Chemical Changes in Steel Surfaces During Extreme Pressure Lubrication

Abstract

Films and wear fragments from unfailed test cups from SAE extreme pressure runs with sulfurized mineral oil and films from unfailed hypoid gear teeth run in commercial gear oils were analyzed by six methods. The major compound was Fe₃O₄ or a similar spinel. Minor constituents were FeS, FeO, and an “iron carbide.” Emission spectrographic analysis showed silicon in much greater concentrations than in the base metal. The beneficial effects of silicon enrichment are discussed and the mechanisms that might cause it to concentrate in the surface, Bench test data are given demonstrating how poly (methylphenylsiloxane) can increase the load-carrying capacity and reduce the wear of gear oils.