Material specification page for bk series closed end drawn cup needle roller bearings in Case-Hardened 20CrMnTi. Covers the grade designation (20CrMnTi (GB/T 3077), of the same class as 20MnCr5 and SAE 8620 — carburized to a hard case over a tough, unhardened core), what the material does inside the bearing, its temperature and environmental limits, the alternatives worth considering, and the sizes available to ISO 3245 / DIN 618-1 / GB/T 290.
Why Case-Hardened 20CrMnTi for BK Series Closed End Drawn Cup Needle Roller Bearings
Chosen for shock loading and for heavy ring sections, where a tough core resists the cracking a fully through-hardened section would not survive. 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.
Carburizing puts the hardness where the rolling contact is and leaves the core tough, so the ring can absorb shock and heavy section stresses that would crack a through-hardened ring. It is the usual choice for large roller bearing rings and for anything that gets hit rather than merely loaded.
Material Properties
| Grade designation | 20CrMnTi (GB/T 3077), of the same class as 20MnCr5 and SAE 8620 — carburized to a hard case over a tough, unhardened core |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | Similar to through-hardened rings — about +120 °C without special stabilization |
| Corrosion characteristic | None of its own; protected in service exactly as through-hardened bearing steel is |
Alternatives and When to Switch
Through-hardened GCr15 is the alternative and the default: it is used wherever the section is modest and the load is steady, which is most of the catalog. Case-hardened rings earn their place under shock and in large sections.
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 Case-Hardened 20CrMnTi
| 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 |
