300M (4340 MOD) Alloy Steel - AMS 6417 - UNS K44220

300M Consumable Electrode Vacuum Remelted Steel is 4340 Alloy Steel modified with the addition of Vanadium and higher Silicon. Carbon Content in AMS 6417 Carbon content is 0.37% to 0.43”. Specifications AMS 6419 requires 0.40” – 0.45% C and AMS 6256 0.40% - 0.44%C. Service Steel Aerospace stocks material with restricted carbon content to certify chemistry to these various specifications.

300M Alloy Steel Bars
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These chemistry modifications provide an Alloy Steel with very good fatigue strength, ductility, impact strength and fracture toughness. 300M is widely used for Aircraft Landing Gear.

300M (4340 Mod) Alloy Steel Applications:

This grade is used high strength structural applications with sections 3.5” in and under in cross-section thickness for through-hardness requiring minimum Rockwell C hardness 52 HRC that are subject to exacting magnetic particle inspection standards. Applications include:

  • Aircraft Landing Gear
  • Airframe Parts, such as Flap Tracks
  • Missile Components
  • Motorsport Applications

Common Trade Names:


  • Lescalloy 300M Vac-Arc
  • 4340 Modified
  • 434M
  • 300M CEVM

Common Specifications:


  • AMS 6417 (Replaces MIL-S-83135)
  • AMS 6419
  • AMS 6257 (Replaces MIL-S-8844 REV D CLASS 3)
  • AMS 2300 Premium Aircraft Quality Cleanliness
  • BMS 7-26
  • BE1036
  • CE-0896
  • C-05-1190
  • DMS 1935
  • GM1012
  • MTL 1201
  • S155
  • MAT 137
  • SAE 434M
  • IGQ 41-11
  • LAT 1.9042
  • ZFNL 9207
  • ASTM A646

Physical Properties:


  • Density: 0.2836 #/in3

Stocked Sizes:


Note: Stocked as Normalized & Tempered (N&T)
  • Rounds: Rough Turned (RT) N&T:
    • 40 Diameters 0.500" through 11"
  • Blocks (Bars): Forged, Machined 4 sides N&T
    • Stocked sizes
      • 8" x 12" and 12" x 23"
      • Custom thicknesses & widths available saw-cut

Chemical Composition:


SymbolElementMin %Max %
CCarbon0.38%0.43%
MnManganese0.65%%0.90%
SiSilicon1.45%1.80%
PPhosphorus0.010%
SSulfur0.008%
CrChromium0.70%0.95%
NiNickel1.65%2.00%
MoMolybdenum0.30%0.50%
VVanadium0.05%0.10%
CuCopper0.35%
Carbon Content Note:
Both AMS 6257 and AMS 6419 require minimum 0.40% Carbon content
SSA material is stocked with minimum 0.40% Carbon content to meet multiple specifications

AMS 6417 Macrostructure standards:


ClassConditionSeverity
1FrecklesA
2White SpotsA
3Radial SegregationB
4Ring PatternB

Minimum Longitudinal Tensile Properties per AMS 6417:


PropertyValue
Tensile Strength270 ksi
Yield Strength 0.2% offset220 ksi
Elongation8%
Reduction of Area30%
After heat treating specimens per paragraph 3.4.4

Minimum Transverse Tensile Properties per AMS 6417:


Cross-section Area Tensile StrengthYield Strength 0.2% OffsetAvg. Reduction of AreaIndividual Reduction of Area
Up to 100 in2, incl270 ksi220 ksi30%25% min
Over 100 in2 to 144 in2, incl270 ksi220 ksi25%20% min
Over 144 in2 to 225 in2, incl270 ksi220 ksi20%15% min
Over 225 in2270 ksi220 ksi15%10% min

AMS 6417 Heat Treatment


Type of Heat TreatingProcess
Normalize1700° F +/- 25° F (927° C +/- 14° C), then air cool
Harden1600° F +/- 25° F (871° C +/- 14°C), quench in oil
TemperDouble temper 400° – 1200° F (204° – 649° C) depending on desired strength and hardness.

AMS 6417 Fabrication


ForgingForge between 1950° – 2250° F (1066° – 1232° C), min 1700° F
MachinabilityNormalize, then temper at approx. 1200° F (649° C) for optimum condition for machining
WeldingCan be welded by gas or arc fusion methods.

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