I saw this and thought of Miss V.
Some good useful info to have and be able to use.
Peening lies somewhere between the art of jewelry making and blacksmithing. You are using the hammer to redistribute the metal ever so slightly. Think of the steel as a very dense modeling clay that can be coaxed into shape by moderate repetitive force. Heavy hammer blows are unnecessary. A firm yet sensitive strike that makes a good solid sound is your goal.
Lots of valuable info HERE as well and tools for the job.