The Pitting and Cracking of SAE 52100 Steel in Rolling/Sliding Contact in the Presence of an Aqueous Lubricant

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Abstract
The use of aqueous lubricants is well established in applications where their fire-resistant properties are of prime importance. A major disadvantage of the use of such fluids, however, is their relatively poor performance in high-stress rolling-contact bearings where components suffer fatigue cracking and pitting at an earlier stage than with mineral oils. In this investigation, factors affecting the cracking and pitting of SAE 52100 steel in the presence of a water-glycol-based fluid have been studied using an Amsler two-disk machine. A Stribeck curve was plotted and has shown that pitting damage is dependent on the region of the curve in which the system is operated, pitting life being a minimum in mixed-elastohydrodynamic lubrication. Good correlation was found betwen pitting life and specific film thickness λ above λ = 0.05. Below this value, inverse correlation was observed. Finally, a mechanism for crack initiation, propagation, and subsequent pitting in aqueous fluids is proposed.