I just finished shaping the tips of a mongrel group of turnscrews I cobbled together over the past year, so I expect they are made of different steels.
It seems to me that it couldn't hurt to heat treat the tips, which I think I should be able to accomplish with a propane torch without removing the handles.
I was thinking to heat to red, quench in oil, and temper to indigo/blue.
Should that work for all the varieties of steel ordinarily encountered with vintage turnscrews?