There is great variabality in steel sheet stocks. Unfortunately, most of the commonly found sheet material available
at a local hardware store is not likely to be the best material for picks.
Most "good" steels for picks will have a moderately-high to high carbon percentage in the alloy, along with
smaller amounts of other elements, such as molybendum, manganese etc.
It's this alloy (mixture) that plays a big role in the steels performance and hardening/heat treating characteristics.
If your really interested in steel stocks and cutting and fabricating tools and equipment check with
www.mcmaster.com-- the carry industrial materials, and equipment.