistance |
Notes:
Weathering patina: When exposed to alternating wet/dry cycles, Grade 50W develops a tightly adherent oxide layer that reduces further corrosion. In highly aggressive environments (marine, industrial with high SO₂), periodic washing or a protective coating may be recommended. Welding: Use low‑hydrogen practices and consumables matching the base metal strength; preheating may be needed for thick sections. Availability: Standard thickness ranges up to 8 in. (200 mm) with z‑direction properties available on inquiry.
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