4340 Round Bar: Material Profile
4340 combines nickel, chromium, and molybdenum to provide deep hardenability and strong performance under impact and cyclic loading.
It is available in hot-rolled, cold-finished, annealed, and heat-treated conditions depending on the specification.
Purchase to the controlling ASTM, SAE, AMS, or customer specification. Section size, supply condition, mechanical properties, surface limits, testing, and heat/lot traceability can change the acceptable material and processing route.
Key Characteristics
- High tensile and fatigue strength
- Excellent toughness
- Deep hardenability
- Good machinability when annealed
Common Applications
- Crankshafts and gears
- Aircraft and defense components
- Power-transmission parts
- Heavy-equipment and oil-and-gas shafts
Typical Chemical Range
| Element | Weight % |
|---|---|
| Carbon | 0.38–0.43 |
| Manganese | 0.60–0.80 |
| Silicon | 0.15–0.35 |
| Nickel | 1.65–2.00 |
| Chromium | 0.70–0.90 |
| Molybdenum | 0.20–0.30 |
| Phosphorus (max) | 0.035 |
| Sulfur (max) | 0.040 |
Chemistry ranges are general reference values. The purchase specification and material certification govern the order.
