M50 is a vacuum melted, high speed tool steel type bearing alloy that holds hardness at the temperatures found inside aircraft engine bearings. Its molybdenum, chromium and vanadium carbides give the hot hardness and rolling contact fatigue life that mainshaft bearings require.
M50 NiL is the case carburizing derivative: a low carbon, nickel bearing core that stays tough and crack resistant carries a hard carburized case, which is the usual answer where a bearing race must tolerate hoop stress and damage tolerance requirements.
Both are stocked as bar and forging billet, produced VIM-VAR, with melt traceability and inspection to the applicable bearing quality requirements.
Sizes and stock
- Wire: through .385" DIA
- Round bar: through 8" DIA
- Custom shapes and forgings: per request
Processing capabilities
- Vacuum melted (VAR / VIM-VAR) stock with full melt traceability
- Normalize, anneal, quench and temper to the ordered condition
- Saw cutting, trepanning, gun drilling and rough machining
- Magnetic particle and ultrasonic inspection to AMS 2301 / AMS 2154 on request
Specifications
Material is released to the applicable specification with mill test reports and, on request, independent lab verification.
Why engineers specify M-50
- Retains hardness at elevated bearing operating temperature
- Excellent rolling contact fatigue life
- Vacuum induction melted and vacuum arc remelted for cleanliness
- M50 NiL available where a tough, damage tolerant core is required
Nominal chemistry
Percent by weight, nominal composition per the governing specification. The mill test report for your heat is the controlling document.
Typical mechanical properties
| Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| Annealed | - | - | - | ~255 HBW max |
| Hardened and tempered | - | - | - | 60-64 HRC |
Typical published values for reference only, not for design. Properties vary with section size, product form and processing. Order to the specification and condition your drawing requires.
Typical applications
- Aircraft engine mainshaft bearings, races and rolling elements
- Gearbox bearings in high temperature service
- Precision spindle bearings
Fabrication notes
Machining
Best machined in the annealed or normalized-and-tempered condition, then heat treated to final strength. Rough machining before hardening, with a finish pass after temper, controls distortion on long or thin sections. We can supply rough turned, trepanned or gun drilled stock so your first operation starts closer to net shape.
Welding
Weldable with low hydrogen practice, preheat appropriate to carbon equivalent and section size, and a post weld stress relief or full re-heat treat. For high strength conditions the weld and heat affected zone should be re-treated to restore properties.
Forming
Hot work in the annealed condition. Cold forming is limited at high hardness, so bend and form before hardening and follow with stress relief where the geometry is tight.
M-50 compared with similar grades
52100
Lower cost bearing steel without the hot hardness needed above roughly 350F.
M50 NiL
Case carburized version with a tough low carbon core for damage tolerant races.
Designations and cross reference
- Material family
- Alloy Steels
Working from an obsolete, foreign or superseded designation? Send it over and we will cross reference it to a current grade and specification.
Quality, testing and traceability
Supplied aircraft quality with mill test reports, melt and heat traceability, and, on request, magnetic particle inspection to AMS 2301 or AMS 2300, ultrasonic inspection to AMS 2154, chemical assay, hardness and full mechanical testing.
We are AS9100D and ISO 9001:2015 registered. If our stock does not already carry the inspection your specification requires, we can quote the material with that work performed. More on our quality system
Available forms
Custom sizes converted from billet, plus saw cut, waterjet and near-net blanks. See custom conversions
M-50 frequently asked questions
What is M-50?
M50 is a vacuum melted, high speed tool steel type bearing alloy that holds hardness at the temperatures found inside aircraft engine bearings. Its molybdenum, chromium and vanadium carbides give the hot hardness and rolling contact fatigue life that mainshaft bearings require.
What forms is M-50 available in?
We supply M-50 in wire, bar, forging. Custom sizes are converted from billet, and we can provide saw cut, waterjet or near net blanks so material arrives closer to your finished part.
What specifications can M-50 be supplied to?
Commonly ordered specifications include AMS 6490, AMS 6491. Material is released to the specification and condition on your purchase order, with mill test reports supplied as standard.
What conditions can M-50 be ordered in?
We can supply Annealed, Hardened and tempered. If our stock is not already in the condition you need, we can quote it with the heat treatment performed before shipment.
Can you cut M-50 to size?
Yes. Saw cutting, waterjet, laser and shearing are available, along with trepanning, gun drilling, lathe turning and CNC machining, so you can order blanks or rough machined pieces rather than full lengths.
Do you provide test reports and additional testing on M-50?
Every order ships with mill test reports and heat traceability. If your print calls for ultrasonic inspection, penetrant dye, magnetic particle, chemical assay, micrography, hardness or mechanical testing and our stock does not already carry it, we can quote the material with that work performed.
Can M-50 be supplied to DFARS domestic melt requirements?
Tell us at quote stage if the order is DFARS or domestic melt restricted and we will confirm availability against that requirement before you commit.
What do you need to quote M-50?
Grade, form, dimensions, quantity, specification and condition, plus any testing or certification requirements and the date you need it. Send a drawing if you have one. Quotes are typically ready within 24 hours.
How does M-50 compare with 52100?
Lower cost bearing steel without the hot hardness needed above roughly 350F.