AMS 6322
AMS 6322 is the SAE Aerospace Material Specification for SAE 8740 nickel-chromium-molybdenum alloy steel in the bar, forging, and mechanical tubing product forms. The 8740 composition (0.38–0.43% C, 0.40–0.70% Ni, 0.40–0.60% Cr, 0.20–0.30% Mo) — with slightly higher molybdenum than SAE 8620 — provides greater hardenability and through-hardening depth in medium sections, making it suitable for both carburizing and through-hardening applications in aerospace production. In the Q&T condition, 8740 achieves 130,000–180,000 psi tensile strength with good ductility and machinability.
AMS 6322 bar stock is widely used for aerospace bolt and fastener production (AN and NAS standard bolts are frequently manufactured from 8740) in addition to gear blanks, shafts, and structural fittings. Its consistent response to heat treatment, excellent machinability in the annealed condition, and well-characterized properties in the aerospace supply chain make it one of the most prevalent medium-strength alloy steels for aerospace hardware production.
SAE 8740 to AMS 6322, when Q&T to 180,000 psi, achieves minimum 180,000 psi UTS, 163,000 psi yield strength, 12% elongation, and 45% reduction of area. For bolt production at 160,000 psi (AN bolt strength), elongation increases to 14% with 50% reduction of area. Induction hardening of shaft journals and gear teeth is readily applied to 8740 after core heat treatment, achieving surface hardness of 58–62 HRC while maintaining the specified core strength and toughness.
- AN and NAS standard aircraft bolts and fasteners
- Aircraft transmission gears and pinions (carburized)
- Aerospace shaft and axle stock
- Hydraulic manifold bodies and structural fittings
- Aircraft clevis pins and structural fastener bodies
- Carburized piston pins and bearing journals
Certified Material for Critical Service
AMS 6322 certifications include chemical composition per heat, mechanical properties per lot in the applicable heat treatment condition (with specific property requirements for the bolt and fastener and gear/shaft conditions), grain size, and inclusion rating per AMS 2301. Bolt stock must additionally meet head-forming, grain flow, and surface quality requirements per the applicable bolt specification (AN, NAS, or MS). Full heat-lot traceability is maintained through the fastener supply chain.