ASTM A709 Grade 50W Steel Plates – Weathering (Corten) Bridge Steel
ASC LLP, Mumbai, supplies ASTM A709 Grade 50W steel plates (A709M Grade 345W) in 6 mm to 100 mm thickness, from approved mills. In addition, every plate comes with an EN 10204 3.1 certificate showing chemistry, tensile and Charpy results. See also our full range of corten steel plates.
What is ASTM A709 Grade 50W?
ASTM A709 is the specification for structural steel for bridges. Within it, Grade 50W is the 345 MPa (50 ksi) weathering steel, often called corten. Its small additions of copper, chromium, nickel and vanadium let it form a tight, protective rust layer (patina), so bridge girders can often be left unpainted.
The chemistry of Grade 50W is the same as ASTM A588 Grades A and B. However, A709 adds bridge-specific Charpy impact testing by temperature zone, which is why highway authorities specify A709 50W rather than A588 for bridge members.
A709 Grade 50W – Quick Facts
- Specification: ASTM A709 / A709M, Grade 50W [345W]
- Strength: 345 MPa (50 ksi) yield min, while tensile is 485 MPa (70 ksi) min
- Chemistry: Type A or Type B, equivalent to A588 Grades A and B
- Thickness: up to 100 mm (4 in) for plates
- Corrosion index: 6.0 min to ASTM G101, as with other weathering grades
- Impact testing: Charpy by bridge temperature zone 1, 2 or 3
How A709 Grade 50W Weathering Steel Works
When bare 50W steel is exposed to normal wet-dry cycles, it first rusts like ordinary steel. However, within a few years the alloying elements make the rust layer dense and adherent, so it slows further corrosion to a very low rate. As a result, the patina turns a stable dark brown, and maintenance painting is usually not needed.
The patina needs the surface to dry out regularly. Therefore, bare weathering steel is not recommended where it stays wet for long periods, in marine or coastal sites with heavy salt spray, under heavy de-icing salt runoff, or in industrial atmospheres with high sulphur levels. In those cases, 50W is painted, or detailing is improved to keep water off the steel.
Advantages of A709 Grade 50W Plates
- Lower life-cycle cost: unpainted girders avoid initial painting and, in addition, repainting during service.
- Bridge-grade toughness: Charpy testing by temperature zone, so the plate suits the bridge location.
- Good weldability: moderate carbon; moreover, weathering-grade consumables give matching colour and corrosion resistance.
- Architectural finish: similarly, the brown patina is used deliberately on façades and landscape structures.
Applications of ASTM A709 Grade 50W Steel Plates
| Application | Typical A709 Grade 50W use |
| Highway bridges | Plate girders, box girders and cross frames, because bare 50W avoids repainting |
| Railway bridges | Girders and bearing stiffeners, while dry-wet cycles allow a patina to form |
| Highway structures | Sign structures, light poles and noise barriers |
| Architecture | Façades, sculptures and landscape walls, especially where the rust colour is wanted |
A709 Grade 50W Plate Sizes
| Thickness (mm) | Typical width × length (mm) |
| 6 – 25 | 1500 – 3000 × up to 12000 |
| 25 – 50 | likewise 1500 – 3000 × up to 12000 |
| 50 – 100 | 2000 – 3000 × as per order |
Grade 50W plates are limited to 100 mm (4 in) thickness. For thicker or higher-strength weathering plates, HPS 50W or HPS 70W is specified instead. In addition, plates can be supplied cut to size or as flame-cut girder flanges and webs.
ASTM A709 Grade 50W Mechanical Properties
| Property | A709 Grade 50W [345W] |
| Yield strength, min | 345 MPa (50 ksi) |
| Tensile strength, min | 485 MPa (70 ksi) |
| Elongation in 200 mm, min | 18% |
| Elongation in 50 mm, min | 21% |
Unlike some grades, 50W has a minimum tensile strength but no maximum. By contrast, plain Grade 50 has a lower tensile minimum of 450 MPa (65 ksi).
A709 Grade 50W Plate Specifications
| Item | Details |
| Specification | ASTM A709 / A709M, Grade 50W [345W]; also dual-certified to A588 on request |
| General requirements | ASTM A6 / A6M, which also covers tolerances |
| Condition | As-rolled, or alternatively as specified by the mill route |
| Impact testing | Charpy V-notch to the bridge zone, for either non-fracture-critical (T) or fracture-critical (F) members |
| Corrosion resistance | Atmospheric corrosion index 6.0 min, calculated to ASTM G101 |
| Certificate | EN 10204 3.1; in addition, 3.2 and third-party inspection on request |
A709 Grade 50W Charpy Impact – Temperature Zones
| Zone | Minimum service temperature | Non-fracture-critical test temperature (up to 50 mm) |
| Zone 1 | 0 °F (−18 °C) | 70 °F (21 °C) |
| Zone 2 | below 0 to −30 °F (−18 to −34 °C) | 40 °F (4 °C) |
| Zone 3 | below −30 to −60 °F (−34 to −51 °C) | 10 °F (−12 °C) |
For non-fracture-critical members up to 50 mm thick, the minimum average is 15 ft·lbf (20 J) at the zone test temperature; thicker plates need more. Fracture-critical members, meanwhile, have higher energy requirements. Therefore, always state the zone and member type (T or F) on the order.
ASTM A709 Grade 50W Chemical Composition
| Element | Type A (%) | Type B (%) |
| Carbon (C), max | 0.19 | 0.20 |
| Manganese (Mn) | 0.80 – 1.25 | 0.75 – 1.35 |
| Phosphorus (P), max | 0.04 | also 0.04 |
| Sulphur (S), max | 0.05 | again 0.05 |
| Silicon (Si) | 0.30 – 0.65 | 0.15 – 0.50 |
| Nickel (Ni), max | 0.40 | 0.50 |
| Chromium (Cr) | 0.40 – 0.65 | 0.40 – 0.70 |
| Copper (Cu) | 0.25 – 0.40 | 0.20 – 0.40 |
| Vanadium (V) | 0.02 – 0.10 | 0.01 – 0.10 |
Type A and Type B are equivalent to A588 Grades A and B. Copper, chromium and nickel together form the protective patina, whereas vanadium adds strength.
A709 Grade 50W vs Grade 50 vs HPS 50W vs A588
| Grade | Yield / tensile, min (MPa) | Weathering? | Typical use |
| A709 Grade 50 | 345 / 450 | No, so it must be painted | Painted bridge members |
| A709 Grade 50W | 345 / 485 | Yes | Unpainted bridge girders |
| A709 HPS 50W | 345 / 485 | Yes, with better toughness and weldability | Fracture-critical members |
| ASTM A588 | 345 / 485 | Yes | General structures, since it has no bridge Charpy zones |
In short, 50W has the same chemistry as A588 but adds bridge impact testing. HPS 50W, on the other hand, is a high-performance version with lower carbon and better toughness. See also ASTM A242, A606 Type 4 and A709 Grade 100 plates.
Welding A709 Grade 50W
- Bare (unpainted) structures: weathering-grade consumables, for example E8018-W1/W2 or matching wire, so the weld develops the same patina.
- Single-pass small welds: standard E70-class consumables are often acceptable, because base-metal dilution gives some weathering resistance.
- Preheat: as required by AWS D1.5 for bridge welding, depending on thickness.
For matching weathering pipe and tube, see our ASTM A847 corten pipes and corten steel tubes.
Why Buy A709 Grade 50W Plates from ASC LLP?
- Traceable material: EN 10204 3.1 certificates with chemistry, tensile and Charpy results.
- Correct ordering: help stating zone, T or F member and thickness, because these set the impact test.
- Cutting: plates cut to size or flame-cut to girder dimensions.
- Export packing: finally, plates are marked and packed for sea shipment.
See also our corten steel range.
Frequently Asked Questions – ASTM A709 Grade 50W Plates
What is ASTM A709 Grade 50W?
In short, A709 Grade 50W is a 345 MPa (50 ksi) weathering structural steel for bridges. It forms a protective patina, so it can often be used unpainted.
What are the mechanical properties of A709 Grade 50W?
It has 345 MPa (50 ksi) minimum yield and 485 MPa (70 ksi) minimum tensile strength. In addition, elongation is 21% in 50 mm and 18% in 200 mm.
What is the chemical composition of ASTM A709 50W?
It is supplied as Type A or Type B, equivalent to A588 Grades A and B. For example, Type A has C 0.19% max, Mn 0.80–1.25%, Cr 0.40–0.65%, Cu 0.25–0.40% and V 0.02–0.10%.
Is A709 Grade 50W the same as corten steel?
Broadly, yes. “Corten” is a common name for weathering steel, and 50W is the bridge-specification weathering grade.
What is the difference between A709 Grade 50 and 50W?
Grade 50 is not weathering steel, so it must be painted. 50W, by contrast, contains Cu, Cr, Ni and V and has a higher tensile minimum of 485 MPa.
What is the maximum thickness of A709 Grade 50W plate?
Plates are covered up to 100 mm (4 in). Above that, or for better toughness, HPS grades are usually specified.
Where should weathering steel not be used bare?
Avoid bare 50W where it stays wet, near the sea with salt spray, under heavy de-icing salt or in high-sulphur industrial air; instead, paint it in those locations.
Global Supply
ASC LLP supplies ASTM A709 Grade 50W steel plates from Mumbai to customers in India, the Middle East, Europe, Africa, the Americas and South-East Asia. To get a prompt quotation, simply send your enquiry with thickness, size, bridge zone and quantity.
Countries We Export To
UNITED STATES, EUROPE, UK, UAE, SAUDI ARABIA, OMAN, KUWAIT, JORDAN, QATAR, INDONESIA, MALAYSIA, BRAZIL, SPAIN, ITALY, FRANCE, GERMANY, BAHRAIN, SRI LANKA, AZERBAIJAN, AUSTRALIA, AUSTRIA, PHILIPPINES, TURKEY, RUSSIA, IRAN, IRAQ, CANADA, KOREA, JAPAN, YEMEN, FINLAND, ZIMBABWE, HUNGARY, PORTUGAL, VIETNAM, MOROCCO, THAILAND, SOUTH AFRICA, MEXICO, SINGAPORE, GREECE, KUWAIT, POLAND, NEW ZEALAND, SWEDEN, SWITZERLAND, BELGIUM, BHUTAN, BANGLADESH, TAIWAN, ROMANIA, CAMBODIA, KAZAKHSTAN, AFGHANISTAN.
