Material · Carbon, Alloy & Tool Steels
Alloy Steel 4340
The landing-gear steel: maximum strength with toughness for safety-critical rotating parts.
Price index: $$$
Material properties
| Parameter | Value |
|---|---|
| Tensile strength | ~1280 MPa (Q&T) |
| Yield strength | ~1180 MPa (Q&T) |
| Hardness | ~40 HRC (Q&T typical) |
| Density | 7.85 g/cm³ |
Choose it when
The step above 4140 for safety-critical parts: nickel addition preserves toughness at very high strength, so it survives the shock and fatigue that crack lesser steels — the classic landing-gear recipe.
Look elsewhere when
If 4140 pre-hard meets the load case, 4340 just adds cost and harder machining. It is equally rust-prone bare, and welding is even less forgiving than 4140.
Compatible finishes
As-Machined
The baseline finish: straight off the machine, fastest and cheapest.
Black Oxide
Black with zero dimensional change: the gauge-and-tool finish for precision steel.
Zinc Plating
The economy rust-stopper: sacrificial zinc keeps protecting even when scratched.
Nickel Plating (Electrolytic)
Bright, polishable nickel for decorative protection and contact underlayers.
Electroless Nickel Plating (ENP)
Plating without electricity: dead-uniform thickness everywhere, bores and threads included.
Hard Chrome Plating
The hardest plated surface in the shop: ~65 HRC chrome for sliding and abrasive service.
Powder Coating
Baked-on polymer armor: any RAL color, outdoor-proof, the toughest cosmetic coating.
Wet Painting
Any color, any gloss, any substrate: the flexible coat for plastics and appearance prototypes.
PTFE Coating (Teflon)
The slippery armor: fluoropolymer for low friction, non-stick release and chemical inertness.
Laser Marking
Permanent identification with zero dimensional change: serials, logos and codes burned in, not stuck on.
Typical applications
- Landing-gear and high-toughness shafts
- Power transmission gears and couplings
- Crankshafts and heavy axles
- Defense and motorsport drivetrain parts
Compared with similar grades
| Property | Alloy Steel 4340 | Low-Carbon Steel 1018 | Carbon Steel 1045 | Structural Steel A36 |
|---|---|---|---|---|
| Tensile strength | ~1280 MPa (Q&T) | 440 MPa (cold drawn) | 625 MPa (cold drawn) | 400–550 MPa |
| Yield strength | ~1180 MPa (Q&T) | 370 MPa (cold drawn) | 530 MPa (cold drawn) | 250 MPa (min) |
| Hardness | ~40 HRC (Q&T typical) | 126 HB | 179–229 HB | ~120 HB |
| Density | 7.85 g/cm³ | 7.87 g/cm³ | 7.85 g/cm³ | 7.85 g/cm³ |
| Price index | $$$ | $ | $$ | $ |
| Machinability | 2/5 | 4/5 | 3/5 | 4/5 |
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