TS · tool steel
Bearing Steel 52100 (100Cr6)
The through-hardening bearing steel: machines acceptably in the spheroidise-annealed condition, then hardens to 60–66 HRC for rolling contact service.
Quoting this material
- Typical lead time
- 14–22 working days
- Condition
- Spheroidise annealed for machining; through hardened and tempered for service
- Achievable finish
- Ra 0.2 µm after grinding typical · Ra 0.05 µm (superfinished) best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
The through-hardening bearing steel: machines acceptably in the spheroidise-annealed condition, then hardens to 60–66 HRC for rolling contact service.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Hardness (working) | 60–66 | HRC |
| Rolling contact fatigue | Highest of the common steels | - |
| Wear resistance | Very high | - |
| Dimensional stability | Needs grinding after hardening | - |
| Thermal conductivity | 46.6 | W/m·K |
| Modulus of elasticity | 210 | GPa |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Spheroidise annealed for machining; through hardened and tempered for service
Heat treatment
Austenitise around 830–850 °C, quench in oil, temper at 150–200 °C for maximum hardness. Dimensional movement is significant and predictable, which is why bearing races are ground after hardening, never before.
Achievable surface finish
Ra 0.2 µm after grinding
Ra 0.05 µm (superfinished)
Rolling-contact surfaces are superfinished: bearing life is a function of surface finish and the residual stress the grinding leaves behind.
Tooling and cutting parameters
Cutting speed
- 120–200 m/min annealed (carbide) · 40–70 m/min at 62 HRC (CBN)
Feed
- 0.08–0.20 mm/rev turning · 0.05–0.12 mm/tooth milling
Tooling
- Coated carbide annealed; CBN for hardened races
Coolant
- Flood; heat control at the edge decides the surface integrity
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Bearing rings and rolling elements
- Spindle shafts and journals
- Rolling contact wear surfaces
- Cam followers and rollers
- High-cycle fatigue components
DFM notes for this grade
- It is a rolling-contact material: using it as a general wear plate wastes the property you are paying for and makes the grinding harder
- Never finish a race before hardening: the movement is predictable but it is larger than the tolerance band of a bearing seat
- The grinding process matters as much as the material - a burn mark on a bearing race is a fatigue initiation site, so the wheel and the coolant have to be right
Questions buyers ask
- What makes bearing steel different from a tool steel at the same hardness?
- Cleanliness. 52100 is made to tight limits on oxide inclusions because a rolling contact fails at an inclusion, not at the surface. Tool steels are not made to that cleanliness class, so the fatigue life of a tool-steel race would be unpredictable.
- Can you machine a 52100 part to a bearing tolerance?
- The machining produces the pre-hardening geometry; the final tolerance comes from grinding after hardening. A bored-and-honed 52100 housing can hold ±0.005 mm, but if it is later hardened, the dimension will move and the honing has to be repeated.
Grades we would quote instead
D3
4/10More carbon and more carbide than D2, so more wear resistance and less toughness - and slightly harder to machine and grind in the annealed state.
D2
4/10Annealed it machines reasonably but it is abrasive on the tool because of the chromium carbides.
17-4 PH
4/10In the annealed condition it machines like a tough 304; in H900 it is hard enough that finishing has to be done by grinding or hard turning.