What is A709 Grade HPS70W?
A709 Grade HPS70W is a high-performance weathering steel designed for modern bridge structures. It offers balanced strength, exceptional toughness, and excellent weldability, enabling efficient fabrication and long service life. Its enhanced atmospheric corrosion resistance reduces maintenance demands, especially in harsh environments.
Chemical Composition (Typical / Specification Limits)
| Element | Content (wt.%) |
|---|---|
| Carbon (C) | ≤ 0.11 |
| Silicon (Si) | 0.30 – 0.50 |
| Manganese (Mn) | 1.10 – 1.35 (may be higher for thicker plates) |
| Phosphorus (P) | ≤ 0.020 |
| Sulfur (S) | ≤ 0.006 |
| Chromium (Cr) | 0.45 – 0.70 |
| Copper (Cu) | 0.25 – 0.40 |
| Nickel (Ni) | ≤ ~0.40 |
| Molybdenum (Mo) | 0.02 – 0.08 |
| Vanadium (V) | 0.04 – 0.08 |
| Aluminum (Al, total) | 0.010 – 0.040 |
| Nitrogen (N) | ≤ ~0.015 |
2. Mechanical Properties
| Property | Requirement / Typical Value |
|---|---|
| Yield Strength | ≥ 485 MPa (70 ksi) |
| Tensile Strength | 585 – 760 MPa (85 – 110 ksi) |
| Elongation (2 in / 50 mm) | ≥ 19% |
| Charpy V-Notch Toughness | 25–35 ft-lb (34–48 J) at –10 °F (–23 °C), depending on application |
What are the differences between them?
A709 Grade 100 and A709 Grade HPS70W are both high-strength structural steels used in bridge construction.
Grade 100 offers higher strength, while HPS70W provides high performance, improved toughness, better weldability, and weathering resistance.
Chemical Composition Comparison (Typical Values)
| Element (wt.%) | A709 Grade 100 | A709 Grade HPS70W |
|---|---|---|
| Carbon (C) | ≤ 0.20 | ≤ 0.11 |
| Manganese (Mn) | 0.80 – 1.70 | 1.10 – 1.35 |
| Phosphorus (P) | ≤ 0.035 | ≤ 0.020 |
| Sulfur (S) | ≤ 0.040 | ≤ 0.006 |
| Silicon (Si) | 0.15 – 0.40 | 0.30 – 0.50 |
| Nickel (Ni) | - | ≤ 0.40 |
| Chromium (Cr) | - | 0.45 – 0.70 |
| Copper (Cu) | - | 0.25 – 0.40 |
| Molybdenum (Mo) | - | 0.02 – 0.08 |
| Vanadium (V) | ≤ 0.08 | 0.04 – 0.08 |
| Aluminum (Al) | ≤ 0.040 | 0.010 – 0.040 |
Key difference:
HPS70W uses a low-carbon, micro-alloyed, weathering-steel chemistry, improving weldability and atmospheric corrosion resistance.
2. Mechanical Properties Comparison
| Property | A709 Grade 100 | A709 Grade HPS70W |
|---|---|---|
| Yield Strength | ≥ 690 MPa (100 ksi) | ≥ 485 MPa (70 ksi) |
| Tensile Strength | 760 – 895 MPa (110 – 130 ksi) | 585 – 760 MPa (85 – 110 ksi) |
| Elongation | ~18% | ≥ 19% |
| Charpy V-Notch Toughness | Typically moderate | High toughness, ≥ 25–35 ft-lb at –10°F |
| Weldability | Moderate (higher preheat often needed) | Excellent (low carbon) |
| Weathering Resistance | Optional / limited | Built-in atmospheric corrosion resistance |
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