shape and all heat to non magnetic and let cool in still air 2-3 times and then Bring up to non magnetic again and quench in Oil. then polish up to shiny one side of it (from one end to the other) of it and heat the middle till the hammer hitting end gets purple and the punch end get to a dark straw but keep it up a bit more so that a blue/purple colour goes down to 1-1,5cm from the tip that way it is only the end that "does the business" that is really hard and rest of it is strong.
and remember to cool very often while driving a hole in hot iron, and the tool will last long.
just my 2 cents.
EDIT: ohh forgot I use spring steel for mine, like from old leaf springs and such
Cheers
DC