Where surfaces are load carrying and lubricated a super smooth surface is not always the best for reducing contact friction. With a smooth surface the lubricant is forced away from the mating surfaces resulting in a metal to metal contact and hence high contact stress.
The effect of Shot Peening produces a micro dimpled surface, this is as a result of plastic deformation during the shot peening process. This micro surface acts a retainer for lubricant which is slowly released during contact stress, this slow release of lubricant acts as an effective surface film which significantly reduces contact stress.
Babić, S. Mitrović, D. Adamović, D. Džunić, F. Živić Faculty of Mechanical Engineering, Sestre Janjic 6, Kragujevac, Serbia, 2011
As can be seen by the work done by (M. Babić, S. Mitrović, D. Adamović, D. Džunić, F. Živić Faculty of Mechanical Engineering, Sestre Janjic 6, Kragujevac, Serbia, 2011) shot peening significantly reduces the wear rate of allow steel where lubrication is present compared to a ground surface.
The Effect of Shot Peening on Tribological Behaviour of Alloyed Steels
As can be seen from the graph the frictional properties of alloy steels can be significantly reduced by the use of shot peening.