Originally Posted by RSandy

basically the peening removes tensile stresses and replaces with compressive stresses, which reduces fatigue and increases product life. also in cast parts, most imperfections and hairline cracks originate at the surface, so they are either removed by the peening, or the cracks themselves arent as problematic when in compression

in a nut shell, twat it with lots of shot and make it look all dimpled lol