Abstract: The surface hardening of overbased calcium sulfonate complex grease containing different concentrations of anti-oxidant L57 and L135 was studied. The tribology of the grease containing different additives was investigated using MFT-R 4000 reciprocating friction tester after 40 days storage. The worn surface was observed by scanning electron microscope (SEM) and energy spectrum analysis. The results show that antioxidants can postpone the surface hardening of the grease tested and the complex greases containing 2% L57 and 2% L135 have a better tribology performance.

Key words: anti-oxidant, overbased calcium sulfonate complex grease, friction, wear, cone penetration