GCr15 Bearing Steel is the steel of the rings and, in most designs, of the rolling elements — the default material for the rings and rolling elements of virtually every standard rolling bearing. On a 600 and 6900 extra small series miniature ball bearings that matters because none of its own — the ground surfaces are bare hardened steel and depend on the lubricant, the seals and the preservative for protection. The property data, the comparison against the alternatives and the size table are below.
Why GCr15 Bearing Steel for 600 and 6900 Extra Small Series Miniature Ball Bearings
The default material for the rings and rolling elements of virtually every standard rolling bearing. In a 600 and 6900 extra small series miniature ball bearings it is the steel of the rings and, in most designs, of the rolling elements.
Through-hardened high-carbon chromium steel is what a raceway is: hard enough to resist the rolling contact stress, clean enough after modern vacuum degassing that the inclusions which start fatigue cracks are rare, and dimensionally stable after tempering so the ground bore stays the size it was ground to.
Material Properties
| Grade designation | GCr15 (GB/T 18254) = 100Cr6 (1.3505) = SAE 52100, through-hardened to 58–64 HRC |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | To about +120 °C as normally heat stabilized; stabilized rings (S1, S2 and above) extend the limit in steps to around +250 °C |
| Corrosion characteristic | None of its own — the ground surfaces are bare hardened steel and depend on the lubricant, the seals and the preservative for protection |
Alternatives and When to Switch
Move to case-hardened steel where the ring section is heavy or the load is shocked; to 440C where the environment is wet or the part must not rust; and to a hybrid bearing with ceramic balls where the speed, the electrical environment or the lubrication regime is beyond what a steel ball will tolerate.
What the Material Changes About the Bearing
The material does not change the envelope: the bore, the outside diameter, the width and the corner radius stay exactly as the boundary dimension standard fixes them, so the bearing is interchangeable with any other bearing of the same designation. What it changes is what happens inside the contact — the fatigue behavior, the tolerance of shock, and the temperature at which the ring stops being dimensionally stable.
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 600 and 6900 Extra Small Series Miniature Ball Bearings Available in GCr15 Bearing Steel
| Designation | Bore d (mm) | Outer diameter D (mm) | Width B (mm) | Chamfer r min (mm) |
|---|---|---|---|---|
| 693 | 3 | 8 | 3 | 0.15 |
| 694 | 4 | 11 | 4 | 0.15 |
| 695 | 5 | 13 | 4 | 0.2 |
| 696 | 6 | 15 | 5 | 0.2 |
| 697 | 7 | 17 | 5 | 0.3 |
| 698 | 8 | 19 | 6 | 0.3 |
| 699 | 9 | 20 | 6 | 0.3 |
| 623 | 3 | 10 | 4 | 0.15 |
| 624 | 4 | 13 | 5 | 0.2 |
| 625 | 5 | 16 | 5 | 0.3 |
| 626 | 6 | 19 | 6 | 0.3 |
| 627 | 7 | 22 | 7 | 0.3 |
| 628 | 8 | 24 | 8 | 0.3 |
| 629 | 9 | 26 | 8 | 0.3 |
| 634 | 4 | 16 | 5 | 0.3 |
| 635 | 5 | 19 | 6 | 0.3 |
| 638 | 8 | 28 | 9 | 0.3 |
