AMS 6381
AMS 6381 is the SAE Aerospace Material Specification for SAE 4140 chromium-molybdenum alloy steel in the bar, forging, and mechanical tubing product forms. It covers round, square, hexagonal, and flat bar in diameters and thicknesses from 0.375 inch through 14.000 inches in the annealed, normalized, or quenched and tempered condition. AMS 6381 specifies chemical composition (0.38–0.43% C, 0.80–1.10% Cr, 0.15–0.25% Mo), mechanical properties, cleanliness, and certification requirements for aerospace-quality 4140 bar and forging stock.
Bar and forging stock to AMS 6381 is one of the most broadly purchased alloy steel specifications in the aerospace supply chain. The combination of high achievable strength (up to 200,000 psi), excellent hardenability, machinability, and consistent heat treatment response makes 4140 bar the standard material for aerospace bolt blanks, hydraulic actuator rod stock, shaft blanks, and structural fitting forgings across virtually all aircraft and missile programs.
AMS 6381 material heat treated to the 200 ksi (1380 MPa) condition achieves minimum UTS of 200,000 psi, minimum 0.2% yield strength of 181,000 psi, minimum 10% elongation, and minimum 35% reduction of area. Charpy V-notch impact energy in this condition is typically 20–40 ft-lb at room temperature. Full hardenability through 2-inch diameter bar stock is achieved with the 4140 Cr-Mo composition when oil quenched. For larger cross-sections above 3 inches, restricted hardenability H-band grades per ASTM A304 should be considered.
- High-strength aerospace bolt and fastener blanks
- Hydraulic actuator piston rod stock
- Aerospace shaft and spindle blanks
- Aircraft structural fitting and bracket forgings
- Ordnance component bodies and housings
- Landing gear secondary structure machined components
AMS 6382 — 4140 Sheet/Plate
4140 sheet, strip, and plate for structural housings, brackets, and machined fittings requiring higher strength than 4130 flat products.
AMS 6415 — 4340 Air Melt Bar
Ni-Cr-Mo 4340 bar and forging for primary aircraft structural applications at 200–260 ksi.
Certified Material for Critical Service
AMS 6381 certifications include chemical composition per heat, mechanical properties per lot (tensile, yield, elongation, reduction of area), cleanliness rating per AMS 2301, and ultrasonic inspection per AMS 2631 where specified. Material is traceable from mill melt through bar processing by heat and lot number. For bolt manufacture, bar stock must additionally comply with the applicable bolt specification regarding grain flow and head-forming requirements.