Annealing (metallurgy)

Annealing (metallurgy)

Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as hardness and ductility. It is a process that produces conditions by heating to above the critical temperature, maintaining a suitable temperature, and then cooling. Annealing is used to induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous and improve cold working properties. In the cases of copper, steel, silver, and brass, this process is performed by substantially heating the material (generally until glowing) for a while and allowing it to cool. Unlike ferrous metals—which must be cooled slowly to anneal—copper, silver and brass can be cooled slowly in air or quickly by quenching in water. In this fashion the metal is softened and prepared for further work such as shaping, stamping, or forming.

Typically, large ovens are used for the annealing process. The inside of the oven is large enough to place the workpiece in a position to receive maximum exposure to the circulating heated air. For high volume process annealing, gas fired conveyor furnaces are often used. For large workpieces or high quantity parts Car-bottom furnaces will be used in order to move the parts in and out with ease. Once the annealing process has been successfully completed, the workpieces are sometimes left in the oven in order for the parts to have a controlled cooling process. While some workpieces are left in the oven to cool in a controlled fashion, other materials and alloys are removed from the oven. After being removed from the oven, the workpieces are often quickly cooled off in a process known as quench hardening. Some typical methods of quench hardening materials involve the use of media such as air, water, oil, or salt.[citation needed] Quench hardening is generally applicable to some ferrous alloys, but not copper alloys.