Hi,
If you use the search function I am sure many posts about this will come up. It has been asked many times on this forum. I make many main springs, frizzen springs, and sear springs from scratch. I almost always use 1075 steel which makes fine springs and is very forgiving. I would never use scrap because not knowing the alloy means I'll be unsure of the best hardening and tempering regime. Using a good alloy like 1075 or even 1095 steel is the first step in a good spring. Next is the shaping. It must be shaped, which includes tapering the leaves to get the desired performance. You cannot adjust the performance of a spring much by different hardening and tempering regimes. The most important factor is how the leaves are shaped. The finished and shaped spring must first be hardened. For 1075 steel that means heating it bright red and quenching in canola oil, quenching oil, or canola oil floating on top of room temperature water. Once hardened, the spring must be tempered or it will break. I use a heat treating oven which I can program such that the hardened spring is heated to 750 degrees F for about 1 hour and then left to cool in the shut off oven. That always produces a good spring. You can use a lead bath at about 700 degrees to do much the same or place the spring in a dish coated with motor oil and flaming it until all the oil burns away. Those methods can work but neither are as reliable as a good programmable oven.
dave