9840
Data verified9840 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.
Chemical composition
| Element | Content (%) |
|---|---|
| C | 0.38–0.43 |
| Si | 0.15–0.35 |
| Mn | 0.70–0.90 |
| Cr | 0.70–0.90 |
| Ni | 0.85–1.15 |
| 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) | 30–42 HRC typical |
| Tensile strength | 1000–1250 MPa (Q&T) |
| Density | 7.85 g/cm³ |
Heat treatment
Quench 845 °C oil; temper 500–650 °C to specification.
Equivalent grades
| Standard | Designation |
|---|---|
| aisi | 9840 |
| gb | 40CrNiMo (near) |
Compare side by side: 9840 vs 4340
Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.
Applications & Processing
Applications: Heavy shafts, gears, mining and agricultural machinery, high-strength bolts.
Processing: As 4340 with slightly easier practice; weld with preheat and qualified procedure.
FAQ
- 9840 vs 4340?
- 4340 carries more nickel (1.65–2.00% vs 0.85–1.15%) and hardens deeper; 9840 is the cost-optimized grade common in Mexican and South American specs.
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Ask for a quotationVisit NasteelSource: SAE J404 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.