I have approximately 4367 old drill bits in a box. The points are too dull to cut through metal and yet I just can't bring myself to throw them out unless they actually snap. So after moving the box for the 842nd time this year, I decided to see if I could turn some into a knifes. The steel is tough, as you would expect from a drill bit, and it turned out it worked well when heated and toughened up when I treated it. These are made from some of the larger bits.
The steel that drill bits are made of is high carbon and extremely tough. I don't sharpen the edges because...I don't actually know why not, but they can be sharpened and they will hold an edge. I mostly just see these as butter or cheese knives, but if they were to be sharpened they could cut through armor. Modern drill bits are made of extremely tough steel. It holds an edge because of that toughness. The trade-off is that they are brittle. You can cut through anything but if you use them to pry or as a lever, they will snap. Tough steel won't bend much before it breaks.
Knife size ~ 7” long x 7/16" bit w/ 3” blade
Knife size ~ 6 1/4” long x 3/8" bit w/ 2 1/2” blade
I think those are the bit sizes. I don't have my index near my computer so I used a ruler. I'm close.