Steel 4340
Steel 4340 – Ultra-High-Strength Ni-Cr-Mo Alloy Steel for Aircraft and Heavy Machinery
Steel 4340 is a nickel-chromium-molybdenum ultra-high-strength alloy steel with excellent hardenability in thick sections. Its combination of very high strength, outstanding toughness, and deep hardenability makes it the material of choice for aircraft landing gear, crankshafts, and heavy-duty structural components subject to extreme cyclic and impact loading.
Key Properties
- Tensile Strength: 745 MPa (normalized)
- Yield Strength: 470 MPa
- Elongation: 22%
- Hardness: 217 HB
- Hardenability: Excellent in heavy sections
- Standards: AMS 6415 / ASTM A322
Common Applications
Aircraft landing gear, crankshafts, large structural bolts, heavy-section gears, armor plate, motorsport drivetrain components, and power transmission shafts in demanding service.
Material properties
| Material name | Steel 4340 |
|---|---|
| Type | Carbon & Alloy Steel |
| Standard code | AMS 6415 / ASTM A322 |
| Tensile strength (MPa) | 745 |
| Yield strength (MPa) | 470 |
| Fatigue strength (MPa) | 470 |
| Elongation (%) | 22 |
| Hardness (Brinell) | 217 |
| Density (g/cm³) | 7.85 |
| Electrical resistivity (µΩ·in) | 22 |
| Thermal conductivity (W/m·K) | 44.5 |
| Melting range (°C) | 1427–1460 |
| Weldability | Good |
| Formability | Fair |
| Shear modulus | 80 |
| Industry code | carbon_4340 |