M50 keeps 60 HRC at 315 °C, which is the only reason to pay six times the price of a stabilised chrome steel bearing. Steel & Metallurgy duty is very high load, heat and cooling water washing the grease out; the material is what decides whether the bearing survives it.
| Industry duty | rolling force with heavy axial component, 60–200 °C at the roll neck |
|---|---|
| Typical media | mill scale, cooling water, grease |
| Housing temperature | 60 to +200 °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 |
Heat treatment is a one-way street: a ring tempered for 150 °C loses hardness progressively above it, and the growth that comes with that loss closes the internal clearance. Secondary-hardening steels such as M50 are tempered above their service temperature, so the structure is stable at 250–300 °C. In a furnace-adjacent position that is the difference between a planned campaign and a monthly bearing change.
| Position | Bearing type | Material / finish | Why it works there |
|---|---|---|---|
| Furnace roller neck | Self-aligning roller | M50, C4, high-temperature grease or oil | Housing at 250 °C; hardness and clearance retained. |
| Hot strip run-out | Cylindrical roller | M50, four-row on request | Heat plus load; standard steel softens and loses clearance. |
| Furnace fan shaft | Deep groove ball | M50, C4, 2Z | Hot air at 250 °C with light load. |
| Material | Fit here | Choose it when |
|---|---|---|
| M50 | Best fit | 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. |
| Si3N4 | Workable alternative | Where grease has been abandoned and the bearing runs dry at 400 °C. |
When the housing stays above 200 °C. Below that, stabilised 52100 has the same dimensional stability and the premium buys nothing.
Thermal growth plus loss of temper. At 250 °C a 200 mm ring grows about 0.5 mm more than the housing, and a softened ring also yields under the fit.
No conventional grease survives that. Above 250 °C the design has to use oil-air, a solid lubricant or a ceramic hybrid.
Hardness, temperature, corrosion and equivalents for M50 tool steel.
Read →Typical duty, recommended types and suffixes for steel mills.
Read →Roll neck & mill drives — roll neck, mill drive and run-out table positions.
Read →Mill auxiliaries — run-out table bushes, guide rolls and slow auxiliary shafts.
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.