Steel M-50 AMS 6491

AMS 6491 is the aerospace material specification covering M-50 bearing steel bars, forgings and tubing, made to premium aircraft quality for bearing applications by double vacuum melting. It’s the cleanest form of M-50 you can buy, and the standard for the most critical rotating bearings in modern gas turbine engines.

What defines AMS 6491 is its two-stage VIM-VAR melting. The steel is first vacuum induction melted, which refines the chemistry and removes gases before the ingot is cast. It’s then vacuum arc remelted to break up and float out the remaining oxide inclusions. Carbon is held to a tighter 0.80-0.85%, giving more consistent hardness and carbide structure from heat to heat. The result is the longest and most predictable rolling-contact fatigue life of any M-50, which is why engine makers specify it for bearings that can’t be allowed to fail.

Typical AMS 6491 uses:

• Main-shaft ball and roller bearings in turbofan and turboshaft engines
• Helicopter transmission and rotor-drive bearings
• High-speed spacecraft and turbopump bearings
• Any bearing where the drawing requires double vacuum melted cleanliness

Where single vacuum arc remelted quality is enough, see the companion specification AMS 6490. Full composition, heat-treat and property data are on the M-50 bearing steel page. Tech Steel & Materials stocks and supplies AMS 6491 bar, forgings and tubing to aerospace and defense tolerances. Request a quote for certified, traceable material cut to your size and quantity.