These are the materials that carry load. Chrome steel does it for almost every bearing sold; M50 does it when the temperature passes 250 °C; bronze does it when the bearing has to conform to a shaft instead of the other way round.
| Hardest of the three | 100Cr6 / 52100 at 59–65 HRC |
|---|---|
| Highest temperature | M50 at 315 °C continuous |
| Best conformability | Cast bronze — embeds debris instead of denting |
| Cost anchor | 52100 = 1.0× · bronze ≈ 2× · M50 ≈ 6–10× |
Steel bearings fail in fatigue: a subsurface crack starts at an inclusion, propagates to the raceway and spalls. Cleanliness of the steel — oxygen content, inclusion size — matters as much as hardness, which is why bearing-grade steel is specified to a cleanliness standard and not just a chemistry. The three materials here trade fatigue life against temperature, cost and conformability.
Bronze is not a fatigue material in the same sense. It is a bearing material for sliding contact: it embeds dirt, conforms to misalignment, runs against an unhardened shaft and tolerates marginal lubrication. Comparing it to 52100 on dynamic load rating is a category error; compare it to a steel bushing or a needle bearing.
The default bearing steel: 59–65 HRC, highest fatigue limit, 120 °C standard.
Read →4% Mo, 4% Cr — the aero-engine answer to 315 °C and very high dn.
Read →Conformable, embeddable, seawater-tolerant sliding material for bushings.
Read →Only if the shaft is hard enough and aligned well enough. Bronze tolerates a soft shaft, edge loading and debris; a ball bearing needs a hardened, ground and aligned mating surface, and it needs a lubricant film. The swap usually requires reworking the shaft, not just the bearing.
It is a vacuum-melted, high-molybdenum tool steel produced in small heats, hardened under tight control and usually supplied with full traceability for aerospace. The material cost is high, the lot sizes are small and the grinding is slower.
No. Steel cleanliness, heat-treatment quality, residual stress and surface finish all move fatigue life by factors, not percentages. That is why a certificate quoting 60 HRC tells you very little on its own.
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