ASTM A709/A709M Grade 50S High-Strength Low-Alloy Steel Coil
ASTM A709/A709M Grade 50S High-Strength Low-Alloy Steel Coil for Bridges
Comprehensive material data for ASTM A709/A709M Grade 50S carbon and low-alloy high-strength structural steel coil, including chemical composition, mechanical properties, physical properties, international equivalents and application guidance for bridge construction.
Hot rolling; welding; bolting; cutting; machining; forming; cold bending; thermal cutting
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ASTM A709/A709M Grade 50S High-Strength Low-Alloy Steel Coil Introduction
ASTM A709/A709M Grade 50S (also designated Grade 345S in metric) is a carbon and low-alloy high-strength structural steel primarily supplied in coil, plate, bars and structural shapes for use in highway bridge construction. It meets the strength and toughness requirements of the ASTM A709/A709M specification. Grade 50S provides a minimum yield strength of 50 ksi (345 MPa) and minimum tensile strength of 65 ksi (450 MPa). The steel offers good weldability, formability and notch toughness when specified. It is typically produced by hot rolling and may be delivered in as-rolled, normalized or thermo-mechanical control processed (TMCP) condition. Typical applications include main girders, cross frames, splice plates, stiffeners and other primary load-bearing bridge members. When more stringent impact energy requirements are needed, supplementary specifications for Charpy V-notch testing can be applied.
ASTM A709/A709M Grade 50S High-Strength Low-Alloy Steel Coil Chemical Composition
Chemical composition limits for Grade 50S (Grade 345S) according to ASTM A709/A709M. The values represent the maximum permitted contents unless a range is shown. These requirements ensure adequate strength and weldability for bridge structural applications.
| Element | Standard Value (max, %) | Remarks |
|---|---|---|
| Carbon (C) | 0.23 | Heat analysis |
| Manganese (Mn) | 1.35 a | Heat analysis; for plates and bars ≤ 3/4 in. [19 mm] in thickness |
| Phosphorus (P) | 0.030 | Heat analysis |
| Sulfur (S) | 0.030 | Heat analysis |
| Silicon (Si) | 0.40 | Heat analysis |
| Iron (Fe) | Balance | No specified limits for other elements; residual elements may be present |
ASTM A709/A709M Grade 50S High-Strength Low-Alloy Steel Coil Physical Properties
Typical physical properties for ASTM A709 Grade 50S steel at room temperature, unless otherwise noted. These values are representative of carbon and low-alloy structural steels and may vary with actual composition and heat treatment condition. They are provided for engineering reference and are not part of the specification requirements.
| Property | Typical Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Elastic modulus (E) | 200 | GPa | At room temperature |
| Shear modulus (G) | 77 | GPa | At room temperature |
| Poisson's ratio (ν) | 0.30 | - | At room temperature |
| Thermal expansion coefficient (α) | 11.7 | 10⁻⁶/°C | Between 20 °C and 100 °C |
| Thermal conductivity (λ) | 45 | W/(m·K) | At 20 °C |
| Specific heat capacity | 500 | J/(kg·K) | At 20 °C |
| Electrical resistivity (ρₑ) | 0.15 | μΩ·m | At 20 °C |
ASTM A709/A709M Grade 50S High-Strength Low-Alloy Steel Coil Mechanical Properties
Tensile and bending properties for ASTM A709/A709M Grade 50S as per standard requirements. These values apply to plate, bar and structural shape products. Charpy V-notch impact toughness is not mandatory in the base specification but may be required by the purchasing order through supplementary requirements; therefore it is not listed here.
| Property | Standard Requirement | Unit | Test Condition |
|---|---|---|---|
| Yield strength (ReH) | ≥ 345 | MPa [ksi] | For all thicknesses (min 50 ksi); transverse or longitudinal |
| Tensile strength (Rm) | ≥ 450 | MPa [ksi] | For all thicknesses (min 65 ksi) |
| Elongation (A) in 8 in. (200 mm) | ≥ 18 | % | For plates, bars and structural shapes; based on 8 in. [200 mm] gage length |
| Elongation (A) in 2 in. (50 mm) | ≥ 21 | % | For plates, bars and structural shapes; based on 2 in. [50 mm] gage length |
| Bend test (180°) | No cracks on the outside of the bent portion | - | Bend radius = 2 × specimen thickness for material ≤ 3/4 in. [19 mm] |
ASTM A709/A709M Grade 50S High-Strength Low-Alloy Steel Coil Directly Equivalent Material Standards and Substitutable Grades
| Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA | ASTM A572/A572M | Grade 50 [345] | Identical base chemistry and mechanical properties; A709 Grade 50S is essentially A572 Grade 50 with additional bridge-related test requirements. |
| USA | AASHTO M270/M270M | Grade 50S (Grade 345S) | Identical specification adopted by AASHTO for bridges; fully interchangeable with ASTM A709 Grade 50S. |
| USA | ASME SA709/SA709M | Grade 50S | ASME boiler and pressure vessel code adoption of ASTM A709; identical requirements. |
ASTM A709/A709M Grade 50S High-Strength Low-Alloy Steel Coil Application Introduction
ASTM A709 Grade 50S is engineered specifically for bridge construction but is also suitable for other heavy structural applications. It offers a favorable combination of strength, formability and weldability, making it a versatile choice for load-bearing components that require reliable notch toughness when tested to designated temperatures. Typical uses span highway, railway and pedestrian bridges, as well as industrial frames and offshore platforms.
Product Applications: Bridge girders, trusses and floor beams, Stringers, diaphragms and lateral bracing, Splice plates and gusset plates, Stiffeners and cover plates, Built-up columns and crane runway beams, Sheet pile and king pile for retaining walls, Wind turbine tower sections (when certified for structural use)
Processed into products: Main longitudinal bridge girder webs and flanges, Cross-frame and diaphragm connection plates, Bolted and welded splice connectors, Bearing stiffeners and intermediate stiffeners, Anchor bolt assemblies, Bolted truss chords and web members, Transition plates and expansion joint supports
Application industries: Highway and railway bridge construction, Heavy civil infrastructure, Building and skyscraper structural frames, Offshore and marine structures (platforms, piers), Transmission towers and poles, Mining and heavy machinery support structures
ASTM A709/A709M Grade 50S High-Strength Low-Alloy Steel Coil Similar / Substitute Materials with Comparable Performance
| Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10025-2 | S355JR, S355J0, S355J2 | Nominal yield strength 355 MPa; similar weldability and tensile properties. Impact toughness and some chemistry limits differ; verify equivalence for the specific application. |
| Japan | JIS G3106 | SM490A, SM490B, SM490C | Yield strength 325–365 MPa depending on thickness; widely used for welded structures. Similar strength grade. |
| China | GB/T 1591 | Q345B (now Q355B under GB/T 1591-2018) | 345–355 MPa yield strength; common structural steel. Slight differences in chemical composition and impact requirements. |
| India | IS 2062 | E350 BR / E350 C | 350 MPa minimum yield strength; used for general structural and bridge applications. |
| Russia | GOST 19281 | C345 (S345) | Similar strength level; used in building structures and bridges. |
Notes:
- Notch toughness: When required, Charpy V-notch impact testing must be specified per ASTM A709 supplementary requirements (e.g., temperature zones and min absorbed energy). Grade 50S can be supplied with test temperatures such as 0 °C, -18 °C, -34 °C, etc.
- Weldability: Generally excellent with low carbon equivalent (CE) when controlled chemistry is used. Pre-heating and interpass temperature control may be required for thick sections.
- Corrosion resistance: Grade 50S is not an atmospheric corrosion-resistant (weathering) grade. For unpainted weathering applications, consider ASTM A709 Grade 50W.
- Available forms: Typically delivered as hot-rolled coil, then cut-to-length plate, bars, and structural shapes. Plates up to several inches thick are available.
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