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AMS 6444 is the premium-grade SAE Aerospace Material Specification for SAE 52100 high-carbon chromium bearing steel in bar and forging forms, produced to tighter cleanliness requirements than the standard AMS 6440 grade. The premium cleanliness requirements of AMS 6444 — achieved through vacuum arc remelting (VAR) or other approved premium melt processes — minimize non-metallic inclusions to levels significantly below those of AMS 6440 air-melt bar, directly extending bearing fatigue life in rolling contact applications where sub-surface inclusion-initiated fatigue is the life-limiting failure mode.
AMS 6444 is specified for aerospace engine bearings, gearbox bearings, and other high-speed, high-load rotating machinery bearings where bearing fatigue life and reliability are critical to aircraft safety. The investment in VAR-quality 52100 versus standard AMS 6440 is justified wherever extended fatigue life, reduced bearing size for weight savings, or increased design certainty are required in the aerospace bearing application.
AMS 6444 material is produced by VAR processing to achieve oxygen and sulfur levels significantly below those of air-melt grades, reducing the density of oxide and sulfide inclusions that initiate rolling contact fatigue spalls. The same heat treatment procedure as AMS 6440 applies (austenitize, oil quench, cryogenic treat, low temper), achieving 60–66 HRC. In comparative rolling contact fatigue tests, VAR-quality 52100 demonstrates 3–5× longer L10 fatigue life versus air-melt equivalents at identical loads and speeds in precision bearing test machines.
- Aerospace turbine engine main shaft bearings
- High-speed helicopter gearbox rolling element bearings
- Precision instrument bearings requiring maximum fatigue life
- Aerospace actuator and flight control surface bearings
- High-reliability bearing races for military and space applications
Certified Material for Critical Service
AMS 6444 certifications include chemical composition per heat, VAR melt process documentation, cleanliness per AMS 2300 (more restrictive than AMS 2301), annealed hardness, dimensional inspection, and non-destructive inspection. For aerospace turbine engine bearing applications, bearing manufacturers typically impose additional requirements including grain size, carbide band uniformity, macro etch, and lot acceptance testing. Full traceability by VAR heat and lot is maintained through all processing steps.