What is ASTM A709 grade 50W weathering steel?
ASTM A709 Grade 50W is a high-strength weathering steel designed for unpainted bridge construction, offering a minimum yield strength of 50 ksi (345 MPa) and mandatory impact toughness.** Its key characteristic is the formation of a dense, protective rust patina-due to added alloying elements like copper, chromium, and nickel-that inhibits further atmospheric corrosion, eliminating the need for paint systems and providing significant long-term maintenance savings. This self-protecting, 50 ksi structural steel is the code-specified material for exposed, aesthetically distinctive highway bridges where durability and lifecycle cost efficiency are paramount.
Key Properties of ASTM A709 Grade 50W
| Property | Specification / Characteristic |
|---|---|
| Yield Strength | Minimum 50 ksi (345 MPa) |
| Tensile Strength | Minimum 65 ksi (450 MPa) |
| Key Alloying Elements | Added Copper (Cu), Chromium (Cr), Nickel (Ni), and sometimes Silicon (Si) beyond standard Grade 50. |
| Corrosion Resistance | ~4-6 times the atmospheric corrosion resistance of plain carbon steel (e.g., A36). The patina typically forms within 1-3 years of exposure. |
| Impact Toughness | Mandatory. Must meet Charpy V-notch requirements (e.g., ≥ 20 ft-lb @ 70°F) as per A709. |
| Appearance | Develops a distinctive, uniform russet-brown to dark purple patina. |
A709 Grade 50W Corrosion Resistant Steel Plate Chemical Composition
| Type | Thickness (in) | C (max wt %) |
Mn (wt %) |
P (max wt %) |
S (max wt %) |
Si (wt %) |
V (wt %) |
Cr (wt %) |
Ni (max wt %) |
Cu (wt %) |
|---|---|---|---|---|---|---|---|---|---|---|
| A | 0.1875 - 2.00 | 0.19 | 0.80 - 1.25 | 0.030 | 0.030 | 0.30 - 0.65 | 0.02 - 0.10 | 0.40 - 0.65 | 0.40 | 0.25 - 0.40 |
| B | 2.00 - 3.00 | 0.20 | 0.75 - 1.35 | 0.030 | 0.030 | 0.15 - 0.50 | 0.01 - 0.10 | 0.40 - 0.70 | 0.50 | 0.20 - 0.40 |
A709 Grade 50W Corrosion Resisting Structural Steel Mechanical Properties
| Grade | Thickness (in) |
Yield strength (min ksi) |
Tensile strength (min ksi) |
Elongation in 2" (min %) |
Elongation in 8" (min %) |
|---|---|---|---|---|---|
| 50W | 0.1875 - 3.00 | 50 | 70 | 21 | 18 |
Summary
ASTM A709 Grade 50W is not just a strong steel; it is a sustainable, low-maintenance engineering solution. It combines the structural efficiency of 50 ksi strength with the durability of a protective patina, making it the premier choice for signature, exposed bridges and infrastructure where long-term performance and aesthetics are prioritized over initial paint systems. Its successful use depends entirely on proper design for exposure and an understanding of its weathering process.
What is A709 grade 50W steel?
ASTM A709-50W is a standard specification for structural steel primarily in the fabrication of steel bridges. ASTM A709-50W covers high strength, low allow steel structural shapes, plates and bars.
What is ASTM A709 steel grade?
The ASTM A709 is the Standard Specification for Structural Steel for Bridges and encompasses carbon, high-strength low-alloy, and quenched and tempered alloy steels used as structural plates in the construction of bridges. SSAB offers the following five grades of A709; 36, 50, 50W, HPS 50W and HPS 70W.
What is the difference between ASTM A572 Grade 50 and ASTM A709 Grade 50?
A572 Grade 50: Used in a wide range of structural applications, including buildings, transmission towers, equipment, and general construction. It's not specifically optimized for bridges. A709 Grade 50: Primarily used for bridge construction and other structures where enhanced toughness and weldability are critical.
What is the yield strength of ASTM A709 grade 50?
Grade 50 steel of this specification requires a minimum yield strength of 50 ksi. Used as structural members in bridge building or for similar structures.
What is the difference between ASTM A36 and A709?
ASTM A709 grade 36 is a bridge material wherein carbon adds to the strength and hardenability of the steel. A36 has less than0. 30% carbon and thus, do not possess high hardenability. ASTM A709 grade 36 steel plate has improved corrosion resistance and can be used in outdoor applications.
Full specification and details are available on request. The above information is provided for guidance purposes only. For specific design requirements please contact our technical sales staff.
