SAE/AISI 8740 Alloy Steel (UNS G87400)
SAE/AISI 8740 is a nickel-chromium-molybdenum low-alloy steel with good hardenability, strength, and toughness properties. It is widely used as high-strength forged fasteners.
| Chemical Composition | ||
|---|---|---|
| Element | Min | Max |
| Iron | 96.595% | 97.72% |
| Carbon | 0.38% | 0.43% |
| Chromium | 0.40% | 0.60% |
| Manganese | 0.75% | 1.0% |
| 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.
Click on the icon to switch between Metric and Imperial units.
| 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
AISI 8740 steel is commonly used in various applications where high strength, toughness, and durability are required. Some typical applications of 8740 steel include:
- Aerospace Components: 8740 steel is 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 of 8740 steel 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, 8740 steel finds use in machinery and equipment components subject to heavy loads, such as gears, shafts, and spindles.
- Oil and Gas Industry: In the oil and gas sector, 8740 steel is 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 of 8740 steel make it suitable for various defense and military applications, including firearm components, aircraft structural parts, and military vehicle components.
- Power Transmission: 8740 steel is utilized in power transmission applications, such as shafts, gears, and couplings, where strength, durability, and resistance to wear and fatigue are crucial.
- General Engineering: It is also employed in general engineering applications where high strength and toughness are required, including construction equipment, industrial machinery, and heavy-duty fasteners.