Study of the Lubrication Mechanism of Thin Film Lubricated Concentrated Steel Contacts. The Influence of Pre-Treatment of the Steel on the Load Carrying Capacity

The effect of the thermochemical surface treatments carburizing, ion-nitriding and liquid-nitriding on the load carrying capacity at high speed (4 m/s) of sliding crossed cylinders of steel, thin film lubricated with a marine diesel engine oil of 60 C, is described for three values of running-in distance, namely 0 m, 30 m and 300 m; running-in being performed at a speed of 0.1 m/s. It is shown that when using untreated surfaces of ball bearing steel 100 Cr 61), carburized surfaces or ion-nitrided surfaces, loading in excess of a critical load value FNc causes a transition from partial elastohydrodynamic lubrication to unlubricated contact (scuffing regime). When using liquid-nitrided surfaces, loading in excess of FNc leads to a transition from partial EHD lubrication of boundary lubrication. This shows that liquid-nitriding considerably increases the upper limit of the temperature range in which boundary lubrication is possible.