What is A656 Grade 70?
A656 Grade 70 is a high-strength, low-alloy (HSLA) structural steel plate conforming to ASTM A656. The "70" indicates a minimum yield strength of 70 ksi (≈485 MPa). It is designed for heavy structural applications requiring high load-bearing capacity, excellent toughness, and good weldability. Typical applications include bridges, high-rise buildings, heavy machinery frames, storage tanks, and pressure vessels. The steel is usually supplied in a normalized or controlled-rolled condition, which ensures a fine-grained microstructure and consistent mechanical properties.
Typical Chemical Composition (wt%)
| Element | Typical / Max Value |
|---|---|
| Carbon (C) | ≤ 0.23% |
| Manganese (Mn) | 1.35% max |
| Silicon (Si) | 0.40% max |
| Phosphorus (P) | ≤ 0.035% |
| Sulfur (S) | ≤ 0.035% |
| Copper (Cu) | 0.20–0.40% (optional) |
| Nickel (Ni) | 0.25% max (optional) |
| Chromium (Cr) | 0.35% max (optional) |
| Molybdenum (Mo) | 0.10% max (optional) |
Typical Mechanical Properties
| Property | Value |
|---|---|
| Minimum Yield Strength | 485 MPa (70 ksi) |
| Tensile Strength | 535–690 MPa (77–100 ksi) |
| Elongation | ≥ 18% |
| Hardness | Brinell ≤ 235 HB |
What's its commonly application?
A656 Grade 70 steel is primarily used in heavy structural applications due to its high yield strength (485 MPa / 70 ksi), excellent tensile strength, toughness, and weldability. Its common applications include:
Bridges – Girders, beams, and trusses requiring high load-bearing capacity, especially for long spans.
High-Rise and Industrial Buildings – Columns, beams, and structural framing where heavy loads must be supported.
Heavy Machinery – Frames and components of cranes, loaders, and other construction or industrial equipment, providing resistance to impact and dynamic loads.
Pressure Vessels and Storage Tanks – Thick-walled tanks and vessels where both strength and toughness are critical.
Industrial Structures – Platforms, piping racks, supports, and welded assemblies in factories or refineries.
Cold or Moderate Low-Temperature Environments – Areas where low-temperature toughness and ductility are important to prevent brittle fracture.
In general, A656 Grade 70 is chosen wherever high strength, thick plates, and structural reliability are required.
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