I've made small skews, scrapers, point tools, and 'skewchiegouges' (a tool that is round like a gouge, but that doesn't have a flute and cuts more like a skew) from old screwdrivers, hex-shank interchangeable screwdriver bits, allen wrenches, and drill bits.
These steels start out fairly hard. It would be nice to treat them for additional hardness, but the main objective would be to help them hold an edge longer. My experience is that even without additional hardening, they can be sharpened and are great for fine work that doesn't involve hogging away large amounts of waste.
One thing to be careful about is the length of the shank - if the shank is too long, you will have unacceptable vibration and chatter. But the shank has to be long enough to support the overhang that you must have when using the tool. One solution to this dilemma is to make the main shank of the tool from mild steel bar, and then embed the cutting tool in the end of that bar with only a very short extension (perhaps 1/2"). You can mount a mild steel bar in a wood lathe (in a scroll chuck) and with it spinning, use an ordinary file to smooth and taper the end. It's slow work - just be patient and it will happen. And you can drill a receiver hole in the end of the bar on the lathe just as you would drill a pen blank. Once you have the hole, you can glue the cutter into the hole using epoxy. If you ever need to remove the cutter, just heat the glue joint to soften the epoxy.
