Cold and Hot Working:

Plastic deformation that is carried out in a temperature region and over a time interval like which the strain hardening is not relieved is known as cold work.  Substantial knowledge on the structure of the cold-worked state has been gained. In the previous stages of plastic deformation and slip are essentially on primary glide planes and the dislocations form coplanar arrays. As deformation proceeds, cross slip takes place. A cold-worked structure forms high dislocation density regions which soon established into networks. A grain size decreases along with strain at low deformation but soon reaches a fixed size. Cold working will reduces ductility.

Hot working refers to the procedure where metals are deformed above their recrystallization temperature and strain hardening does not happen. Hot working is commonly performed at elevated temperatures. Lead, therefore, is hot-worked at room temperature since of its low melting temperature. At the other extreme, molybdenum is cold-worked while deformed even at red heat since of its high recrystallization temperature.

The resistance of metals to plastic deformation commonly falls along with temperature. For this purpose, larger massive sections are always worked hot through forging, rolling, or extrusion. A Metals show distinctly viscous features at suitably high temperatures, and their resistance to flow raise at high forming rates. That occurs not only since it is a feature of viscous substances, but since the rate of recrystallization might not be fast sufficient.