Alloy Steel 4340

Alloy Steel 4340 is a nickel-chromium-molybdenum alloy steel known for its exceptional toughness and high fatigue strength. It is the premium choice for aerospace and defense applications requiring maximum strength and reliability.

Machinability

57/100

Tolerance

±0.01 mm

Category

Carbon & Alloy Steel

Material Properties

PropertyValue
Tensile Strength745 MPa (108 ksi)
Yield Strength470 MPa (68 ksi)
Hardness217 HB
Density7.85 g/cm³
Machinability Rating57/100
Thermal Conductivity44.5 W/m·K
Melting Point1,427–1,477 °C
Tolerance±0.01 mm

Common Grades

4340 Annealed4340 Normalized4340 Q&T

Advantages

  • Exceptional toughness
  • Very high fatigue strength
  • Deep hardenability
  • Excellent impact resistance

Limitations

  • Difficult to machine when hardened
  • Poor corrosion resistance
  • Expensive

Common Applications

Landing gear

Power transmission gears

Crankshafts

Heavy-duty shafts

Structural fasteners

Industries Served

AerospaceDefenseOil & GasAutomotive

Available Surface Finishes

Black OxideHard ChromeCadmium PlatingNitride

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