It might be helpful to understand what is going on down there at the atomic level when you are annealing, hardening, and tempering.
Steel is a cubic crystal. Imagine a bunch of dice, all with one spot on each face. Each spot is one carbon atom and the corners are iron atoms. When the carbon is out on the face the steel is soft. If you heat the steel up to its critical temperature (about 1450F - it varies with the steel) the carbon atoms sink into the center of the cube. If you cool the steel quickly then the carbon stays in the center, the crystals lock together, and the steel is hard, but brittle. If you then heat the steel part way to the critical temperature some of the carbon comes back to the surface and the steel gets more flexible.
The more carbon, up to about 1.3%, the more potential for hardness (and brittleness). You can quench mild steel (0.10%) however you want and it won't do any good.
For springs, you want about 0.60-0.75% carbon. My recommendation: spend the money on the right steel - steel with detailed specifications attached. Save yourself time and frustration. Mr. Jakowski, the stuff you are getting from McM is perfect - plain steel with 75 points of carbon.
A useful tool is one of those pick-up magnets on a stick, because steel becomes non-magnetic at its critical temperature. Forget about color, just heat it just till the magnet doesn't stick.
Forge the spring at no more than a yellow heat to preserve the carbon - it tends to oxidize out, especially in small parts, at high temperatures. When it is finished give it one more heat to critical temperature and stick it deep in a pot of wood ashes. Let it cool for a couple of hours. Heat it to critical again and put it in the ashes again.
Now that it is dead soft, grind (drill if necessary) and polish it to its final finish.
Wet it and dump some blue chalk-line chalk on it. Rub it into a smooth layer all over and let it dry. This will protect it somewhat from oxidizing when you heat it again. The color of the chalk doesn't matter - I just like blue.
Heat it carefully in a low oxygen fire (thick coal bed or slightly long torch flame) to critical and quench it in its designated quench liquid. Some steels like oil, others water. (Others air, but you don't want that stuff) Buy the steel from McMasters or wherever and it should say. I use veg oil for oil hardening steel because it smells better than petro oil. Mmmm - fries with that?
Carefully clean the spring and brighten it to white again. Heat it with a propane torch till it is a uniform deep blue and let it cool. If you want to be really scientific, look up the tempering temperatures from the supplier and get a tempering crayon to match. Tempering crayons are just what you might think - they melt at specified temperatures in the 400F to 1500F range. You put a mark on the piece and heat it the the mark melts.
Well, there's a novel length post.
Hope that helps. I learned that at my master-smith's side about 30 years ago.
