For any questions about our services you can call us at: +86-188-7042-1176
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.
  • Heat Treatment: 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.
CNC machined 4340 steel

Advantages of CNC Machining 4340

Advantage Detailed Description Key Benefit
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.

Technical Parameters & Material Standards

We machine 4340 to meet stringent industrial and aerospace specifications:
Grade Category Specification Characteristics & Ideal Uses
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

  • Machinability: 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.

Application Scenarios

  • 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.
  • Heavy Machinery: Hydraulic rams, rock drill bits, conveyor pins.

Physical Properties Table

Comparison: 4340 vs 4140 (Typical Quenched & Tempered Values):
Property 4340 Alloy Steel 4140 Alloy Steel Unit
Density 7.85 7.87 g/cm³
Tensile Strength 1100 - 1300+ 950 - 1100 MPa
Yield Strength 1000 - 1200 850 - 950 MPa
Izod Impact (Toughness) High Medium -
Hardenability Depth Deep Medium -
Nickel Content 1.65 - 2.00% None -
 
Jucheng Precision Factory
Request Your DFM & Quote – Upload Your Drawings
ㆍFill in your requirements and upload your 2D&3D file, we will feedback your project quotation and DFM within 24 hours.
ㆍFile types: STEP, STP, IGES, IGS, SLDPRT, 3DM, SAT or X_T files File size: < 128 MB Part size: < 1500*1500*1500 mm
ㆍPrivacy: We respect your privacy. Here you can find an example of a non-disclosure agreement. By submitting this form, you agree to our terms & conditions and privacy policy.
Choose File
    Get A Quote And Solution
    Factory Address :
    Shenzhen: Fourth Industrial Zone, Xisha Road, Shajing Street, Baoan District, Shenzhen.
    Dongguan: Building 5 and 4, No. 198, Chang'an Section, Guanchang Road, Chang'an Town, Dongguan.
     
    Sales Office: 
    unit 1, Enterprise City,Durham DL16 6JF, united Kindom
     
     
    +86 - 186 - 8005 - 3076
    project@juchengjm.com
    (Can't open by clicking? Please copy the email address above and email us.)

    Capabilities

    CNC Machining
     
     
    Jucheng Precision ISO 9001, ISO 14001, ISO 13485, IATF 16949

    Resources

    Technical FAQ

    Company

    About Us
    Copyright © 2023 Jucheng Precision All rights reserved.