I use oil hardening drill rod for just about all small parts. Starting out with a round piece to make something like an extractor may not make sense, but all my round stock is drill rod so it eliminates the guesswork when I'm looking through my metal bins. Not sure how an extractor should be hardened though, I don't have a furnace so I usually just heat with a torch, quench in oil and reheat until I get the temper color I want. You may want to go to straw yellow on an extractor, it needs to have more wear resistance than flexibility.
In other words, my approach is not very scientific. I just fly by the seat of my pants but it has worked well so far.
