9840 vs 4340
These two grades are listed as equivalents of each other: their chemistry windows overlap and they serve the same applications. They are not always identical — check the differences below before substituting, especially in certified designs.
9840
Alloy & Engineering Steel
9840 is a Ni-Cr-Mo through-hardening steel popular in Latin American specifications for shafts and high-strength parts — between 4140 and 4340 in alloy cost and hardenability.
Standards: AISI 9840 · GB 40CrNiMo (near)
4340
Alloy & Engineering Steel
4340 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.
Standards: DIN 1.6511 (36CrNiMo4) · AISI 4340 · JIS SNCM439 · GB 40CrNiMo
Chemical composition compared (%)
| Element | 9840 | 4340 |
|---|---|---|
| C | 0.38–0.43 | 0.38–0.43 |
| Si | 0.15–0.35 | 0.15–0.35 |
| Mn | 0.70–0.90 | 0.60–0.80 |
| Cr | 0.70–0.90 | 0.70–0.90 |
| Ni | 0.85–1.15 | 1.65–2.00 |
| Mo | 0.20–0.30 | 0.20–0.30 |
Properties compared
| Property | 9840 | 4340 |
|---|---|---|
| Hardness (Q&T) | 30–42 HRC typical | 33–45 HRC typical |
| Tensile strength | 1000–1250 MPa (Q&T) | 1100–1400 MPa (Q&T) |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
| Hardenability | — | Very high (large sections) |
Sourcing either grade?
Nasteel stocks both families from Shenzhen with EN 10204 3.1 mill certificates by heat number.
Ask for a quotationSee full data sheets: 9840 · 4340. Substitution decisions for certified parts stay with the design authority.