Hey 340, Wiki first states that it adds compressive stress then later says relives stress. Thats the stuff that i'd like to get to the bottom to. Which one add/relieve? An old mentor of mine that was McDonnell Douglas ball bearing top dog said it added stress. I'm on same page as Transman.
There is no universal answer, it just depends on the process that the factory follows. Typically the internal stress from forging would be taken care of by tempering. Then the part is machined, heat treated and shot peened. But engineers are free to experiment with different process flows so there might be someone somewhere who decides to shot peen after forging but before machining. In that case the shot peening would relieve internal stresses.
