4340
Data verified4340 is a Ni-Cr-Mo steel with deep hardenability and high fatigue strength, used where 4140 runs out of section size or toughness: landing gear, large shafts and high-strength fasteners.
Chemical composition
| Element | Content (%) |
|---|---|
| C | 0.38–0.43 |
| Si | 0.15–0.35 |
| Mn | 0.60–0.80 |
| Cr | 0.70–0.90 |
| Ni | 1.65–2.00 |
| Mo | 0.20–0.30 |
Weight percent, per the governing standard ranges. Actual values per heat are on the mill certificate.
Properties
| Hardness (Q&T) | 33–45 HRC typical |
| Tensile strength | 1100–1400 MPa (Q&T) |
| Density | 7.85 g/cm³ |
| Hardenability | Very high (large sections) |
Heat treatment
Quench 845 °C oil; temper 425–650 °C — avoid the 250–350 °C tempered-martensite embrittlement range.
Equivalent grades
| Standard | Designation |
|---|---|
| din | 1.6511 (36CrNiMo4) |
| aisi | 4340 |
| jis | SNCM439 |
| gb | 40CrNiMo |
Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.
Applications & Processing
Applications: Aircraft and heavy-vehicle parts, large shafts, gears, high-strength bolts, downhole tools.
Processing: Machines in annealed condition; weld only with strict preheat/post-weld practice; grind after hardening.
FAQ
- 4140 or 4340 for a large shaft?
- Above roughly 100 mm ruling section or for high fatigue duty, 4340’s nickel gives the through-hardness and toughness that 4140 cannot guarantee.
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Ask for a quotationVisit NasteelSource: SAE J404 / ASTM A29 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.