Martensitic Stainless 440C 7200B 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. 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 7200B 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 7200b 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.
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.
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 7200B 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) |
|---|---|---|---|---|---|
| 7200B | 10 | 30 | 9 | 0.6 | 40 |
| 7201B | 12 | 32 | 10 | 0.6 | 40 |
| 7202B | 15 | 35 | 11 | 0.6 | 40 |
| 7203B | 17 | 40 | 12 | 0.6 | 40 |
| 7204B | 20 | 47 | 14 | 1 | 40 |
| 7205B | 25 | 52 | 15 | 1 | 40 |
| 7206B | 30 | 62 | 16 | 1 | 40 |
| 7207B | 35 | 72 | 17 | 1.1 | 40 |
| 7208B | 40 | 80 | 18 | 1.1 | 40 |
| 7209B | 45 | 85 | 19 | 1.1 | 40 |
| 7210B | 50 | 90 | 20 | 1.1 | 40 |
| 7211B | 55 | 100 | 21 | 1.5 | 40 |
| 7212B | 60 | 110 | 22 | 1.5 | 40 |
| 7213B | 65 | 120 | 23 | 1.5 | 40 |
| 7214B | 70 | 125 | 24 | 1.5 | 40 |
| 7215B | 75 | 130 | 25 | 1.5 | 40 |
| 7216B | 80 | 140 | 26 | 2 | 40 |
| 7217B | 85 | 150 | 28 | 2 | 40 |
| 7218B | 90 | 160 | 30 | 2 | 40 |
| 7219B | 95 | 170 | 32 | 2.1 | 40 |
| 7220B | 100 | 180 | 34 | 2.1 | 40 |
