4340 VAR: A Vacuum Arc Remelted, Ultra High Strength Low Alloy Steel
Chemical Definition and Material Class
4340 VAR is a low alloy steel grade that stands out with its high strength, toughness and impact resistance. This steel, to the SAE 4340 standard, is refined by the vacuum arc remelting (VAR) process and thereby acquires an extremely homogeneous structure, free of inclusions and with high fatigue resistance. It is therefore used in critical components in fields requiring high performance, especially aerospace, defence and automotive.
4340 steel is a temperable steel containing nickel, chromium and molybdenum and can reach very high tensile strength by heat treatment. The VAR process increases the microstructural quality and performance consistency of this material.
4340 VAR Standards and Specifications
4340 VAR steel is produced in compliance with the following industry standards:
- AMS 6414 – 4340 VAR, aerospace quality, heat treatable
- ASTM A646 – Vacuum melted low alloy steels
- SAE AMS-S-5000 – Low alloy steel used in high strength aircraft parts
- UNS G43406 – Chemical composition classification
- MIL-S-5000 – Quality control requirements for military applications
4340 VAR Chemical Composition (% by weight, typical values)
Element | Amount (%) |
|---|---|
Carbon (C) | 0.38 – 0.43 |
Manganese (Mn) | 0.60 – 0.80 |
Phosphorus (P) | ≤ 0.025 |
Sulphur (S) | ≤ 0.025 |
Silicon (Si) | 0.15 – 0.30 |
Nickel (Ni) | 1.65 – 2.00 |
Chromium (Cr) | 0.70 – 0.90 |
Molybdenum (Mo) | 0.20 – 0.30 |
Thanks to the VAR process these components have a more consistent distribution, and the mechanical performance of the material becomes more predictable.
4340 VAR Physical and Mechanical Properties
Properties obtained by subjecting it to heat treatment:
- Tensile Strength (UTS): 1080 – 1960 MPa
- Yield Strength (YS): 930 – 1800 MPa
- Elongation (%): 10 – 18
- Toughness (Charpy V-Notch): 20 – 40 J (even at low temperatures)
- Hardness (Rockwell C): 28 – 45 HRC (after heat treatment)
- Density: 7.85 g/cm³
- Modulus of Elasticity: 205 GPa
The desired level of strength and toughness is obtained by applying quenching in oil or polymer and tempering as heat treatment.
Application Areas
4340 VAR steel is used in critical structural parts thanks to its extraordinary fatigue strength and impact toughness. Its principal areas of use are given below:
1.Aerospace Industry
#Landing gear shafts
#Propeller shafts and rotor shafts
#Piston rods, fasteners
#Jet engine parts (at a secondary level)
2.Defence and Ballistic Systems
#Armoured vehicle shafts
#Fittings for gun and rocket systems
#Barrels and highly stressed weapon parts
3.Automotive and Motorsport
#High performance crankshafts
#Differential shafts
#Racing car suspension parts
4.Energy and Industrial Machinery
#Turbine shafts
#Gear systems and highly stressed connections
#Oil and gas drilling systems
Advantages
- High Fatigue Resistance: The fatigue life is very high, especially with the reduction of internal defects after the VAR process.
- Excellent Impact Toughness: It provides high impact absorption even at low temperatures.
- Suitability for Heat Treatment: Hardness and strength can be adjusted over a broad range.
- Homogeneous Microstructure: Thanks to the VAR process the inclusions it contains are reduced, and strength and toughness become more stable.
- Welding and Machinability: Suitable machinability before heat treatment, high performance after tempering.
Disadvantages
- High Cost: The VAR process is a costly process; the cost compounds especially in large section parts.
- Corrosion Resistance Is Poor: It is not as corrosion resistant as stainless steel; coating or lubrication is required.
- Heat Treatment Requirement: The final strength is provided by heat treatment; incorrect application may weaken the mechanical properties.
- Magnetic Property: It is magnetic; in some applications this may be a disadvantage.
Conclusion and Engineering Evaluation
4340 VAR offers a top level solution in terms of reliability, strength and life performance in the production of critical structures and mechanical parts requiring high performance. Despite its high cost, it is preferred especially in fields where the tolerance for error is low, such as the aerospace, defence and racing industry.
The micro-cleanliness that the VAR process brings increases the fatigue life and impact resistance of the material. For this reason 4340 VAR is not merely an alloy but a solution partner for high engineering requirements.
#4340VAR
#AMS6414
#AMS6454
#AMS6484
#ASTMA646
#SAEAMS-S-5000
#UNSG43406
#MIL-S-5000
AMS 6414 — we supply 4340 VAR
4340 VAR (UNS G43400 / equivalent to 1.6565) is a high strength low alloy steel produced by vacuum arc remelting. In aerospace and defence applications it is used to the AMS 6414, AMS 6454 and AMS 6484 standards.
It is supplied certified, in the dimensions and forms required. Request a quotation for stock availability, the dimension list and pricing.
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