It involves stretching the weld bead over the surface to thin it out, and this action reduces the stress induced by the metal contraction as it cools. ... Peening prevents the weld joints surface from developing cracks that lead to fatigue-resistance failure and stress corrosion.

What is the benefit of peening a surface?

Shot Peening, also known as shot blasting, causes the material in the surface zone to yield by literally shaking the metal grains into a more relaxed state. As a result, the surface layer counteracts tensile stress and effectively prevents cracking.

What does peen a weld mean?

A step in die welding that isn't discussed very often, according to Wilcox, is peening. Immediately after weld metal is deposited, and while it is cooling it is peened with a tool similar to a mini jackhammer. The peening process counteracts the tendency of the weld metal to shrink and tear away from the die metal.