any heat-treatable thin steel plate/strip recommendations?

Since you haven't mentioned where you are i'll start with a suggestion for a UK company

. Of your 3 requirements it may be an issue of pick any 2. I have bought spring steel before in 0.065" and above but the sheet size was minimum 13" x

72". That was from West Yorkshire steel , they do do thinner IIRC.

Try this place:

I bought several thousand feet of C1075 annealed spring steel from them, slit to my specs. No problems. They also had the best pricing I could find in the US.

Bill

AISI 4130 qualifies, depending on your definition of "cheap."

You want to cut/bend it and then heat-treat it? That's not so easy for

0.020 stock. I think thin, hard steel such as shim stock and music wire are generally hardened by cold working.

5-15 ph stainless would not be cheap unless you found it surplus. But the heat treatment is very easy.

Dan

And would be much less likely to warp in the process. 17-4 would also work, maybe 17-7 as well.