With air hardening steel used for a spring you don't want to harden it as hard as you would for most applications. Warming it up to orange will harden it enough to make a spring. Lots of room to play with squirting it with oil or water to get the strength desired. No need to wrap it up with stainless either depending on the use.
The entire surface of the spring is exposed to a barrage of tiny steel balls that hammer it smooth and compress the steel that lies just below the surface. 6 Setting. To permanently fix the desired length and pitch of the spring, it is fully compressed so that all the coils touch each other.
After spending the summer working on my L.E. American, I have finally returned to working on my 7.5" gauge 1909 streetcar. I left off on that project being stuck for leaf springs for the trucks but I have now found a source (in Canada) for 1095 "hardened and tempered" blue spring steel from 0.003" and up. Start the same way and make a few turns of an expansion spring (wire touching itself). Then wrestle the spacer (keystock) in between the last turn and rest of the still straight wire. Spin a bunch of turns with the spacer and then finish it with a few more expansion turns. FYSETC Ender 3 Printer Upgrade Bed Spare Parts, Spring Steel Sheet Heat Bed Surface 235x235mm/ 9.2x9.2 inch, Hotbed Build Plate, with Circular Magnets PEI Platform for Creality Ender 3 3.7 out of 5 stars 13
Stainless Spring Steel We stock stainless steel sheet and strip from .20 mm thickness to 3.00 mm in 301 temper rolled and 420 hardened and tempered. 301 is ideal for making small springs without the necessity for heat treatment. 420 is suitable for the manufacture of blades, cutlery etc. C1008/1010 HR Steel Sheet - (ASTM A1011, A569) Hot Rolled Steel Sheets are the most economical steel sheets available for a wide variety of applications.HR Steel Sheets are easy to weld, form and drill, and has a slight grainy surface.