Tribological properties of nitrided steels lubricated with fully formulated oils in boundary lubrication condition

Abstract

Nitriding is one of the most popular heat treatments widely used in hydraulic sliding parts of automotive or construction machinery components. Since the nitrided steels shows great wear resistance due to its high hardness, it is widely applied to various sliding parts in the hydraulic system of construction machinery. During operation, these parts are usually lubricated with fully formulated oils, which include various additives such as dialkyldithiophosphate (ZnDTP), dispersant, detergent, etc. In this study, the tribological features of two kinds of nitrided surfaces lubricated with fully formulated oil and sample oils were evaluated by changing the combination of additive element formulations, and the effect of additive formulation on tribofilm formation and frictional property were investigated in detail. As a result, it was revealed that there is a large interaction between the nitrided surfaces and additives, the coexistence of ZnDTP and detergent affects the phosphorous-derived tribofilm formation on nitrided surface as well as their frictional properties. In particular, the low frictional characteristics of nitrided compound layer was characterized by the smoothed surface and low tribofilm formation on the track.