Annealing is the process of super-heating and then slowly cooling steel to soften it up and make it workable for your projects. Steel can be annealed in a forge, such as in a blacksmith's shop, in a ceramic kiln or in a furnace. Annealing changes the molecular structure of the steel in order to make it workable; as the steel cools, the molecules realign themselves, resulting in a hardened product.
Annealing in a Box
Place the steel in the cast iron box, packed with insulating material. If the steel is small enough, build a firebrick box in a forge and place the steel inside of the box.
Place the box into the furnace or kiln and heat the steel and box to between 1400 and 1650 degrees, depending on whether you are dealing with high- or low- carbon steel. High-carbon steel can be annealed at lower temperatures than low-carbon steel. The steel should be heated long enough to ensure that it heats throughout.
Turn off the heat source after the steel is heated through, and allow the steel to cool slowly inside of the box; overnight is recommended.