Heat Treatment of Metals
When metals are annealed they become softer and can be more easily bent or hammered into a new shape.
Ferrous metals (irons and steels) are heated to cherry red (about 720 degrees) and then allowed to cool slowly.
Copper is heated to dull red (approx.500 degrees) and then allowed to cool slowly as well.
Aluminium only needs to be heated to about 350 - 400 degrees and left to cool. Soap is used to cover the surface before heating when it turns black the correct temperature has been reached.
Hardening and Tempering Steels
When steel is heated to cherry red and the quenched in water it becomes brittle as well as hard. (mild steel is only slightly affected by this process). Tempering takes some of the hardness away but makes the steel tougher. Tempering means reheating to temperatures between 230 and 300 degrees depending on the properties needed and then quenching in oil (water can be used).