4340 Alloy Steel (UNS G43400)
The reference nickel–chromium–molybdenum steel: deep hardenability with dependable toughness across strength levels.
- UNS
- G43400
- W.Nr / EN
- ≈ 36CrNiMo4 / 40NiCrMo8-4 class
- Density
- 7.85 g/cm³
- Service range
- Ambient structural service
About 4340 Alloy Steel
4340 is the reference medium-carbon low-alloy steel. Its nickel–chromium–molybdenum chemistry gives deep hardenability, so heavy sections through-harden and can be tempered anywhere from ~930 to ~1930 MPa to trade strength against toughness. Behaviour at every level is exhaustively documented, which keeps it the default for critical shafts and structural parts.
Vacuum-arc-remelted variants serve fatigue-critical duties. DMK Alloys supplies 4340 as bars and forged blanks, air-melt or remelted quality, heat treated and tested to order.
4340 Alloy Steel chemical composition (weight %)
| Element | Limit / range |
|---|---|
| Fe | Balance |
| C | 0.38 – 0.43 |
| Ni | 1.65 – 2.00 |
| Cr | 0.70 – 0.90 |
| Mo | 0.20 – 0.30 |
| Mn | 0.60 – 0.80 |
| Si | 0.15 – 0.35 |
| P | ≤ 0.035 |
| S | ≤ 0.040 |
Composition limits per the commonly referenced standards listed below. Order-specific limits may differ — confirm against the governing specification.
4340 Alloy Steel mechanical properties (typical)
| Condition / form | Tensile, MPa | 0.2% Yield, MPa | Elongation, % |
|---|---|---|---|
| Bar, quenched + tempered (typical aircraft level) | 1240 – 1380 | ≥ 1080 | ≥ 10 |
| Bar, normalized + tempered | ≈ 965 | ≈ 655 | ≈ 17 |
Values are typical or specification-minimum levels for guidance only — not a guarantee of properties. Certified values are established by testing against the ordered specification.
4340 Alloy Steel specifications & international equivalents
| System | Designation | Covers |
|---|---|---|
| UNS | G43400 | All product forms |
| AMS | AMS 6414 | Bars, forgings (VAR) |
| AMS | AMS 6415 | Bars, forgings |
| ASTM | ASTM A322 4340 | Hot-wrought bars |
Cross-references are for guidance; the governing document is always the specification cited on your purchase order or drawing.
4340 Alloy Steel physical properties
| Property | Typical value |
|---|---|
| Density | 7.85 g/cm³ |
| Melting range | ≈ 1425 °C |
| Modulus of elasticity (family-typical) | ≈ 190 – 210 GPa |
| Indicative service range | Ambient structural service |
Forms we manufacture
- Bars
- Forged blanks
- Machined components to drawing
Dimensional ranges and delivery conditions are confirmed per enquiry.
Where 4340 Alloy Steel earns its keep
Typically specified for:
- Power-transmission shafts
- Gears
- Crankshafts
- Landing-gear parts
- Heavy-duty structural members
Also consider
17-4PH Stainless
UNS S17400 · W.Nr 1.4542AMS 5643 · AMS 5604
Martensitic precipitation-hardening stainless steel — high strength and corrosion resistance from a single low-distortion age.
300M Alloy Steel
UNS K44220AMS 6257 · AMS 6417
Ultra-high-strength low-alloy steel — ~1930–2070 MPa with the toughness demanded of landing-gear-class parts.
440C Stainless
UNS S44004 · W.Nr 1.4125AMS 5630 · AMS 5618
The hardest standard stainless steel: bearing-grade wear resistance at up to ~60 HRC with corrosion protection.
Request 4340 Alloy Steel to your specification
State the governing standard, form, dimensions, quantity and testing requirements — the export team responds with a manufacturer's quotation.