Martensitic Stainless 440C R Series Inch Ball Bearings: The standard corrosion-resistant bearing steel; a stainless bearing is rated below the same envelope in GCr15, so take its load ratings from the stainless table and never from the chrome steel one. The material decides the corrosion behavior — good in water, steam, mild chemicals and food service; it is a hardenable stainless, so it holds less chromium in solution than 304 and will stain in standing chlorides and the temperature the part will stand (about -30 °C to +180 °C in ordinary bearing service, the lubricant usually deciding before the steel does), and it is the reason the alternatives below exist. Properties, limits and the full size table follow.
Why Martensitic Stainless 440C for R Series Inch Ball Bearings
The standard corrosion-resistant bearing steel; a stainless bearing is rated below the same envelope in GCr15, so take its load ratings from the stainless table and never from the chrome steel one. In a r series inch ball bearings it is the ring and rolling element steel of the corrosion-resistant version.
It is the compromise that makes a corrosion-resistant rolling bearing possible: enough carbon to be hardened to a raceway hardness, enough chromium to resist water and mild chemicals. Everything else about the bearing — the envelope, the tolerance class, the clearance group — is unchanged.
Material Properties
| Grade designation | AISI 440C = X105CrMo17 (1.4125), hardened and tempered — the only common stainless hard enough to form a rolling raceway |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | About -30 °C to +180 °C in ordinary bearing service, the lubricant usually deciding before the steel does |
| Corrosion characteristic | Good in water, steam, mild chemicals and food service; it is a hardenable stainless, so it holds less chromium in solution than 304 and will stain in standing chlorides |
Alternatives and When to Switch
If the load matters more than the corrosion, go back to GCr15 with the right seals and a corrosion-inhibiting grease — a sealed chrome steel bearing outlasts a stainless one in many "wet" applications that are only occasionally wet. If the corrosion matters more than the load, go past stainless: a full ceramic or a polymer-housed bearing does not corrode at all.
What the Material Changes About the Bearing
The envelope is unchanged and the bearing drops into the same seat, but the load ratings are not the chrome steel ratings and must not be carried across. Expect a lower rating, a slightly lower temperature ceiling, and — in exchange — a bearing that survives the wash, the condensation or the food process that would rust a standard one.
Fitting a Steel Bearing in an Aluminum Housing
Aluminum has roughly twice the coefficient of thermal expansion of bearing steel, so a housing bore machined to a normal H7 fit at room temperature grows away from the outer ring as the machine reaches operating temperature. The outer ring then turns in its seat and wears the bore. Where the housing is aluminum and the temperature rise is more than about 30 degrees C, tighten the housing fit by one grade — J7 or K7 in place of H7 — or fit a steel sleeve into the aluminum. Check the resulting internal clearance: a tighter housing fit takes clearance out of the bearing, which is often why C3 is specified alongside it.
Sizes of R Series Inch Ball Bearings Available in Martensitic Stainless 440C
| Designation | Bore d (in) | Bore d (mm) | Outer diameter D (in) | Outer diameter D (mm) | Width B (in) | Width B (mm) |
|---|---|---|---|---|---|---|
| R2 | 1/8 | 3.175 | 3/8 | 9.525 | 5/32 | 3.967 |
| R3 | 3/16 | 4.762 | 1/2 | 12.700 | 5/32 | 3.967 |
| R4 | 1/4 | 6.350 | 5/8 | 15.875 | 0.196 | 4.978 |
| R6 | 3/8 | 9.525 | 7/8 | 22.225 | 7/32 | 5.556 |
| R8 | 1/2 | 12.700 | 1-1/8 | 28.575 | 5/16 | 7.938 |
| R10 | 5/8 | 15.875 | 1-3/8 | 34.925 | 5/16 | 7.938 |
| R12 | 3/4 | 19.050 | 1-5/8 | 41.275 | 7/16 | 11.113 |
| R14 | 7/8 | 22.225 | 1-7/8 | 47.625 | 1/2 | 12.700 |
| R16 | 1 | 25.400 | 2 | 50.800 | 1/2 | 12.700 |
| R18 | 1-1/8 | 28.575 | 2-1/4 | 57.150 | 1/2 | 12.700 |
| R20 | 1-1/4 | 31.750 | 2-1/2 | 63.500 | 1/2 | 12.700 |
| R22 | 1-3/8 | 34.925 | 2-3/4 | 69.850 | 9/16 | 14.288 |
| R24 | 1-1/2 | 38.100 | 2-5/8 | 66.675 | 9/16 | 14.288 |
