This is the fundamental use of shot peening. The energy transfer due to plastic deformation creates dislocations in the grain structure along with this the plastic deformation introduces compressive stress. The combination of these two effects provides a highly effective method of introducing negative stress states in the surface and subsurface of the material.
The graph to the left indicates a typical residual stress profile, with maximum compressive residual stress between 0.03 and 0.15 mm from the shot peened surface. The resultant gross residual compressive stress is a result of many factors, partly the initial state of the material, shot size, shot velocity and coverage.