SAE/AISI 8640 Alloy Steel (UNS G86400)
SAE/AISI 8640 is a low-alloy steel recognized for its excellent strength, toughness, and hardenability. Composed primarily of iron with additions of nickel, chromium, and molybdenum, it performs reliably under stress and is widely used in demanding mechanical applications.
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| Chemical Composition | ||
|---|---|---|
| Element | Min | Max |
| Iron | 96.6% | 97.8% |
| Carbon | 0.38% | 0.43% |
| Chromium | 0.40% | 0.60% |
| Manganese | 0.75% | 1.00% |
| Molybdenum | 0.15% | 0.25% |
| Nickel | 0.40% | 0.70% |
| Phosphorous | —— | 0.035% |
| Silicon | 0.15% | 0.30% |
| Sulfur | —— | 0.04% |
The following table provides a list of SAE/AISI 8640 properties in both SI and US customary/Imperial units.
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| Physical Properties | Metric |
|---|---|
| Density | 7700 - 8030 kg/m3 |
| Mechanical Properties | Metric |
| Young’s Modulus (E) | 190 - 210 GPa |
| Bulk Modulus (K) | 140 GPa |
| Poisson’s Ratio (ν) | 0.27 - 0.30 |
| Thermal Properties | Metric |
| Thermal Conductivity | 46.6 W/m·K |
| Specific Heat Capacity (Cp) | 470 J/kg·K |
| Coefficient of Thermal Expansion (αL) | 1.3×10-5 1/°C |
| Electrical Properties | Metric |
| Electrical Conductivity | 4.23×106 S/m |
| Electrical Resistivity | 2.36×10-7 Ω·m |
The values in this table are approximate and can vary depending on various factors such as the specific manufacturing process and heat treatment applied to the alloy.
Advantages & Disadvantages of 8640 Alloy Steel
| Advantages | Disadvantages |
|---|---|
| High strength and toughness | Moderate weldability |
| Excellent hardenability | Susceptible to cracking during improper welding |
| Good wear resistance | Relatively high cost compared to carbon steels |
| Enhanced fatigue resistance | Requires careful heat treatment for optimal use |
| Improved impact resistance | Limited availability in certain regions |
Applications of 8640 Alloy Steel
SAE/AISI 8640 steel is utilized across multiple industries due to its strength, toughness, and wear resistance, in applications including:
- Gears and Gear Shafts: Commonly used in the manufacturing of gears, particularly in applications where high strength and wear resistance are required.
- Axles and Shafts: The combination of high strength and toughness makes it suitable for axles and shafts subjected to heavy loads and stresses.
- Fasteners: Utilized in the production of high-strength fasteners such as bolts, studs, and screws.
- Heavy Machinery Components: Due to its excellent hardenability and impact resistance, it is employed in the manufacturing of various heavy machinery components.
- Oil and Gas Industry: Finds application in the oil and gas industry, particularly in drilling equipment and components.
- Automotive Industry: Used in the automotive industry for manufacturing components such as forged parts, transmission gears, and differential components.
- Aerospace Industry: The high strength and toughness make it suitable for certain aerospace applications.