ASTM A656/A656M Type 8 Grade 70 Introduce
ASTM A656/A656M Type 8 Grade 70 is a low-carbon, high-strength structural steel plates primarily used for structural applications where lighter weight and improved formability is critical. ASTM A656/A656M is available in four grades: 50, 60, 70, and 80 (most popular) and 100. The symbol A denotes that the material is structural steel. The number following it is the yield strength. The yield strength of ASTM A656/A656M Type 8 Grade 70 steel is specified as 50,000 psi (345 MPa) minimum.
Smelting temperature:1377°C - 1871°C
Application:High-strength low-alloy hot-rolled structural steel plate with improved forgeability
ASTM A656/A656M Type 8 Grade 70 Material Chemical Composition
The chemical composition of the ASTM A656/A656M Type 8 Grade 70 steel are as follows:
| Element | Min | Max |
|---|---|---|
| Carbon (C) | - | 0.1800 |
| Manganese (Mn) | - | 1.6500 |
| PhOsphorus (P) | - | 0.0250 |
| Sulfur (S) | - | 0.0300 |
| Silicon (Si) | - | 0.6000 |
| Vanadium (V) | - | 0.1500 |
| Titanium (Ti) | - | 0.1500 |
| Nitrogen (N) | - | 0.0300 |
| Niobium (Nb) | - | 0.1000 |
| (Nb+V+Ti) | 0.0080 | 0.2000 |
| Sulfur (S) | - | 0.0350 |
ASTM A656/A656M Type 8 Grade 70 Material Mechanical Properties
Tests are conducted to verify the mechanical properties, such as the yield strength, tensile strength, and elongation, of the ASTM A656/A656M Type 8 Grade 70 steel, as required by the standard. There are several types of tests that can be used to verify the material's properties, including Charpy V-notch impact testing and mechanical property testing. The Charpy V-notch test is used to evaluate the toughness of the steel; a high toughness translates to a higher resistance to deformation. Mechanical property testing is used to evaluate the material's tensile strength, yield strength, and elongation, as well as its ductility, resistance to shrinking and thermal expansion, and other properties.
The mechanical properties of the ASTM A656/A656M Type 8 Grade 70 steel are as follows:
| YieldRp0.2 | ≤ 925 (MPa) |
| TeileRm | ≤ 585 (MPa) |
| ImpactKV/Ku | 11(J) |
| ElongationA | 24% |
| Reduction in cross section on fractureZ | 12% |
| As-Heat-Treated Condition | Solution and Aging, Annealing, Ausaging, Q+T,etc |
| Brinell hardness (HBW) | 332 |
ASTM A656/A656M Type 8 Grade 70 Material Thermal Properties
The thermal performance parameters of the ASTM A656/A656M Type 8 Grade 70 steel are as follows:
| Temperature (°C) | 12 | 776 | 533 |
| Modulus of elasticity (GPa) | - | 645 | - |
| Mean coefficient of thermal expaion ×10-6/(°C) | - | - | 11 |
| Thermal conductivity (W/m·°C) | - | 13.3 | 13.2 |
| Specific thermal capacity (J/kg·°C) | - | 344 | - |
| Specific electrical resistivity (Ω mm²/m) | 0.24 | - | - |
| Deity (kg/dm³) | - | - | 133 |
| Poisson’s coefficient, ν | - | - | 424 |
ASTM A656/A656M Type 8 Grade 70 Material Machining Technology
Welding of ASTM A656/A656M Type 8 Grade 70 can be done with conventional welding techniques. A preheat of materials prior to welding is generally not required. Post- weld heat treatment should be considered if any part of the fabrications require a low temperature toughness test. Common welding techniques for ASTM A656/A656M Type 8 Grade 70 are arc welding processes such as shielded metal arc welding, gas metal arc welding, and flux-cored arc welding.