40CrNiMoA 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.
40CrNiMoA
Alloy & Engineering Steel
40CrNiMoA is the GB/T 3077 Ni-Cr-Mo steel corresponding to AISI 4340 — China’s high-hardenability grade for large, highly loaded Q&T parts, with the “A” suffix marking the high-quality (low P/S) melt.
Standards: DIN 1.6511 (36CrNiMo4, near) · AISI 4340 · JIS SNCM439 (near) · GB 40CrNiMoA (GB/T 3077)
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 | 40CrNiMoA | 4340 |
|---|---|---|
| C | 0.37–0.44 | 0.38–0.43 |
| Si | 0.17–0.37 | 0.15–0.35 |
| Mn | 0.50–0.80 | 0.60–0.80 |
| P | ≤0.035 | — |
| S | ≤0.035 | — |
| Cr | 0.60–0.90 | 0.70–0.90 |
| Ni | 1.25–1.75 | 1.65–2.00 |
| Mo | 0.15–0.25 | 0.20–0.30 |
Properties compared
| Property | 40CrNiMoA | 4340 |
|---|---|---|
| Tensile strength | ≥980 MPa (GB/T 3077 reference Q&T) | 1100–1400 MPa (Q&T) |
| Yield strength | ≥835 MPa (reference) | — |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
| Hardenability | Very high (large sections) | Very high (large sections) |
| Hardness (Q&T) | — | 33–45 HRC typical |
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: 40CrNiMoA · 4340. Substitution decisions for certified parts stay with the design authority.