AMS 6440
AMS 6440 is the SAE Aerospace Material Specification for SAE 52100 high-carbon chromium bearing steel in the bar, wire, forgings, and tubing product forms. SAE 52100 (0.98–1.10% C, 1.30–1.60% Cr) is the world standard through-hardening bearing steel, achieving surface and through-section hardness of 60–66 HRC after austenitizing and oil quenching, with outstanding wear resistance and contact fatigue life in rolling element bearing applications. AMS 6440 sets requirements for chemistry, cleanliness (AMS 2301), spheroidized annealed hardness, and dimensional tolerances for aerospace-grade bearing steel bar and wire.
Aerospace-grade 52100 to AMS 6440 is produced with tightly controlled inclusion ratings per AMS 2301 to minimize the non-metallic inclusions that initiate sub-surface fatigue cracks in rolling contact applications. Premium VAR grades (AMS 6444) provide even higher cleanliness for the most demanding, highest-speed, or longest-life bearing applications in aerospace engine and gearbox systems.
AMS 6440 material is supplied in the spheroidize-annealed condition (207–235 HBW) for machining of bearing rings and ball/roller elements. After machining, components are austenitized at 1475–1525°F (802–829°C), oil quenched, cryogenically treated at -100°F or below to minimize retained austenite, and tempered at 275–350°F (135–177°C) to achieve 60–66 HRC with dimensional stability. The tight carbon-chromium composition produces a fine carbide dispersion in the martensite matrix that provides outstanding wear resistance and load-bearing capacity.
- Aerospace engine ball and roller bearing inner and outer races
- Precision instrument bearings for navigation systems
- Aircraft gearbox rolling element bearings
- Aerospace bearing balls and cylindrical/tapered rollers
- High-speed spindle bearing rings for aerospace manufacturing
AMS 6444 — 52100 Premium Bar
Premium VAR grade 52100 bearing steel with maximum cleanliness for the longest-life and highest-load aerospace bearing applications.
AMS 6448 — 6150 Bar/Forging
Cr-V alloy with outstanding fatigue resistance for aerospace springs, torsion bars, and fatigue-critical shafts.
Certified Material for Critical Service
AMS 6440 certifications include chemical composition per heat, cleanliness per AMS 2301, annealed hardness, dimensional inspection, and eddy current or ultrasonic inspection for bar and wire. For aerospace bearing applications, additional requirements including macro etch, grain size, carbide distribution uniformity, and fatigue life testing are frequently specified by the bearing manufacturer or procurement drawing. Full heat-lot traceability is maintained throughout processing.