M50 is what you fit when the housing sits at 200 °C or more and a standard bearing has already failed twice. Electric Motors & Drives duty is continuous speed, long grease life and shaft voltages from PWM drives; the material is what decides whether the bearing survives it.
| Industry duty | 1,500–6,000 rpm continuous, up to 20,000 rpm on servo drives |
|---|---|
| Typical media | cooling air, dust, occasional washdown |
| Housing temperature | −20 to +120 °C |
| Material and grade | M50 high-speed tool steel |
| Hardness | 60–65 HRC |
| Temperature ceiling | 315 °C |
| Corrosion / chemical | none — needs protection like 52100 |
| Relative cost | ≈6× of a standard 52100 bearing |
Steel loses hardness on a time-and-temperature curve, and a standard 52100 ring tempered for 150 °C is already softening at 200 °C. The secondary-hardening alloys — M50, M50 NiL, 440C to a lesser degree — keep their hardness because the tempering reaction that softens them happens above the service temperature. That is what preserves clearance and preload in a hot housing, and it is the only reason to pay for the grade.
| Position | Bearing type | Material / finish | Why it works there |
|---|---|---|---|
| Drive end, hot housing | Deep groove ball | M50, C4, 2Z, high-temperature grease | Hardness retained at 250 °C; C4 leaves room for ring growth. |
| Kiln conveyor roller | Deep groove ball | M50, or stabilised 52100 S2 | At 180–220 °C stabilised 52100 is the cheaper answer; M50 starts where that runs out. |
| Exhaust fan shaft | Self-aligning ball | M50 on request | Misalignment plus heat; the self-aligning seat absorbs frame distortion. |
| Material | Fit here | Choose it when |
|---|---|---|
| M50 | Best fit | Housing above 200 °C continuously, where stabilised 52100 has already failed. |
| 100Cr6 / 52100 | Workable alternative | Below 200 °C with S1/S2 stabilising — a sixth of the price for the same result. |
| Si3N4 | Workable alternative | Above 300 °C, or where grease has been abandoned and the bearing runs dry. |
Only above 200 °C. Below that, a stabilised 52100 gives the same dimensional stability. The premium buys hot hardness, not general quality.
At 300 °C, no grease survives for long. M50 with a solid lubricant or a ceramic hybrid is the usual combination, and the design should assume relubrication is impossible.
Thermal growth of the ring plus loss of temper. At 250 °C a 100 mm ring grows about 0.25 mm more than the housing, which is why C4 and M50 go together.
Hardness, temperature, corrosion and equivalents for M50 tool steel.
Read →Typical duty, recommended types and suffixes for electric motors.
Read →Standard duty — shaft ends and bearing housings in induction motors from 0.75 to 200 kW.
Read →Washdown & food plant — motors on washdown duty in food, beverage and pharmaceutical plant.
Read →Send the position, bore size, quantity and the medium it sees. We reply with the material certificate, clearance class, lubricant and price within 30 minutes on working days.