SteelWhat is A709 steel and what is it used for? Structural steel for bridges
A709 steel is structural steel for bridges. In this guide we explain what A709 steel is, its composition, its properties, what it is used for and the sizes we stock.
What is A709 steel?
Family of structural steels for bridge construction (ASTM A709 / A709M), in different grades and strength levels. The conventional grades offer good weldability, ductility, and structural performance; it also covers higher-strength variants and grades with improved atmospheric corrosion resistance. For girders, gusset plates, diaphragms, crossbeams, decks, and supports.
Chemical composition of A709 steel
This is the typical composition of A709 steel (ASTM A709 Gr. 50 / EN S355J2 / DIN 1.0577 / JIS SM490 standard):
| Element | Contents | What for? |
|---|---|---|
| Carbon (C) | 0.27 % max. | Adds strength; limited to preserve weldability |
| Manganese (Mn) | 1.35 % max. | Adds strength and hardenability |
| Silicon (Si) | 0.40 % max. | Deoxidizer |
| Phosphorus (P) | 0.030 % max. | Impurity, kept low |
| Sulfur (S) | 0.030 % max. | Impurity, kept low |
A709 grades and properties
A709 is the specification for structural steel for bridges. It brings together several strength grades (36, 50, 50S, 50W, HPS 50W, HPS 70W) equivalent to other structural steels, but with requirements specific to bridges. It includes "W" (weathering) variants with greater atmospheric corrosion resistance, which form a protective patina and reduce maintenance. The most common grade is 50 (345 MPa).
What is it for? Applications of A709
A709 steel is mainly used in:
- Bridge girders
- Structural crossbeams
- Bridge diaphragms
- Connection plates
- Metal panels
- Structural supports
- Walkways and viaducts
- Welded bridge components
- High-load road structures
Forms and sizes we carry
At NAT MAC we stock A709 steel in these forms and sizes:
| Package size | Sizes |
|---|---|
| Plates | 3/16" – 4" (4.76 – 102 mm) |
| Flat bars | Made to length |
If you need a particular size, tell us which one and we will gladly source it for you.
A709 equivalents and standards
A709 steel is also identified by these standards: ASTM A709 Gr. 50 / EN S355J2 / DIN 1.0577 / JIS SM490. You can see how to read them in our article on steel standards.
In summary
- A709 is the structural steel for bridges, with several grades and weathering variants
- The "W" variants resist atmospheric corrosion and reduce maintenance
- For beams, diaphragms, connection plates, decking and bridge supports
- We carry it in plates, flat bars, cut to size
Why buy your A709 steel at NAT MAC?
We have more than 54 years of experience as an industrial supplier and ISO 9001 certified quality. We carry quality structural plate and help you choose the right grade for your project.
- Quality A709 steel plate, with backing and traceability
- Material cut to the size you need
- Technical advice on choosing the right structural steel
- Wide range of structural plate in stock
- On-time deliveries and competitive prices
Tell us what you will make and in what sizes, and we'll recommend the right grade and form. Request your free quote.
Sources: data sheet from our NAT MAC catalog (composition, sizes and applications) and the corresponding ASTM standards. Values are for reference and may vary by grade, standard and heat.
