Why Do Bearing Races Fail?
A bearing race fails by spalling: material flaking from the raceway under rolling contact. The crack that causes it almost always starts below the surface, at an inclusion.
Bearing races fail by spalling — material flaking from the raceway under rolling contact fatigue. The initiating crack almost always starts at a subsurface non-metallic inclusion where peak shear stress occurs, which is why steel cleanliness governs bearing life more than hardness.
- Primary mode
- Subsurface-initiated spalling
- Root cause
- Non-metallic inclusions
- Material
- EN31 / 100Cr6, 60–64 HRC
- Fit control
- Bore tolerance ±0.02 mm
- Ring type
- Seamless rolled, no weld
Why Do Bearing Races Fail? at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Spalling initiates below the raceway surface
- EN31 hardens to 60–64 HRC
- Cleanliness matters more than hardness for life
- Seamless rolled rings avoid weld failure sites
Rolling Contact Fatigue and Inclusions
Under Hertzian contact, maximum shear stress occurs a fraction of a millimetre below the surface. A non-metallic inclusion sitting there concentrates that stress and initiates a crack, which propagates to the surface and spalls. Steel cleanliness therefore governs bearing life more than hardness does.
- Peak shear is subsurface, not at surface
- Inclusions there initiate spalling
- Cleanliness governs life
- EN31 bought against inclusion limits
Fits, Contamination and Lubrication
An over-tight interference fit raises hoop stress and can crack a race. Too loose and it creeps and frets. Contamination dents the raceway, each dent becoming a stress raiser. Inadequate lubrication allows metal-to-metal contact and rapid surface distress.
People also ask
Why is bearing steel bought against inclusion limits?
Because rolling contact fatigue initiates at subsurface inclusions. Strict cleanliness limits directly determine how long the bearing survives, independent of hardness.
Can an incorrect fit crack a bearing race?
Yes. Excessive interference raises hoop stress in the ring and can crack it; too loose a fit allows creep and fretting damage.
What hardness should a bearing race be?
Typically 60–64 HRC after hardening and low tempering, in EN31 or 100Cr6 bearing steel.
Topics covered on this page
- bearing race
- spalling
- rolling contact fatigue
- inclusion rating
- EN31
- 100Cr6
- Hertzian stress
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
What causes bearing race spalling?
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Rolling contact fatigue initiating at a subsurface non-metallic inclusion, where peak shear stress occurs beneath the raceway surface.
Why does steel cleanliness matter so much for bearings?
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Because the crack that ends a bearing's life starts at an inclusion. Fewer and smaller inclusions directly extend fatigue life.
Should bearing races be seamless rolled?
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Yes. A welded ring has a heat-affected zone and interrupted grain under rotating hoop stress, which becomes the failure site.