4340 (E4340) Alloy Steel

About 4340 (E4340) Alloy Steel

AISI 4340 (E4340) alloy steel is a medium carbon, low alloy steel known for its toughness and strength. Machining is done typically in the annealed condition. 4340 steel properties offer good ductility in the annealed condition, allowing it to be bent or formed. Fusion and resistance welding is also possible with our 4340 steel from stock.

4340 steel alloy is used primarily for structural applications such as aircraft landing gears. 4340 alloy steel is also used in the manufacturing of structural parts like gears, sprockets, chucks, molds, and more.

As one of the most focused suppliers of 4340 steel in the U.S., Benedict-Miller maintains one of the largest stocked inventories of aircraft quality (AQ) steel.

SAE 4340 Steel Specification: Typical Chemical Properties (%)

Carbon 0.38/0.43 Sulfur 0.025 max. Molybdenum 0.20/0.30
Manganese 0.65/0.85 Silicon 0.15/0.35 Nickel 1.65/2.00
Phosphorus 0.025 max. Chromium 0.70/0.90 Copper 0.35 max.

Above chemistry applies to all 4340 (E4340) Plate Specifications (AMS 6359) - Annealed, AMS 6415 Round Bar Cold Finished- Annealed, AMS 6415 Round Bar Hot Rolled- Annealed.


About AMS 6415 Round Bar
(Cold Finished, Hot Rolled)

AMS 6415 round bar cold finished or hot rolled steel 4340 is one of the richer alloy steels, featuring hardenability with high strength characteristics. This steel is an excellent choice for highly stressed parts intended to operate under severe conditions. 4340 steel round bar is used for crankshafts, landing gear struts, valves, connecting rods, axle shafts, machine tool arbors, and more.

Learn more by visiting our 4340 per AMS 6415 CF and HR bar pages.


About AMS 6359 Plate (Hot Rolled)

As one of the most focused 4340 steel suppliers in the U.S. your search ends here. 4340 steel plate from Benedict-Miller, LLC all meets aircraft quality standards. Circles, rounded plate (plate rounds) or flat bar can all be cut in house from our 4340 plate in stock. Note: 4340 steel flat bar is not extruded bar but is often fit for function.

Learn more by visiting our 4340 per AMS 6359 Plate pages.



  • Largest stocked inventory for fast delivery
  • Prime stock only, highest quality for reliability, durability
  • Sheet, Plate, or Round Bar
  • AMS certified
  • DFARS compliance
  • Domestic material
  • Single Source Solution
  • Precision parts cut to your specifications using DXF files
  • ISO Certified
  • No minimum quantities


Representing Only Prime Stock from World Class U.S. Mills


Supplying the world AISI 4130 (E4130) and 4340 (E4340) Aircraft Quality Steel.
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