never done a drill bit before, but if i was going to try. i would take 1of them and normalize it then heat to different stages and try and when i got to a suitable hardness versus brittleness. i would normalize the rest, sharpen then temper to the same color. probably a blue on the cutting end gradually getting softer up the shank. you'll probably have some scale to contend with but that may be easier than having to reshape a hardened cutting edge. warpage could be a problem but if just for normal holes and nothing that has to be exact, it might not be to bad.