Editorial

Abstract

It is extraordinary that a steel bearing can survive stress pulses of 2 GPa some half a million times a minute, over the service life of an aero engine. Or that it can be expected to reliably support the stochastic loads created by the buffeting of sails on giant offshore windmills designed to rescue the world from carbon dioxide catastrophes and wars driven by the thirst for oil. Bearing steels are the unsung heros of most of the arduous technologies that improve the quality of ordinary life; for the person pulling the rickshaw in Kolkata to the farmers harvesting the vast bread baskets of the prairies.And yet, the vast majority of bearing steels have their origins in the dim and distant history of tool steels. Tool steels must obviously be hard but do not necessarily have to be tough. A bearing consists essentially of parallel rings with some form of rolling element (balls, cylinders) accommodating the relative motion of the inner and outer rings. It therefore needs to sustain periodic contact stresses as the rolling element traverses the substrates. These loads are mostly a combination of torsion and compression, so it is not surprising that Stribeck in 1901 considered the 1C-1?5Cr tool steel for bearing applications, and that this steel was adopted by Fichtel and Sachs in 1905 for manufacture. Naturally, as technology became ever more demanding, so did the adaptation of the original tool steels, with dramatic improvements in cleanliness which led to corresponding enhancements in rolling contact fatigue life.Developments in the aircraft industries led the demand for higher operating temperatures, and hence the adoption of secondary hardening tool steels for aero engine bearings, followed by the case hardening versions to enhance core toughness. We are fortunate to have been able to persuade Zaretsky, one of the pioneers of the subject, to contribute a historical perspective to this special issue. 1