Study on the tribological properties of plasma nitrided bearing steel under lubrication with borate ester additive

The nitrided layer on 52100 steel was prepared by plasma nitriding treatment. The tribological behaviors were examined under lubrication with borate ester containing nitrogen (B-N). The nitrided steel exhibited a lower friction coefficient and smaller wear scar diameter compared with the untreated steel. When 1.25 wt% B-N was used, the friction coefficient and wear scar diameter of nitrided steel were reduced by 34% and 45%, respectively. The main mechanism of this effect was attributed to the fact that the B-N additive can produce a tribofilm containing higher content of BN on the nitrided surface.