Martensitic Stainless 440C is the ring and rolling element steel of the corrosion-resistant version — 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. On a 7300c series angular contact ball bearings that matters because 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. The property data, the comparison against the alternatives and the size table are below.
Why Martensitic Stainless 440C for 7300C Series Angular Contact 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 7300c series angular contact 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 |
Service Limits
A martensitic stainless bearing is rated below the same envelope in chrome steel and it is not stainless in the way 316 is: it is corrosion RESISTANT, and standing salt water, chlorides or long wet periods will still pit it. It is also softer at temperature than GCr15. Take the ratings from the stainless table, and where the environment is genuinely aggressive, consider a full ceramic bearing or a polymer housed unit instead.
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 7300C Series Angular Contact Ball Bearings Available in Martensitic Stainless 440C
| Designation | Bore d (mm) | Outer diameter D (mm) | Width B (mm) | Chamfer r min (mm) | Contact angle a (deg) |
|---|---|---|---|---|---|
| 7300C | 10 | 35 | 11 | 0.6 | 15 |
| 7301C | 12 | 37 | 12 | 1 | 15 |
| 7302C | 15 | 42 | 13 | 1 | 15 |
| 7303C | 17 | 47 | 14 | 1 | 15 |
| 7304C | 20 | 52 | 15 | 1.1 | 15 |
| 7305C | 25 | 62 | 17 | 1.1 | 15 |
| 7306C | 30 | 72 | 19 | 1.1 | 15 |
| 7307C | 35 | 80 | 21 | 1.5 | 15 |
| 7308C | 40 | 90 | 23 | 1.5 | 15 |
| 7309C | 45 | 100 | 25 | 1.5 | 15 |
| 7310C | 50 | 110 | 27 | 2 | 15 |
| 7311C | 55 | 120 | 29 | 2 | 15 |
| 7312C | 60 | 130 | 31 | 2.1 | 15 |
| 7313C | 65 | 140 | 33 | 2.1 | 15 |
| 7314C | 70 | 150 | 35 | 2.1 | 15 |
| 7315C | 75 | 160 | 37 | 2.1 | 15 |
| 7316C | 80 | 170 | 39 | 2.1 | 15 |
| 7317C | 85 | 180 | 41 | 3 | 15 |
| 7318C | 90 | 190 | 43 | 3 | 15 |
| 7319C | 95 | 200 | 45 | 3 | 15 |
| 7320C | 100 | 215 | 47 | 3 | 15 |
