Material datasheet · Premium low-alloy steel
AISI 4340 Ni-Cr-Mo Alloy Steel
UNS G43400 · Quenched & tempered to target HRC; vacuum-melt grade for aerospace (AMS 6414)
Premium aerospace alloy steel. Deep hardenability + nickel toughness.
Chemical composition
Nominal % by weight.
| Element | % by wt |
|---|---|
| Fe | Bal. |
| C | 0.38–0.43 |
| Ni | 1.65–2.00 |
| Cr | 0.70–0.90 |
| Mo | 0.20–0.30 |
Applicable specifications
AMS / ASTM / MIL.
- AMS 6414
- AMS 6415 (bar, forgings, tubing)
- AMS 6359
- MIL-S-5000
Austenitize 1525°F, oil quench, temper 800–1100°F for target.
Machining guidance
CNC parameters and tooling.
Coated carbide; rigid setup essential
Best machined annealed (~217 HB) before final heat treat. Post-HT operations should be grinding.
Stock & cost
Forms and Q1 2026 pricing.
- Cadmium plate (LHE for hydrogen embrittlement control)
- Hard chrome
- Nickel plate
- Phosphate
Typical applications
Where 4340 Steel is the right pick.
- Aircraft landing gear
- Helicopter rotor shafts
- Heavy crankshafts
- High-stress aerospace fittings
Alternative materials
Substitute or upgrade options.
- 300M (higher strength)
- 4140 (cheaper)
- 15-5PH (corrosion + strength)
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Machine your part in 4340 Steel.
Production CNC milling and turning. Confirm material, inspection and documentation requirements when requesting a quote.
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Aerospace specs that call out this alloy.