The difference in wood cutting and metal cutting bandsaws is the speed of the blade, with a wood saw running at least 20 times faster than for cutting steel. Typically, a wood saw will run 2000 FPM (feet per minute), while for steel you want about 100-150 FPM. If you try to cut steel in a wood saw, you'll destroy the blade instantly. There are some saws around that have a high/low gearbox, but you'll pay dearly for one of those. Your best bet is to have one of each if you anticipate a lot of metal cutting. You can get a very cheap metal saw for about $150-200 at Harbor Freight. I took a wood saw and converted it by putting a double reduction pulley system on it, but that's a lot of trouble. Also, most metal saws have roller bearings to guide the blade; wood saws usually just friction blocks. You CAN cut wood on a metal saw, but it's very slow.

I have a craftsman 12" bought in 1978. I use it mostly for wood but occasionally I cut brass or aluminum or copper on it. It only has one speed. I use a very fine 1/8 scroll saw blade, and first cut partway into a piece of plywood which I leave in place to act as a zero clearance support so the metal doesn't bend. You have to work slowly but it works great for that once in a while metal job. It definitely Would NOT work on steel because of the blade speed.