SAE/AISI 8740 Alloy Steel (UNS G87400)
SAE/AISI 8740 is a low-alloy steel primarily composed of nickel, chromium, and molybdenum. Renowned for its excellent hardenability, strength, and toughness, it is commonly used in demanding structural and mechanical applications, particularly those requiring high fatigue resistance and durability under stress.
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| Chemical Composition | ||
|---|---|---|
| Element | Min | Max |
| Iron | 96.59% | 97.72% |
| Carbon | 0.38% | 0.43% |
| Chromium | 0.40% | 0.60% |
| Manganese | 0.75% | 1.00% |
| 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 8740 properties in both SI and US customary/Imperial units.
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| Physical Properties | Metric |
|---|---|
| Density | 7850 kg/m3 |
| Mechanical Properties | Metric |
| Tensile Strength (Ultimate) | 695 MPa |
| Tensile Strength (Yield) | 415 MPa |
| Young’s Modulus (E) | 190 - 210 GPa |
| Bulk Modulus (K) | 140 GPa |
| Shear Modulus (G) | 80 GPa |
| Elongation at Break | 22% |
| Poisson’s Ratio (ν) | 0.27 - 0.30 |
| Brinell Hardness | 201 |
| Izod Impact | 41 J |
| 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 8740 Alloy Steel
| Advantages | Disadvantages |
|---|---|
| High strength and toughness | Moderate weldability |
| Excellent hardenability and heat treatability | Susceptible to corrosion |
| Good fatigue resistance | Limited availability in certain regions |
| Wear resistance | Relatively high cost compared to standard steels |
Applications of 8740 Alloy Steel
SAE/AISI 8740 alloy steel is widely utilized across industries that demand strength, toughness, and reliability under stress, including:
- Aerospace Components: Utilized in the manufacturing of aircraft landing gear components, such as landing gear struts, shafts, and axles.
- Automotive Industry: The high strength and wear resistance make it suitable for automotive applications. It can be found in critical components such as crankshafts, connecting rods, and gears.
- Machinery and Equipment: Due to its toughness and fatigue resistance, it finds use in machinery and equipment components subject to heavy loads, such as gears, shafts, and spindles.
- Oil and Gas Industry: Employed in drill collars, tool joints, and other downhole equipment subjected to high mechanical stress and harsh operating conditions.
- Defense and Military Applications: The high strength and toughness properties make it suitable for firearm components, aircraft structural parts, and military vehicle components.
- Power Transmission: Utilized in power transmission applications, such as shafts, gears, and couplings, where strength, durability, and resistance to wear and fatigue are crucial.