SAE/AISI 8720 Alloy Steel (UNS G87200)
SAE/AISI 8720 is a nickel-chromium-molybdenum low-alloy steel designed for case-hardening applications. Offering a combination of good machinability, wear resistance, and toughness, it performs well under high stress and can be heat treated to enhance its mechanical properties.
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| Chemical Composition | ||
|---|---|---|
| Element | Min | Max |
| Iron | 96.89% | 97.97% |
| Carbon | 0.18% | 0.23% |
| Chromium | 0.40% | 0.60% |
| Manganese | 0.70% | 0.90% |
| Molybdenum | 0.20% | 0.30% |
| 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 8720 properties in both SI and US customary/Imperial units.
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| Physical Properties | Metric |
|---|---|
| Density | 7850 kg/m3 |
| Mechanical Properties | Metric |
| Young’s Modulus (E) | 190 - 210 GPa |
| Bulk Modulus (K) | 140 GPa |
| Shear Modulus (G) | 80 GPa |
| Poisson’s Ratio (ν) | 0.27 - 0.30 |
| Brinell Hardness | 179 - 235 |
| Thermal Properties | Metric |
| Thermal Conductivity | 46.6 W/m·K |
| Specific Heat Capacity (Cp) | 470 J/kg·K |
| Coefficient of Thermal Expansion (αL) | 1.1×10-5 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 8720 Alloy Steel
| Advantages | Disadvantages |
|---|---|
| High strength and toughness | Relatively low corrosion resistance |
| Excellent wear resistance | Limited weldability |
| Good hardenability and case depth | Requires careful heat treatment to achieve desired properties |
| Suitable for applications requiring high load-bearing capacity | Susceptible to cracking if not properly heat treated |
| Resistant to fatigue and impact | Higher cost compared to carbon steels |
Applications of 8720 Alloy Steel
Thanks to its high strength, toughness, and wear resistance, AISI 8720 steel is used across several industries in critical components, including:
- Gears and Gear Shafts: Excellent wear resistance and high load-bearing capacity make it suitable for manufacturing gears and gear shafts used in heavy machinery, automotive transmissions, and power transmission systems.
- Bolts and Fasteners: Due to its high strength and toughness, it is often used to produce bolts, screws, and other fasteners for applications that require reliability, resistance to fatigue, and the ability to withstand high stress.
- Bearings: The wear resistance and hardness make it suitable for producing bearings, especially in applications where high load capacities, toughness, and resistance to wear are crucial.
- Axles and Shafts: Utilized in the production of axles and shafts for industries such as automotive, agriculture, and construction, offering strength, toughness, and resistance to bending and torsion.
- Hydraulic Components: High strength and fatigue resistance make it suitable for hydraulic components such as pistons, rods, and cylinders.
- Tooling and Dies: Sometimes used in tooling and die manufacturing for applications requiring high strength, wear resistance, and toughness, including forging dies, die casting molds, and extrusion tooling.