4340 ALLOY STEEL – AMS 6414 VAR – UNSG43406
4340 VAR AMS 6414 is a low alloy Chromium-Nickel-Molybdenum steel capable of being heat treated to high strength levels.
This specification is for a premium aircraft-quality, low-alloy steel in the form of bars, forgings, mechanical tubing, and forging stock. Service Steel Aerospace stocks Premium Aircraft Quality produced double melted in an Electric Furnace, followed by VAR, or Vacuum Arc Remelt (also known as CEVM, or Consumable Electrode Vacuum Arc Remelting). This results in a much cleaner steel meeting the magnetic particle test requirements of AMS-2300.
It is a steel of the highest quality with excellent transverse ductility and toughness at high strength levels. It has good shock and impact resistance as well as wear and abrasion resistance in the hardened condition. Standard Aircraft Quality air-melted AMS 6414 Air Melt material is available on request. 4340 ESR, or Electroslag Remelted material is also available on request.
4340 alloy steel applications:
4340 has been used typically for parts requiring a through-hardening capability up to 3.5 inches (89 mm) in nominal thickness at time of heat treatment and subject to rigid magnetic particle inspection standards, but usage is not limited to such applications. Premium Aircraft Quality is intended for use in the manufacturing of highly stressed parts at higher strength levels, such as 260/280,000 psi and where a much cleaner steel is desired.
Chemical Composition:
| Symbol | Element | Min % | Max % |
| C | Carbon | 0.38% | 0.43% |
| Mn | Manganese | 0.65% | 0.90% |
| Si | Silicon | 0.15% | 0.35% |
| P | Phosphorus | 0.01% | |
| S | Sulfur | 0.01% | |
| Cr | Chromium | 0.70% | 0.90% |
| Ni | Nickel | 1.65% | 2.00% |
| Mo | Molybdenum | 0.20% | 0.30% |
| Cu | Copper | 0.35% |
Mechanical Properties:
| Bar Size | Temperature * | Tensile Strength | Yield Strength | Elongation in 2″ | Reduction of Area |
| 3.5″ Dia. | 400° F (204° C) | 276 ksi | 222 ksi | 11.0% | 35.0% |
| 7.5″ Dia. | 500° F (260° C) | 265 ksi | 222 ksi | 8% | 25.0% |
| 10.5″ Dia. | 1100° F (593° C) | 165 ksi | 150 ksi | 18% | 60.0% |
* After Normalized 1650°/1700° F, Austenized 1500°/1525° F, Oil quenched
Common Trade Names:
Lescalloy 4340 Vac-Arc
European Designation 36CrNiMo4
4340 Chrome-Nickel-Molybdenum Steel
SAE 4340
AISI 4340
4340 CEVM
4340 ESR
4340 VAR AMS 6414 Common Specifications:
AMS 6414 VAR (CEVM)
AMS 6414 ESR
AMS 6415 (Air Melt)
AMS 6409
MIL-S-5000, AMS-S-5000 (Both are cancelled and superseded by AMS 6415)
MIL-S-8844
299-947-055 Bell Helicopter
SS 9702 Sikorsky
DMS 1555 Boeing (Previously McDonnell Douglas)
HMS 6-1121 (for 4340 ESR Only)
BPS 4807 (for 4340 ESR Only)
