In a uc300 series insert bearings, GCr15 Bearing Steel is the steel of the rings and, in most designs, of the rolling elements. The grade is GCr15 (GB/T 18254) = 100Cr6 (1.3505) = SAE 52100, through-hardened to 58–64 HRC; it is magnetic, and its usable service range is to about +120 °C as normally heat stabilized; stabilized rings (S1, S2 and above) extend the limit in steps to around +250 °C. This page covers what the material changes about the bearing, the limits it brings with it, and the sizes supplied.
Why GCr15 Bearing Steel for UC300 Series Insert Bearings
The default material for the rings and rolling elements of virtually every standard rolling bearing. In a uc300 series insert 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 |
Service Limits
The limit that catches people is dimensional stability, not hardness: a standard bearing is heat stabilized for use to about +120 °C, and running it hotter lets the rings grow and lose their fit. Above that a stabilized ring — S1, S2 and upward — is ordered specifically, and it comes with a small reduction in hardness and therefore in rating. The steel also has no corrosion resistance of its own: the preservative it ships with is not a coating, and a bearing stored in a damp store rusts on its raceways before it is ever fitted.
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.
Sizes of UC300 Series Insert Bearings Available in GCr15 Bearing Steel
| Designation | Bore d (mm) | Outer diameter D (mm) | Width B (mm) |
|---|---|---|---|
| UC305 | 25 | 62 | 38.1 |
| UC306 | 30 | 72 | 42.9 |
| UC307 | 35 | 80 | 48.4 |
| UC308 | 40 | 90 | 52.4 |
| UC309 | 45 | 100 | 55.6 |
| UC310 | 50 | 110 | 65.1 |
| UC311 | 55 | 120 | 65.1 |
| UC312 | 60 | 130 | 77.8 |
| UC313 | 65 | 140 | 77.8 |
| UC314 | 70 | 150 | 82.6 |
| UC315 | 75 | 160 | 82.6 |
