Here is a flat head screw driver I made from a section of lawn mower blade.
Lawn mower blade doesn't really harden very well, but it does take on a sort of toughness to it.
Almost as if it's about the same toughness as a piece of spring steel hardened and tempered at a blue heat or 572 degrees Fahrenheit (300 degrees Centigrade).
I quenched it in a can of brine water and that did a good job.

The handle is made from a scrap of sledge hammer handle and the ferrule is the end of a CO2 cartridge.

As you can see by the picture, the screw driver blade fits neatly into the screw.