AISI 4340 Alloy Steel CNC Machining Material
When structural failure is not an option, AISI 4340 is the go-to alloy steel. Distinguished by its significant Nickel content, this Nickel-Chromium-Molybdenum alloy offers superior toughness and ductility compared to 4140, even at extremely high strength levels. Its defining characteristic is deep hardenability, meaning it retains its mechanical properties throughout the cross-section of massive parts, not just on the surface. At JUCHENG, we specialize in machining heavy-duty 4340 components for the aerospace and oil & gas sectors, handling everything from large forged blocks to precision-turned shafts.
4340 Alloy Steel
JUCHENG's 4340 Machining Capabilities
Processing this tough, high-nickel alloy requires robust machinery. We offer:
- Heavy Turning: We utilize high-rigidity CNC lathes to turn large diameter 4340 shafts and axles, maintaining tight runout tolerances over long lengths.
- Hard Milling: We can machine 4340 in pre-hardened states or finish-machine after heat treatment to correct any distortion.
- Wärmebehandlung: We provide precise Quench and Temper (Q&T) cycles to unlock the full potential of 4340, achieving tensile strengths exceeding 1500 MPa.
- NDT Inspection: For critical aerospace parts (like landing gear components), we offer Non-Destructive Testing (Magnetic Particle or Ultrasonic) to ensure the internal integrity of the raw material and machined part.
Advantages of CNC Machining 4340
| Vorteil | Detaillierte Beschreibung | Hauptvorteil |
| Deep Hardenability | Achieves uniform hardness/strength from the surface to the core, even in parts >100mm thick. | Critical for large shafts, axles, and heavy-section components where 4140 might have a soft core. |
| Superior Toughness | Excellent resistance to shock and impact, even at high hardness levels. | Ideal for landing gear, impact tools, and rock-crushing machinery. |
| Fatigue Resistance | Outstanding fatigue life under cyclic loading. | Reliable for crankshafts and power transmission components. |
| Heat Resistance | Retains strength at elevated temperatures better than standard carbon steels. | Suitable for engine components and high-friction environments. |
| Ductility | Maintains good ductility relative to its high strength. | Resists brittle fracture under extreme stress. |
Technische Parameter & Materialnormen
We machine 4340 to meet stringent industrial and aerospace specifications:
| Güteklasse | Spezifikation | Eigenschaften & Ideale Verwendungen |
| AISI 4340 (Annealed) | Soft State | Characteristics: Delivered in a normalized/annealed state. Machinability is decent. Must be heat treated after machining for final use. Uses: Complex structural parts requiring significant material removal. |
| AISI 4340 (Q&T) | Quenched & Tempered | Characteristics: Heat treated to high strength (e.g., 34-40 HRC). Tough to machine but provides immediate performance. Uses: Heavy-duty power transmission gears, shafts, fasteners. |
| AMS 6415 / 6484 | Aerospace Grade | Characteristics: Premium quality (often Vacuum Arc Remelted - VAR) for maximum cleanliness and fatigue life. Uses: Aircraft landing gear, critical flight safety hardware, rotor shafts. |
CNC Machining Guidelines 4340
- Zerspanbarkeit: 4340 is tougher and "gummier" than 4140 due to the nickel content. We use slower cutting speeds and rigid setups to prevent chatter.
- Coolant: Essential. High heat generation can cause work hardening. We use high-lubricity coolant to improve surface finish.
- Welding: Very Difficult. 4340 has high hardenability and is prone to cracking during welding. It requires strict pre-heating and post-weld stress relief. We generally advise against welding 4340.
- Finishing: Grinding is often used as a final step for hardened 4340 journals or bearing surfaces to achieve Ra 0.4 or better.
Anwendungsszenarien
- Aerospace: Landing gear struts, helicopter rotor hubs, transmission gears.
- Automotive (Racing): High-performance crankshafts, connecting rods, axle shafts.
- Oil & Gas: Downhole drilling jars, heavy-duty valves, large fasteners.
- Schwermaschinen: Hydraulic rams, rock drill bits, conveyor pins.
Tabelle der physikalischen Eigenschaften
Comparison: 4340 vs 4140 (Typical Quenched & Tempered Values):
| Eigenschaft | 4340 Alloy Steel | 4140 Alloy Steel | Einheit |
| Dichte | 7.85 | 7.87 | g/cm³ |
| Zugfestigkeit | 1100 - 1300+ | 950 - 1100 | MPa |
| Streckgrenze | 1000 - 1200 | 850 - 950 | MPa |
| Izod Impact (Toughness) | High | Medium | - |
| Hardenability Depth | Deep | Medium | - |
| Nickel Content | 1.65 - 2.00% | None | - |
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