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 Steel Round Bar
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Service Steel Aerospace is one of the largest distributors / suppliers of 4340 Alloy Steel available in several forms including round bar, flat bar, and square bar as well as block, and billet. See below for product size ranges stocked.

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.

4340 VAR AMS 6414 Common Specifications:

  • AMS 6414 VAR (CEVM)
  • AMS 6414 ESR
  • AMS 6415 (Air Melt)
  • MIL-S-5000, AMS-S-5000 (Both are cancelled and superseded by AMS 6415)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)
  • Common Trade Names:

  • Lescalloy 4340 Vac-Arc
  • European Designation 36CrNiMo4
  • Common OEM Approvals:

  • Bell Helicopter
  • Boeing
  • Bombardier
  • Pratt Whitney LCS
  • Sikorsky
  • 4340 VAR AMS 6414 Stocked Sizes:

  • Rounds: 39 sizes 0.500” through 10.00” diameter
  • Flats & Blocks: 12" x 23" block to cut-to-size”
    • - Custom thicknesses & widths available saw-cut
  • Billets: 7” and 14" billet for conversion to special sizes

    • Note: Stocked as Normalized and Tempered

    4340 Air Melt AMS 6415 Stocked Sizes:

  • Rounds: 35 sizes 0.500” through 8.500” diameter
  • Chemical Composition:

    SymbolElementMin %Max %

    Physical Properties:

  • Density: 0.2836 #/in3
  • Grain Size 5 or finer
  • Macrostructure limits:

    2White SpotsA
    3Radial SegregationB
    4Ring PatternB

    Hardenability Requirements:

  • Jominy: J 12/16 inch: 53 RC Hardness min
  • Jominy: J 20/16 inch: 32 RC Hardness min

  • For Material Normalized 1600° F (871° C) with Test Specimen Austenitized 1550° F (843° C)

    Heat Treatment:

    Normalize1600° - 1700° F (871° – 927° C), then air cool
    Auestenitize1475° – 1575° F (802° – 857° C), then quench in oil
    Temper400° – 1200° F (204° – 649° C) depending on desired strength. For Ultimate Tensile Strength above 260ksi, temper between 400° – 500° F (204° – 260° C)

    Tempering Data:

    TemperatureHardness (approx)
    400° F (204° C)52 HRC
    500° F (260° C)49 HRC
    600° F (316° C)47 HRC
    700° F (371° C)45 HRC
    800° F (427° C)41 HRC
    900° F (482° C)38 HRC
    1000° F (538° C)35 HRC
    1100° F (593° C)30 HRC
    1200° F (649° C)25 HRC

    After Austenitized 1550° F (843° C), quenched in oil, Twice-tempered (2 hours each)


    ForgingForge between 1950° – 2250° (1066° – 1232° C). Preheating or furnace cooling in ash or lime is recommended
    MachinabilityNormalize, then temper at approx. 1200° F (649° C) for optimum condition for machining
    WeldingCan be welded by gas or arc fusion methods. Alloy is capable of air hardening, and should be either Annealed or Normalized and Tempered after welding

    Minimum Longitudinal Tensile Properties:

    Tensile Strength260 ksi
    Yield Strength 0.2% offset217 ksi
    Reduction of Area30%

    After heat treating specimens per paragraph 3.4.6

    Mechanical Properties:

    Bar SizeTemperature * Tensile StrengthYield Strength Elongation in 2"Reduction of Area
    3.5" Dia.400° F (204° C)276 ksi222 ksi11.0%35.0%
    7.5" Dia.500° F (260° C)265 ksi222 ksi8%25.0%
    10.5" Dia.1100° F (593° C)165 ksi150 ksi18%60.0%

    * After Normalized 1650°/1700° F, Austenized 1500°/1525° F, Oil quenched