Annealing is basically process of a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness in metallurgy and materials science. The process produces conditions by heating and maintaining a suitable temperature, and then cooling. Annealing is used to induce ductility, relieve internal stresses, refine the structure and improve cold working properties.
The purpose of annealing may involve one or more of the following aims:
- To soften the steel and to improve machinability.
- To relieve internal stresses induced by some previous treatment (rolling, forging, uneven cooling).
- To remove coarseness of grain.
In the cases of copper, steel, and brass this process is performed by substantially heating the material (generally until glowing) for a while and allowing it to cool slowly. In this fashion the metal is softened and prepared for further work such as shaping, stamping, or forming.
Annealing process involves the heating and controlled cooling of strip, usually in the coil condition.Almost all cold rolled steel strip will have undergone the annealing process, normally prior to a final "skin pass", a final light reduction.
The stocks of cold rolled steel strip is hot rolled steel strip. Due to process of cold rolled is hot rolled transform after cool off continuously, mechanical properties of spring use the produce is not good and rigidity is very high. This steel stripe usually use to produce products, which don't need stretch or fold. So the steel strip must undergone annealing process, then mechanical properties of spring use resume.
References:
http://springsteelstrip.co.uk/2008/11/11/annealing-steel-strip/