Joe: You will need to fully harden the steel that you wish to make into a spring. The amount of hardness verses toughness left in the steel is a function of the tempering process the hotter the temp. of the tempering process the less hardness and the more toughness will be left in the steel.
Here is what my blacksmithing book gives me
oxide color temp. F tools
yellow 420 Engravers
Scrapers
razers
Pale straw 430
440 Stone drills
reamers
Straw or orange 450 Saws for metal
Deep straw 470 Scribes,
punches
brown 480
490 dies
500 knifes, plane iron
510 Chisels, drill
bronze 520
light purple 530 hammers
540 axes, center punch
purple 550 cold chisels
blue 570 screwdrivers
dark blue 590 springs, wood saws
600 large saws
610 large springs
Greenish blue 630
I realize this is not an axact answer, but it is a good starting place. If you are buying your steel from a supplier they should be able to give you the heat treating properties of the steel, most are glad to do so. In addition if you are making a small spring it can be tempered by placing the metal in a small can cover the part with a layer of motor oil and heat it with a propane tourch until the oil begins to burn on its own. Waite until the oil is all comsumed the part will be tempered to the proper hardness. This is an old method that I have read about but never tryed. The idea here is that the oil will only reach so high a temp. even while burning. Hope some of this helps, and good luck.
G2
