8640
Data verified8640 is the 0.40% carbon triple-alloy Q&T steel: 4140-class strength with nickel for extra toughness, common in aircraft-quality bar specifications. It bridges general engineering and aerospace practice.
Chemical composition
| Element | Content (%) |
|---|---|
| C | 0.38–0.43 |
| Si | 0.15–0.35 |
| Mn | 0.75–1.00 |
| P | ≤0.035 |
| S | ≤0.040 |
| Cr | 0.40–0.60 |
| Ni | 0.40–0.70 |
| Mo | 0.15–0.25 |
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 | 950–1200 MPa (Q&T, typ.) |
| Density | 7.85 g/cm³ |
Heat treatment
Normalize 870 °C; quench 855 °C oil; temper 500–650 °C.
Equivalent grades
| Standard | Designation |
|---|---|
| aisi | 8640 |
| jis | SNCM240 (near) |
Compare side by side: 8640 vs 8740 · 8640 vs 8630
Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.
Applications & Processing
Applications: Aircraft parts, gears, shafts, high-strength bolts, ordnance components.
Processing: Machines well; vacuum-melt (8640V) versions serve critical rotating parts.
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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.