Just to get some comments flowing, here's a comemnt Howard Clark made about this subject yesterday at the Guild of Metalsmiths Conference in Hastings, MN:
"Since about the 1950's GM leaf springs have been made from 5160."
Then he goes on to say that "GM COIL springs of that same era are made from 9260". That part was a total surprise to me. 9260 has hardly any Chromium and about 2% Silicon. I asked him if that applied to torsion bars but he said he didn't know.
Howard appears to think of 5160 and 9260 as fairly similar materials (from a usage standpoint) though.
He calls the 5160 "fool proof" for reasons that are clear to many of you. It hardens up easily, whereas the 9260 has to be cooled somewhat faster and, I think, more carefully to get full hardness.
I ain't a knife maker, so I'm not trying to come on as an expert, it's just that I had assumed that "a spring is a spring" (GM-wise).
The only time I use junkyard steel for tools is when I'm not in my own shop. There, I stick to Atlantic 33, S1 and S7 for hot work, 4140 for die work, and W1 for cold working tools just because I got a LOT of it cheap.
Pete Stanaitis