Influence of Steel Composition on Additive Performance

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Abstract
Coatings formed by lubricants on rubbing surfaces are believed to control the friction, wear, and fatigue of rolling contact bearings, gears, cams and tappets, and other heavily loaded components. To investigate the influence of steel composition on the formation of these surface coatings, friction, fatigue, and static immersion studies were conducted with two case-hardened steels (1018 and 4118) and five through-hardened materials (51100, 52100, M-50, 440-C, and Stellite #3). More surface coating formed on the low alloy steels than on the high alloy steels, with the composition of the oxide layer apparently being the controlling factor. The magnitude of the steel effect depended on the additive and the oxygen available. Elemental analyses of the surface coatings obtained with representative additives indicated that all contained significant organic fractions. Decomposition of the additive in the bulk oil was a necessary prerequisite for surface coating formation. Additive decomposition was generally promoted by oxygen, but was independent of the steel composition.