Steel 4340 AMS 6409

Steel 4340 AMS 6409 is the aerospace material specification covering 4340 nickel-chromium-molybdenum alloy steel (UNS G43400) bars, forgings, and tubing supplied normalized and tempered to special aircraft-quality cleanliness. It combines the alloy’s deep hardenability and high fatigue strength with a controlled starting condition and tightened inclusion limits for demanding rotating and reciprocating parts.

What defines AMS 6409 within the 4340 bar family is the pairing of a normalized-and-tempered supplied condition with special aircraft-quality cleanliness requirements, verified by magnetic-particle inspection. The N&T condition gives uniform, machinable material with a refined grain structure, while the cleanliness controls raise fatigue reliability above the general air-melt bar spec – without moving to full vacuum remelting.

Typical applications include:

• Crankshafts and connecting rods
• Rotating engine and gearbox shafts
• Highly stressed forged fittings
• Fatigue-loaded pins and couplings

For the same forms supplied normalized and tempered without the special-cleanliness requirement, see the companion specification AMS 6484.

Tech Steel & Materials stocks and supplies AMS 6409 bar, forging, and tubing to aerospace and defense tolerances – request a quote for certified material cut to your size and quantity.