GCr15 Bearing Steel 6800 Series Thin Section Ball Bearings

In a 6800 series thin section ball bearings, GCr15 Bearing Steel is the steel of the rings and, in most designs, of the rolling elements. The grade is GCr15 (GB/T 18254) = 100Cr6 (1.3505) = SAE 52100, through-hardened to 58–64 HRC; it is magnetic, and its usable service range is to about +120 °C as normally heat stabilized; stabilized rings (S1, S2 and above) extend the limit in steps to around +250 °C. This page covers what the material changes about the bearing, the limits it brings with it, and the sizes supplied.

Why GCr15 Bearing Steel for 6800 Series Thin Section Ball Bearings

The default material for the rings and rolling elements of virtually every standard rolling bearing. In a 6800 series thin section ball bearings it is the steel of the rings and, in most designs, of the rolling elements.

Through-hardened high-carbon chromium steel is what a raceway is: hard enough to resist the rolling contact stress, clean enough after modern vacuum degassing that the inclusions which start fatigue cracks are rare, and dimensionally stable after tempering so the ground bore stays the size it was ground to.

Material Properties

Service Limits

The limit that catches people is dimensional stability, not hardness: a standard bearing is heat stabilized for use to about +120 °C, and running it hotter lets the rings grow and lose their fit. Above that a stabilized ring — S1, S2 and upward — is ordered specifically, and it comes with a small reduction in hardness and therefore in rating. The steel also has no corrosion resistance of its own: the preservative it ships with is not a coating, and a bearing stored in a damp store rusts on its raceways before it is ever fitted.

What the Material Changes About the Bearing

The material does not change the envelope: the bore, the outside diameter, the width and the corner radius stay exactly as the boundary dimension standard fixes them, so the bearing is interchangeable with any other bearing of the same designation. What it changes is what happens inside the contact — the fatigue behavior, the tolerance of shock, and the temperature at which the ring stops being dimensionally stable.

Fitting a Steel Bearing in an Aluminum Housing

Aluminum has roughly twice the coefficient of thermal expansion of bearing steel, so a housing bore machined to a normal H7 fit at room temperature grows away from the outer ring as the machine reaches operating temperature. The outer ring then turns in its seat and wears the bore. Where the housing is aluminum and the temperature rise is more than about 30 degrees C, tighten the housing fit by one grade — J7 or K7 in place of H7 — or fit a steel sleeve into the aluminum. Check the resulting internal clearance: a tighter housing fit takes clearance out of the bearing, which is often why C3 is specified alongside it.

Sizes of 6800 Series Thin Section Ball Bearings Available in GCr15 Bearing Steel