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Alloy Steel 4340 is a heat-treatable, low-alloy steel containing nickel, chromium and molybdenum. It is known for combining very high strength with excellent toughness. Through our UK CNC machining service, Alloy Steel 4340 CNC parts can be produced as one-off prototypes or repeat batches.
After heat treatment it retains good wear resistance and fatigue strength, making it a strong candidate for highly stressed parts in aerospace, automotive and power transmission. Typical uses include power transmission gears, drive shafts and aircraft landing gear. Its quoted tensile strength of around 820 MPa gives a useful guide when sizing parts.
Components are CNC milled or turned to drawing. A protective finish such as black oxide, plating or oil is recommended for long-term corrosion protection. Upload your CAD file for a quick quote on CNC machining Alloy Steel 4340, with delivery anywhere in the UK.
Material
Alloy Steel 4340
Description
Strengths
Lead time 10 business days. Ni-Cr-Mo steel that heat treats to very high strength while staying tough and fatigue resistant.
Weaknesses
Needs care when welding
Silver grey
Ultimate tensile strength
820 MPa
Yield strength
525 MPa
Modulus of elasticity
213 GPa
Elongation at break
22%
Density
7.85 g/cm³
Hardness
24–53 HRC
Shear modulus
80 GPa
Corrosion resistance
Good (atmospheric)
UK equivalent
EN24 (817M40)
Maximum service temperature
Melting point 1427°C
Thermal expansion coefficient
11.5–13 × 10⁻⁶ /°C
Thermal conductivity
Not specified
Electrical resistivity
Not specified
Heat treatment
Hardening & tempering
Recommended finish
Black oxide, plating or oil
Power transmission gears
Drive shafts
Aircraft landing gear
Heavy-duty structural parts
Values shown are typical supplier figures for Alloy Steel 4340 and may vary with stock condition. Please confirm critical properties before production.
4340 (EN24) machines well in the annealed or hardened-and-tempered condition, but its high strength means slower cutting than mild steel.
4340 suits precise gears and shafts; if parts are heat treated after machining, flag critical features for review. Achievable tolerances depend on part size, geometry and features, so mark any critical tolerances on a 2D drawing with your upload and they will be reviewed and confirmed in your quote.
Yes. 4340 is a nickel-chromium-molybdenum steel that heat treats to very high strength while staying tough and fatigue resistant. Black oxide, plating or oil is recommended for protection, and welding needs care.
Typical uses include power transmission gears, drive shafts, aircraft landing gear and heavy-duty structural parts.
Choose 4340 when the part must combine very high strength with toughness in thicker sections. 4140 is usually enough for general high-strength shafts, bolts and gears.
The typical lead time shown for 4340 steel is 10 business days from an approved order. Heat treatment can add time. Quantity, finishing and any heat treatment can affect this, and your quote confirms the date before you order.
Parts in as fast as 10 business days
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