Alloy Steel 4340
Material Data Sheet
AISI 4340 (E4340) alloy steel is a medium carbon, low alloy steel known for providing a good balance between strength and malleability. Alloy 4340 is composed of (descending in order by weight): iron, nickel, chromium, manganese, carbon, molybdenum, silicon, phosphorus and sulfur. With proper working and strengthening, items made from 4340 have excellent wear and durability qualities.
Alloy 4340 can be hardened by a heat treatment followed by an oil quench, or simply by working it while cold. 4340 has average density for a steel alloy, melts at a relatively high temperature (2,600 degrees Fahrenheit) and is malleable enough to be “cold worked,” or worked in a non-heated state. Once it has been annealed it does not need to be worked hot and will retain more elasticity than if it is hardened (heated and quenched in oil). Annealed 4340 has excellent durability.
Due to this increased durability, it is frequently used to make aircraft landing gear, automotive transmission gears and gun parts (all parts that must withstand high pressures or repeated stress).
| Element | Content (%) |
|---|---|
| Iron, Fe | 95.2 – 96.3 |
| Nickel, Ni | 1.7 – 2.0 |
| Chromium, Cr | 0.7 – 0.9 |
| Manganese, Mn | 0.6 – 0.8 |
| Carbon, C | 0.4 – 0.4 |
| Molybdenum, Mo | 0.2 – 0.3 |
| Silicon, Si | 0.2 – 0.3 |
| Sulfur, S | 0.04 |
| Phosphorous, P | 0.04 |
| Properties | Metric | Imperial |
|---|---|---|
| Density | 7.85 g/cm³ | 0.284 lb/in³ |
| Melting point | 1427°C | 2600°F |
| Properties | Metric | Imperial |
|---|---|---|
| Tensile strength | 745 MPa | 108000 psi |
| Yield strength | 470 MPa | 68200 psi |
| Bulk modulus (typical for steel) | 140 GPa | 20300 ksi |
| Shear modulus (typical for steel) | 80 GPa | 11600 ksi |
| Elastic modulus | 190 – 210 GPa | 27557 – 30458 ksi |
| Poisson’s ratio | 0.27 – 0.30 | 0.27 – 0.30 |
| Elongation at break | 22% | 22% |
| Reduction of area | 50% | 50% |
| Hardness, Brinell | 217 | 217 |
Alloy Steel 4340 is used in the following application areas:
- Aircraft Landing Gear
- Power Transmission Gears
- Shafts
- Nuts, Bolts And Pins
- Gun Parts
- Couplings
- Sprockets
- Chucks
- Molds
