GCr15 Bearing Steel BK Series Closed End Drawn Cup Needle Roller Bearings: The default material for the rings and rolling elements of virtually every standard rolling bearing. The material decides the corrosion behavior — none of its own — the ground surfaces are bare hardened steel and depend on the lubricant, the seals and the preservative for protection and the temperature the part will stand (to about +120 °C as normally heat stabilized; stabilized rings (S1, S2 and above) extend the limit in steps to around +250 °C), and it is the reason the alternatives below exist. Properties, limits and the full size table follow.
Why GCr15 Bearing Steel for BK Series Closed End Drawn Cup Needle Roller Bearings
The default material for the rings and rolling elements of virtually every standard rolling bearing. In a bk series closed end drawn cup needle roller 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 BK Series Closed End Drawn Cup Needle Roller Bearings Available in GCr15 Bearing Steel
| Designation | Bore Fw (mm) | Outer diameter D (mm) | Width C (mm) |
|---|---|---|---|
| BK0808 | 8 | 12 | 8 |
| BK0810 | 8 | 12 | 10 |
| BK1010 | 10 | 14 | 10 |
| BK1012 | 10 | 14 | 12 |
| BK1210 | 12 | 16 | 10 |
| BK1212 | 12 | 16 | 12 |
| BK1312 | 13 | 19 | 12 |
| BK1412 | 14 | 20 | 12 |
| BK1512 | 15 | 21 | 12 |
| BK1516 | 15 | 21 | 16 |
| BK1612 | 16 | 22 | 12 |
| BK1616 | 16 | 22 | 16 |
| BK1812 | 18 | 24 | 12 |
| BK1816 | 18 | 24 | 16 |
| BK2012 | 20 | 26 | 12 |
| BK2016 | 20 | 26 | 16 |
| BK2020 | 20 | 26 | 20 |
| BK2212 | 22 | 28 | 12 |
| BK2512 | 25 | 32 | 12 |
| BK2516 | 25 | 32 | 16 |
| BK2520 | 25 | 32 | 20 |
| BK2820 | 28 | 35 | 20 |
| BK3012 | 30 | 37 | 12 |
| BK3016 | 30 | 37 | 16 |
| BK3020 | 30 | 37 | 20 |
| BK3520 | 35 | 42 | 20 |
| BK4020 | 40 | 47 | 20 |
