AISI 4340 Round Bar (UNS G43400)
AISI 4340 Round Bar is a high-strength nickel–chromium–molybdenum alloy steel renowned for its exceptional toughness, deep hardenability, and excellent fatigue resistance. This grade maintains high strength even in large cross-sections and is widely used in critical, highly stressed components across aerospace, defense, oil & gas, and heavy engineering industries.
Key Features
- Ni–Cr–Mo alloy steel with very high strength and toughness
- Excellent hardenability and fatigue resistance
- Outstanding performance under shock and dynamic loads
- Good machinability in annealed condition
- Suitable for quenching and tempering to very high strength levels
Equivalent Grades
| Standard | Equivalent Grade |
|---|---|
| EN | 34CrNiMo6 |
| DIN | 1.6582 |
| JIS | SNCM439 |
| BS | 817M40 |
Sizes
- Diameter: 12 mm to 600 mm
- Length: 3 m, 6 m, or cut-to-length
- Custom sizes available on request
AISI 4340 Chemical Composition
| Element | Percentage (%) |
|---|---|
| Carbon (C) | 0.38 – 0.43 |
| Manganese (Mn) | 0.60 – 0.80 |
| Nickel (Ni) | 1.65 – 2.00 |
| Chromium (Cr) | 0.70 – 0.90 |
| Molybdenum (Mo) | 0.20 – 0.30 |
| Silicon (Si) | 0.15 – 0.35 |
| Phosphorus (P) | ≤ 0.035 |
| Sulfur (S) | ≤ 0.040 |
| Iron (Fe) | Balance |
4340 Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 930 – 1080 MPa |
| Yield Strength | 830 – 950 MPa |
| Elongation | 12 – 16% |
| Hardness | 28 – 36 HRC |
UNS G43400 Physical Properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ |
| Melting Point | ~1425°C |
| Thermal Conductivity | 44.5 W/m·K |
| Modulus of Elasticity | 205 GPa |
Types of AISI 4340 Round Bar
- Hot Rolled Round Bar
- Forged Round Bar
- Peeled Round Bar
- Turned & Polished Round Bar
- Quenched & Tempered (Q&T) Round Bar
Applications
- Aircraft landing gear and structural parts
- Heavy-duty shafts, axles, and crankshafts
- Gears, pinions, and couplings
- Oil & gas drilling components
- Defense and aerospace components
- High-stress machine and tooling parts
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