AMS 6448
AMS 6448 is the SAE Aerospace Material Specification for SAE 6150 chromium-vanadium alloy steel in the bar and forging product forms. The 6150 composition (0.48–0.53% C, 0.80–1.10% Cr, 0.15% V minimum) combines the hardenability of a medium-carbon chromium steel with the grain-refining and carbide-forming benefits of vanadium to produce a material with outstanding resistance to cyclic fatigue loading — the primary design criterion for springs, torsion bars, and highly stressed aerospace shafts. AMS 6448 sets requirements for composition, cleanliness, annealed hardness, and mechanical properties for aerospace-quality 6150 bar and forging stock.
Bar and forging stock to AMS 6448 is primarily used in the annealed or normalized condition for spring coiling, forming, and machining operations, after which heat treatment to 190,000–210,000 psi and shot peening are applied to maximize the fatigue life of the finished component. Shot peening introduces compressive residual stresses at the spring surface that counteract the tensile fatigue stresses applied in service, extending the fatigue life of 6150 springs by a factor of 3–5 compared to unpeened material.
AMS 6448 material heat treated to 190,000–210,000 psi develops the combination of strength and ductility required for spring service: minimum 190,000 psi UTS with minimum 10% elongation and 40% reduction of area, retaining adequate ductility to survive the coiling or bending strains applied during spring manufacture. The vanadium addition provides a fine grain size (ASTM 5 or finer) that is the primary contributor to the superior fatigue crack initiation resistance of 6150 versus plain chromium steels at equivalent strength levels.
- Aircraft coil springs and Belleville washers
- Landing gear spring elements and bump stops
- Helicopter blade root torsion bars
- Aircraft flight control system return springs
- Aerospace valve springs for engine applications
- Drive shaft and transmission torsion springs
AMS 6455 — 6150 Sheet/Strip
6150 Cr-V sheet and strip for formed leaf spring blanks and shaped spring components in aerospace systems.
AMS 6440 — 52100 Bearing Steel Bar
High-carbon bearing steel for rolling contact bearings — maximum hardness to 66 HRC and outstanding contact fatigue life.
Certified Material for Critical Service
AMS 6448 certifications include chemical composition per heat including vanadium content, mechanical properties per lot in the applicable heat treatment condition, grain size (typically ASTM 5 or finer), and inclusion rating per AMS 2301. Spring fatigue testing of sample components is typically performed by the spring manufacturer per the applicable aircraft spring specification to demonstrate design life compliance.