what is hot and cold working of metals?

Cold rolling is a metallurgical process in which metal is passed through a pair of rollers at a temperature below its recrystallization temperature. This process hardens the metal, by compressing and stretching the metal crystals. During the rolling process, the metal is annealed by heating it above the recrystallization temperature after every few rollings, to prevent it from becoming brittle and cracking.[citation needed]

Hot rolling is a metallurgical process in which the metal is passed or deformed between a set of work rolls and the temperature of the metal is generally above its recrystallization temperature, as opposed to cold rolling, which takes place below this temperature. This permits large deformations of the metal to be achieved with a low number of rolling cycles.

Because the metal is worked before crystal structures have formed, this process does not itself affect its microstructural properties. Hot rolling is primarily concerned with manipulating material shape and geometry rather than mechanical properties. This is achieved by heating a component or material to its upper critical temperature and then applying controlled load which forms the material to a desired specification or size.

Mechanical properties of the material in its final as-rolled form is a function of: the material chemistry, reheat temperature, rate of temperature decrease during deformation, rate of deformation, heat of deformation, total reduction, recovery time, recrystallisation time, and subsequent rate of cooling after deformation.

Hot rolling is mainly used to produce sheet metal, or simple cross sections from billets.

Hot rolling is also used to create intermediate products such as slabs.

Working metal hot is heating metal as in forge (blacksmithing) . Cold woking is working with out heating.